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Provides an in-depth analysis of one or a few specific LRD sources (e.g., spectral decomposition of a single object). Presents a list or table of LRD sources, candidates, or related objects with measured/derived properties from a survey. Uses computational models (hydrodynamical, cosmological, radiative transfer) to predict or interpret LRD properties. Primarily discusses theoretical models, physical mechanisms (e.g., seeding mechanisms, accretion modes), or interpretations of LRD phenomena. Summarizes the current state of LRD research, comparing results across multiple surveys and methodologies. Argues that the primary power source and spectral features are driven by an Active Galactic Nucleus (Type 1 or obscured). Discusses or proposes scenarios where AGN activity is sub-dominant or absent (e.g., pure stellar models). Investigates intense, compact star formation activity as a primary or contributing factor to LRD properties. Proposes a hybrid model where both AGN activity and star formation contribute significantly to the observed properties. Specifically investigates super-Eddington accretion regimes to explain the high luminosity and lack of X-rays. Links LRDs to "Heavy Seed" black holes, Direct Collapse Black Holes (DCBH), or over-massive black holes relative to host galaxies. Explores non-standard explanations such as Supermassive Stars, Quasi-stars, Dark Stars, or Dark Matter interactions. Attributes the red color primarily to dust extinction (e.g., dusty torus or host galaxy dust) rather than intrinsic emission color. Studies time-domain changes in brightness or spectral features (or lack thereof) to distinguish between AGN and stellar origins. Discusses observations in the X-ray spectrum (e.g., Chandra), focusing on detections or stacking upper limits. Discusses observations in the radio spectrum (e.g., VLA, LOFAR) to constrain jet activity or star formation rates. Utilizes sub-millimeter/millimeter observations (e.g., ALMA) to constrain dust mass, temperature, and gas content. Focuses on the Spectral Energy Distribution (e.g., the characteristic 'V-shape', UV-turnover, or Balmer break modeling). Analyzes spectra to identify lines (H-alpha, H-beta), measure line widths (FWHM), or detect outflows. Derives properties from imaging/colors (e.g., selecting 'V-shaped' candidates via filter cuts). Utilizes observational data primarily from JWST (NIRCam, NIRSpec, MIRI). Utilizes data from HST, Spitzer, or ground-based telescopes, often for pre-selection or archival comparison. Combines data from significantly different spectral regions (e.g., Optical/IR + X-ray/Radio/ALMA) for a panchromatic view. Pertains to cosmic epochs at high redshift (z > 4), the peak era of the LRD population. Discusses potential analogs to high-z LRDs found in the local or lower-redshift universe (z < 1), such as Green Peas or Blueberries. Discusses estimation of the central SMBH mass, often using virial scaling relations or exploring the M_BH-M_star relation. Focuses on the number density, luminosity function, or cosmic evolution of the LRD population. Analyzes the spatial distribution/environment of LRDs (e.g., halo mass, satellite fraction) to infer their cosmological context. Analyzes spectral emission lines (e.g., Broad vs Narrow Balmer lines, [OIII], [NII]), ratios, or BPT diagnostics. Specifically investigates absorption lines (e.g., Balmer absorption) indicative of dense gas reservoirs or specific stellar populations. Studies properties of the host galaxy (stellar mass, size, morphology) after decomposing the central point source. Examines gas/star motion, velocity dispersion, or outflows derived from line profiles. Focuses on the compactness (unresolved vs resolved), size (effective radius), or structural decomposition of the source. Investigates column densities (N_H), dust attenuation (Av), or gas density responsible for the spectral shape. Describes or critiques the specific color cuts, magnitude limits, or biases used to define the LRD sample.

2026

Origins of the UV Continuum and Balmer Emission Lines in Little Red Dots: Observational Validation of Dense Gas Envelope Models Enshrouding the Active Galactic Nucleus

Yoshihisa Asada, Kohei Inayoshi, Qinyue Fei, and 2 more authors

The Astrophysical Journal Letters, Jul 2026

Abs DOI ADS

We present a statistical study on the origins of the UV continuum and narrow/broad emission lines in little red dots (LRDs), presumably involving active galactic nuclei (AGNs). Leveraging all archived JWST/NIRSpec data, we build a sample of 27 spectroscopically confirmed LRDs at 5 < z_spec < 7.2 by requiring broad H\ensuremathα emission, blue UV colors, V-shaped continua, and compact morphologies. We define a control sample of seven blue, compact, broad-line AGNs without red optical continua (hereafter little blue dots, LBDs) and examine correlations between rest UV and the narrow/broad H\ensuremathα luminosities in these populations. In LRDs, both narrow and broad H\ensuremathα components are tightly correlated with the UV continuum, and the luminosity ratios are consistent with those in young starburst galaxies. In contrast, the UV-to-broad-H\ensuremathα ratios in LBDs closely match local unobscured AGNs and are statistically different from LRDs. The Ly\ensuremathα occurrence rates and strengths do not differ between LRDs and LBDs and are comparable to normal star-forming galaxies. These results are consistent with a scenario where the central black hole in LRDs is enshrouded by a dense opaque gas envelope—in this model, the UV continuum as well as narrow and even broad H\ensuremathα emissions are powered not by AGNs but predominantly by young massive stars surrounding the envelope, while the envelope radiates as a \ensuremath∼5000 K blackbody. As the envelope dissipates, direct AGN emission can emerge, potentially transforming LRDs into LBDs and marking the end of a short-lived phase of rapid black hole growth.

@article{2026ApJ..1005L..22A, author = {{Asada}, Yoshihisa and {Inayoshi}, Kohei and {Fei}, Qinyue and {Fujimoto}, Seiji and {Willott}, Chris J.}, title = {{Origins of the UV Continuum and Balmer Emission Lines in Little Red Dots: Observational Validation of Dense Gas Envelope Models Enshrouding the Active Galactic Nucleus}}, journal = {\apjl}, keywords = {Active galactic nuclei, High-redshift galaxies, Supermassive black holes, AGN host galaxies, 16, 734, 1663, 2017}, year = {2026}, month = jul, volume = {1005}, number = {1}, eid = {L22}, pages = {L22}, doi = {10.3847/2041-8213/ae7d0a}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1005L..22A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, non-agn, obscuration, starburst}, month_numeric = {7} }

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Compact, AGN-hosting Dwarf Galaxies with “Little Red Dot”-like SEDs in the Local Universe

Lulu Bao, Chao-Wei Tsai, Jingwen Wu, and 1 more author

The Astrophysical Journal, Jul 2026

Abs DOI ADS arXiv

Local active galactic nuclei (AGNs) in dwarf galaxies are often considered as analogs for the earliest supermassive black holes, although their connections require more comprehensive examinations. Motivated by finding the local analogs of “Little Red Dots” (LRDs), the compact, red galaxies discovered by JWST and at z > 5, characterized by “V-shaped” spectral energy distributions (SEDs), we compile a sample of local AGN-hosting dwarf galaxies (ADGs) with comparable luminosities to statistically evaluate this connection. By applying K-means clustering to SED shapes and morphological sizes, we classified four groups that trace a sequence in physical properties, including metallicity, star formation rate, and dust emission, mainly driven by their distinct UV─optical slopes. Within these groups, we find that about half of the ADGs exhibit “V-shaped” SEDs and relatively compact morphologies. However, a direct comparison reveals fundamental physical differences: local “V-shaped,” compact ADGs appear significantly more evolved than high-z LRDs, characterized by systematically larger effective radii and distinct ionization states. Our results suggest that local compact ADGs likely follow a different formation pathway from LRDs, highlighting the complexity of black hole─galaxy coevolution across cosmic time.

@article{2026ApJ..1005..143B, author = {{Bao}, Lulu and {Tsai}, Chao-Wei and {Wu}, Jingwen and {Wang}, Jialai}, title = {{Compact, AGN-hosting Dwarf Galaxies with ``Little Red Dot''-like SEDs in the Local Universe}}, journal = {\apj}, keywords = {Dwarf galaxies, Active galactic nuclei, Galaxy evolution, 416, 16, 594}, year = {2026}, month = jul, volume = {1005}, number = {2}, eid = {143}, pages = {143}, doi = {10.3847/1538-4357/ae6fa8}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1005..143B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, local counterpart, morphology, sed}, eprint = {2605.04685}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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The gravitational-wave fingerprint of dynamically assembled primordial black hole cluster seeds in JWST’s Little Red Dots

Juan Garcia-Bellido

arXiv e-prints, Jul 2026

Abs ADS arXiv

The James Webb Space Telescope (JWST) has revealed compact, red, overmassive accreting black holes - the so-called “Little Red Dots” (LRDs) - in chemically near-pristine hosts at z\simeq5 - 9, straining standard heavy-seed models. We show that a population of strongly clustered primordial black holes (PBH) with a broad mass function predicted by a QCD-epoch thermal history naturally realizes the configuration that assembles LRD- scale seeds: an intermediate-mass PBH \textbackslashemph{nucleus} M_\rm BH\sim10^3-10^5 M_⊙surrounded, within a few parsecs, by a swarm of light (m\sim30 M_⊙) PBHs embedded in dense baryonic gas. Gas dynamical friction keeps the loss cone full and lets the core contract, so the swarm sinks and is swallowed on t_\rm seed\sim10-50 Myr, well inside the cosmic time at z\sim10-15. Because a heavy nucleus is present \textbackslashemph{ab initio}, the captures occur at extreme mass ratio q\sim10^-4-10^-2: the remnant is retained against gravitational recoil, and each capture reaches the innermost stable orbit under gravitational-wave (GW) emission, radiating \simeq0.06 m c^2 so that the assembly efficiency is ζ\simeq0.06 independent of M_\rm BH. The superposed swarm inspirals form a stochastic background Ω_\rm GW h^2\sim10^-13-10^-11 with a Ω_\rm GW∝f^2/3 shape truncated below the gas-decoupling frequency and topped by a ringdown “comb” at f_\rm ring(M_\rm BH)\simeq13 mHz for 10^5 M_⊙and \simeq1.3 Hz for 10^3 M_⊙nuclei at z_f\simeq12. The few comparable-mass nucleus-nucleus coalescences are instead individually resolvable LISA/deci-Hz sources. Detection, and discrimination of these signatures from a directly formed PBH seed of the same mass, would identify the LRDs as PBH-nucleus seeded black holes.

@article{2026arXiv260709201G, author = {{Garcia-Bellido}, Juan}, title = {{The gravitational-wave fingerprint of dynamically assembled primordial black hole cluster seeds in JWST's Little Red Dots}}, journal = {arXiv e-prints}, keywords = {General Relativity and Quantum Cosmology}, year = {2026}, month = jul, eid = {arXiv:2607.09201}, pages = {arXiv:2607.09201}, archiveprefix = {arXiv}, eprint = {2607.09201}, primaryclass = {gr-qc}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260709201G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, exotic physics, heavy seed, theory}, month_numeric = {7} }

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Spatial decomposition of Little Red Dots with JWST/NIRSpec IFU into broad-line red cores and narrow-line blue host galaxies

Yuzo Ishikawa, Anna-Christina Eilers, Rohan P. Naidu, and 11 more authors

arXiv e-prints, Jul 2026

Abs ADS arXiv

Little Red Dots (LRDs) are a population of compact red sources discovered by the James Webb Space Telescope (JWST). Imaging and spectroscopy have shown that LRDs exhibit a complex spectrum with a “V-shaped” continuum, broad Balmer emission lines, and in some cases Balmer absorption. While the physical origin of these components remains debated, recent studies propose that they arise from a compact central engine likely hosting a rapidly growing black hole embedded within a more extended host galaxy. We test this central engine + host galaxy model using JWST/NIRSpec integral field unit (IFU) spectroscopy to spectrally decompose the observed continuum, narrow and broad emission lines, and absorption. We spatially map each component for five broad Ha-selected LRDs at z\raisebox-0.5ex\textasciitilde5 observed with both the prism and high-resolution G395H grating. We find that the blue continuum emission is co-spatial with the narrow emission line region, while the red continuum arises from a compact core co- spatial with the broad Balmer emission and absorption. Spatial maps of the [OIII] equivalent width reveal a pronounced decrease in the central core. Our work provides further evidence that the LRD emission is produced by at least two distinct physical components arising from a red central engine embedded within a blue host galaxy.

@article{2026arXiv260709647I, author = {{Ishikawa}, Yuzo and {Eilers}, Anna-Christina and {Naidu}, Rohan P. and {Matthee}, Jorryt and {Bordoloi}, Rongmon and {Chisholm}, John and {Greene}, Jenny E. and {Ma}, Yilun and {Oesch}, Pascal A. and {Sun}, Wendy Q. and {Torralba}, Alberto and {Weaver}, John R. and {Wuyts}, Stijn and {Xiao}, Mengyuan}, title = {{Spatial decomposition of Little Red Dots with JWST/NIRSpec IFU into broad-line red cores and narrow-line blue host galaxies}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jul, eid = {arXiv:2607.09647}, pages = {arXiv:2607.09647}, archiveprefix = {arXiv}, eprint = {2607.09647}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260709647I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, emission lines, host galaxy, jwst, spectroscopy}, month_numeric = {7} }

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Tracing the Evolution of the Balmer Break from Cosmic Dawn to Cosmic Noon with JWST

Adarsh Kuruvanthodi, Daniel Schaerer, Rui Marques-Chaves, and 3 more authors

arXiv e-prints, Jul 2026

Abs DOI ADS arXiv

The Balmer break (BB) is a key spectral feature for constraining stellar population ages, star formation histories, and redshifts of high-redshift sources. The redshift evolution and distribution of BB strength, together with the properties of BB galaxies, constrain stellar population characteristics and the nature of star formation across cosmic epochs. However, a systematic and unbiased characterization of BB strengths across the full galaxy population remains limited with the James Webb Space Telescope (JWST). We aim to characterize the redshift evolution of BB strength over z=3.5-10 and its distribution across different epochs using photometry. We also examine correlations between BB strength and key physical parameters within these redshift intervals. We further assess the implications of BB galaxies for the nature of star formation and stellar populations at z>3.5. We used the JWST NIRCam photometric observations taken as part of various programs, including CEERS, JADES, FRESCO, and PRIMER. We estimated the BB strength of the objects with two adjacent broadband filters in various redshift windows between redshifts 3 and 10, which exclude strong line contamination. We employ the SED-fitting code CIGALE for both SED fitting and the generation of mock galaxy simulations. We find that the median Balmer break strength (expressed as a flux ratio) increases from cosmic dawn to cosmic noon, from 1.1 to 1.5, primarily driven by the age of the stellar population. These estimations are in agreement with the latest spectroscopic estimations in the literature. We identify objects with extremely large BB strengths (BB>3.0) at z=3.5-4 and z=7-10, indicating strong extinction combined with an old stellar population and the presence of Little Red Dots (LRDs) in the former, and predominantly LRDs in the latter.[abridged]

@article{2026arXiv260707698K, author = {{Kuruvanthodi}, Adarsh and {Schaerer}, Daniel and {Marques-Chaves}, Rui and {Weibel}, Andrea and {Korber}, Damien and {Charbonnel}, Corinne}, title = {{Tracing the Evolution of the Balmer Break from Cosmic Dawn to Cosmic Noon with JWST}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jul, eid = {arXiv:2607.07698}, pages = {arXiv:2607.07698}, doi = {10.48550/arXiv.2607.07698}, archiveprefix = {arXiv}, eprint = {2607.07698}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260707698K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, jwst, photometry, sed}, month_numeric = {7} }

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The MIRI Early Obscured-AGN Wide Survey (MEOW): A Population of Hidden AGN at z rsim 5 Revealed by JWST/MIRI Imaging

Gene C. K. Leung, Anna-Christina Eilers, Ryan Endsley, and 25 more authors

arXiv e-prints, Jul 2026

Abs ADS arXiv

We present the MIRI Early Obscured-AGN Wide Survey (MEOW), a JWST/MIRI imaging survey designed to detect dust-obscured active galactic nuclei (AGN) across cosmic time, with a particular focus on the high-redshift universe at z rsim 5. MEOW observes the GOODS-N and GOODS-S fields with 43 pointings covering 95 arcmin^2 with the F1000W and F2100W filters, reaching depths of 0.5 and 3.6 μJy (5σ), respectively. Using spectral energy distribution (SED) modeling combining MEOW photometry with archival HST, JWST/NIRCam, and SCUBA-2 data, we identify a sample of 16 MIRI- selected AGN at z = 4.5–7.2 (12 spectroscopically confirmed), spanning bolometric luminosities of L_\rm bol = 1 0^44.6–10^46.4\raisebox-0.5ex\textasciitildeerg\raiseb ox-0.5ex\textasciitildes^-1. Twelve of the 16 AGN are newly identified in this work, including at least five narrow- line AGN representing the obscured population to which broad- line spectroscopic searches are insensitive. Two broad-line AGN exhibit markedly different mid-infrared emission properties, consistent with one being a little red dot (LRD) and the other either a typical AGN or an LRD with unusually strong hot-dust emission. The MIRI-selected AGN bolometric luminosity function at z = 4.5–6 yields number densities comparable to those of broad-line AGN and LRDs, suggesting that obscured AGN contribute significantly to the total AGN census at these epochs. The narrow-line AGN reside in diverse host environments, with evidence for both circumnuclear and host-galaxy-scale obscuration, pointing to multiple physical mechanisms at work. These results establish JWST/MIRI imaging as an indispensable component of a multi-faceted approach to a complete census of early supermassive black hole growth.

@article{2026arXiv260702666L, author = {{Leung}, Gene C. K. and {Eilers}, Anna-Christina and {Endsley}, Ryan and {Finkelstein}, Steven L. and {Bagley}, Micaela B. and {Barro}, Guillermo and {Koekemoer}, Anton M. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Pirzkal}, Nor and {Backhaus}, Bren E. and {Bulichi}, Teodora-Elena and {Champagne}, Jaclyn B. and {Chworowsky}, Katherine and {Cleri}, Nikko J. and {Dickinson}, Mark and {Fan}, Xiaohui and {Fujimoto}, Seiji and {Grogin}, Norman A. and {Kirkpatrick}, Allison and {Kocevski}, Dale D. and {Kokorev}, Vasily and {Larson}, Rebecca L. and {Lucas}, Ray A. and {Pacucci}, Fabio and {Papovich}, Casey and {Taylor}, Anthony J. and {Villanueva}, Natalia C. and {Yang}, Guang}, title = {{The MIRI Early Obscured-AGN Wide Survey (MEOW): A Population of Hidden AGN at $z rsim 5$ Revealed by JWST/MIRI Imaging}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jul, eid = {arXiv:2607.02666}, pages = {arXiv:2607.02666}, archiveprefix = {arXiv}, eprint = {2607.02666}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260702666L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, early universe, jwst, obscuration, sed}, month_numeric = {7} }

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Little Red Dot Progenitors from Compact Starbursts: A Natural Path to Early AGN Formation

Matı́as Liempi, Muhammad A. Latif, and Dominik R. G. Schleicher

The Astrophysical Journal, Jul 2026

Abs DOI ADS arXiv

The recent discovery of little red dots (LRDs) by the James Webb Space Telescope has challenged traditional models of early galaxy and black hole coevolution. The nature of these highly compact objects remains heavily debated, with explanations divided between dust-reddened active galactic nuclei (AGN) and extremely dense stellar populations. We perform high-resolution cosmological simulations to model the formation of LRD precursors. Motivated by recent high-redshift observations and theoretical results, we specifically explore environments characterized by high star formation efficiencies (30% and 100%) and confined feedback. Our simulations naturally produce highly compact galaxies with stellar masses of 10^7─6 \texttimes 10^8 M_\ensuremath⊙, with most of the mass concentrated within 200─300 pc. We find that, in these dense environments, gas inflows, gravitational torques, and stellar dynamical friction operate on highly efficient timescales. Over a 10 Myr timescale, gas inflows can accumulate \ensuremath∼10^7 M_\ensuremath⊙ at the galactic center, while gravitational torques and dynamical friction can contribute an additional 10^5─10^9 M_\ensuremath⊙ and 10^3─10^4 M_\ensuremath⊙ through the inward migration of massive stars. Assuming a conservative 10% efficiency to account for feedback, this rapid mass accumulation can lead to the formation of a \ensuremath∼10^6 M_\ensuremath⊙ central black hole, naturally giving rise to an AGN in these dense systems. Therefore, stellar and AGN interpretations of LRDs may not be mutually exclusive; rather, dense stellar systems are likely precursors to AGN.

@article{2026ApJ..1005..174L, author = {{Liempi}, Mat{\'\i}as and {Latif}, Muhammad A. and {Schleicher}, Dominik R. G.}, title = {{Little Red Dot Progenitors from Compact Starbursts: A Natural Path to Early AGN Formation}}, journal = {\apj}, keywords = {Supermassive black holes, High-redshift galaxies, Astronomical simulations, 1663, 734, 1857}, year = {2026}, month = jul, volume = {1005}, number = {2}, eid = {174}, pages = {174}, doi = {10.3847/1538-4357/ae7710}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1005..174L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, early universe, simulation, starburst, theory}, eprint = {2606.03375}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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Local Analogs of Little Red Dots: Optical Variability and Evidence for an Active Galactic Nucleus Origin

Ruqiu Lin, Zhen-Ya Zheng, Junxian Wang, and 9 more authors

The Astrophysical Journal, Jul 2026

Abs DOI ADS arXiv

Little red dots (LRDs) draw extensive attention because of their unique observational characteristics and apparent overabundance in the early Universe, raising new insights into early black hole formation and growth. Early studies show that LRDs exhibit weak variability in photometry and emission-line fluxes, suggesting a preference for super-Eddington accretion or disfavoring an active galactic nucleus (AGN) origin. However, the current data are limited, preventing us from placing strong constraints on their variability. Based on Zwicky Transient Facility (ZTF) light curves with a baseline of \ensuremath∼6 yr, we here study the optical variability of seven previously reported local analogs of LRDs at z \ensuremath∼ 0.3, offering an insight into LRDs from a low-redshift sample. Three out of seven local analogs show excess variances on all three bands of their light curves, and two of them can be fitted with the damping random walk model, supporting their AGN origins for the variability. The remaining sources show weak variance in at least one band, but no detectable variability, exhibiting SF_\ensuremath∞ upper limits consistent with estimates from high-redshift LRDs. Their nondetection of variability is likely due to the large photometric uncertainty. As an implication, by simulating long baseline light curves with the variability amplitude of local analogs and adopting JWST observation cadence, we investigate the limitation of the variability amplitude estimate for LRDs. Our mock observations imply that the current constraints on LRDs’ variability are probably underestimated. This underestimation might be induced by the short temporal baseline of observations, as well as the intrinsic scatter of the empirical M_BH─\ensuremathτ relation.

@article{2026ApJ..1005..150L, author = {{Lin}, Ruqiu and {Zheng}, Zhen-Ya and {Wang}, Junxian and {Ho}, Luis C. and {Zavala}, Jorge A. and {Zhang}, Zijian and {Jiang}, Chunyan and {Lin}, Jiaqi and {Yuan}, Fang-Ting and {Jiang}, Linhua and {Wang}, Tinggui and {Zhang}, Xiaer}, title = {{Local Analogs of Little Red Dots: Optical Variability and Evidence for an Active Galactic Nucleus Origin}}, journal = {\apj}, keywords = {Active galaxies, Compact dwarf galaxies, Supermassive black holes, Active galactic nuclei, 17, 281, 1663, 16}, year = {2026}, month = jul, volume = {1005}, number = {2}, eid = {150}, pages = {150}, doi = {10.3847/1538-4357/ae74c6}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1005..150L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, local counterpart, non-jwst, simulation, variability}, eprint = {2603.01473}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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Mephisto: Self-improving Large Language Model─based Agents for Automated Interpretation of Multiband Galaxy Observations

Zechang Sun, Yuan-Sen Ting, Yaobo Liang, and 3 more authors

The Astrophysical Journal Supplement Series, Jul 2026

Abs DOI ADS arXiv

Astronomical research has long relied on human expertise to interpret complex data and formulate scientific hypotheses. In this study, we introduce Mephisto—a multiagent collaboration framework powered by large language models (LLMs) that emulates human-like reasoning to analyze multiband galaxy observations. Mephisto interfaces with the CIGALE codebase (a library of spectral energy distribution models) to iteratively refine physical models against observational data. It conducts deliberate reasoning via a tree search, accumulates knowledge through self-play, dynamically updates its knowledge base, and is validated across diverse galaxy populations—including the James Webb Space Telescope’s recently discovered “little red dot” galaxies. We show that Mephisto demonstrates the ability to infer the physical properties of galaxies from multiband photometry, positioning it as a research copilot for astronomers. Unlike prior black-box machine learning approaches in astronomy, Mephisto offers a transparent, human-aligned reasoning process that integrates with existing research practices. This work underscores the possibility of LLM-driven agent-based research for astronomy, establishes a foundation for fully automated, end-to-end artificial intelligence (AI)-powered scientific workflows, and opens up new avenues for AI-augmented discoveries in astronomy.

@article{2026ApJS..285...28S, author = {{Sun}, Zechang and {Ting}, Yuan-Sen and {Liang}, Yaobo and {Duan}, Nan and {Huang}, Song and {Cai}, Zheng}, title = {{Mephisto: Self-improving Large Language Model─based Agents for Automated Interpretation of Multiband Galaxy Observations}}, journal = {\apjs}, keywords = {Astronomical research, Astronomy data analysis, Galaxy physics, Spectral energy distribution, 91, 1858, 612, 2129}, year = {2026}, month = jul, volume = {285}, number = {1}, eid = {28}, pages = {28}, doi = {10.3847/1538-4365/ae5d3a}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJS..285...28S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, photometry, sed}, eprint = {2510.08354}, archiveprefix = {arXiv}, primaryclass = {astro-ph.IM}, month_numeric = {7} }

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A Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7

Alberto Torralba, Jorryt Matthee, Andrea Weibel, and 12 more authors

The Astrophysical Journal Letters, Jul 2026

Abs DOI ADS arXiv

Recent studies at high redshift have revealed an enigmatic class of little red dots (LRDs) with extreme Balmer breaks, stronger than in any stellar atmosphere. However, it is unclear whether such objects exist at lower redshift, especially given the low number of LRDs reported at z \ensuremath≲ 2. Here, we report the discovery of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.73, identified from JWST/NIRCam pure-parallel imaging taken by the PANORAMIC survey, and confirmed by deep VLT/X-Shooter spectroscopy. The rest-optical to near-infrared spectral energy distribution of PAN-BH*-1 is consistent with a photospheric continuum with effective temperature T_eff ≍ 4800 K. The broad H\ensuremathα emission line shows remarkably deep absorption, stronger than previously measured in any LRD. The absorption trough spans from \ensuremath-520 to +267 km s^\ensuremath-1 with respect to the systemic redshift. The presence of blue- and red-shifted absorption suggests complex dynamics of the obscuring gas along the line of sight. We speculate that the absorption trough can be produced by a thick wind launched from a thick, rotating photospheric disk, the latter being the source of the red optical continuum. While the source is unresolved in the rest-optical JWST data (r_eff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with reff=1.0\ensuremath-0.3+0.5 kpc, which we interpret as a host galaxy with a stellar mass of \ensuremath∼10^8 M_\ensuremath⊙, in line with the narrow H\ensuremathα emission. The discovery of this object at cosmic noon highlights the feasibility of systematic searches for extreme LRDs with wide-area facilities such as Euclid and Roman.

@article{2026ApJ..1005L..37T, author = {{Torralba}, Alberto and {Matthee}, Jorryt and {Weibel}, Andrea and {Naidu}, Rohan P. and {Ma}, Yilun and {Cloonan}, Aidan P. and {Desai}, Aayush and {de Graaff}, Anna and {Greene}, Jenny E. and {Jespersen}, Christian Kragh and {Kramarenko}, Ivan G. and {Mascia}, Sara and {Oesch}, Pascal A. and {Sun}, Wendy Q. and {Williams}, Christina C.}, title = {{A Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7}}, journal = {\apjl}, keywords = {Black holes, Active galactic nuclei, High-redshift galaxies, 162, 16, 734}, year = {2026}, month = jul, volume = {1005}, number = {2}, eid = {L37}, pages = {L37}, doi = {10.3847/2041-8213/ae7bfd}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1005L..37T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, case study, jwst, sed, spectroscopy}, eprint = {2603.28335}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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High-redshift Galaxy Candidates at z = 6+ as Revealed by JWST Observations of MACS0647

Keduse Worku, Tiger Yu-Yang Hsiao, Dan Coe, and 9 more authors

The Astrophysical Journal, Jul 2026

Abs DOI ADS

We present a catalog of 57 high-redshift z > 6 galaxy candidates, including 14 spectroscopic confirmations (z = 6.10─9.25), 2 little red dots (z = 4.77, 5.81), and 2 interlopers (z = 3.23, 3.72), based on JWST NIRCam imaging (seven filters), NIRSpec spectroscopy (PRISM and G395H), and archival HST imaging (17 filters) of the strong lensing galaxy cluster MACS0647. Our highest redshift confirmation (z = 9.25) is an extremely blue galaxy, and here we identify a spectral turnover likely due to damped Ly\ensuremathα. We identify an overdensity of galaxies with spectroscopic redshifts z = 6.1, confirming the z \ensuremath∼ 6 overdensity identified in HST images. In one of these galaxies, our high-resolution G395H spectroscopy reveals two spatially resolved components with a velocity difference of \ensuremath∼90 km s^\ensuremath-1; if these components are gravitationally bound, this would imply a dynamical mass on the order of \ensuremath∼10^8M_\ensuremath⊙ given their projected separation. We present spectral line fluxes, widths, and derived physical properties, including stellar masses (10^8─10^9 M_\ensuremath⊙) and metallicities (10%─40% Z_\ensuremath⊙) for our spectroscopic sample. We note half of our NIRSpec data was obtained with standard three-slitlet nods and half was obtained with single slitlets yielding similar results, demonstrating the power to observe more sources on a densely packed NIRSpec microshutter assembly.

@article{2026ApJ..1005...11W, author = {{Worku}, Keduse and {Hsiao}, Tiger Yu-Yang and {Coe}, Dan and {Abdurro'uf} and {Resseguier}, Tom and {Larson}, Rebecca L. and {Antwi-Danso}, Jacqueline and {Brammer}, Gabriel and {Kokorev}, Vasily and {Bradley}, Larry D. and {Furtak}, Lukas J. and {Oguri}, Masamune}, title = {{High-redshift Galaxy Candidates at z = 6+ as Revealed by JWST Observations of MACS0647}}, journal = {\apj}, keywords = {High-redshift galaxies, Catalogs, Spectroscopy, Photometry, 734, 205, 1558, 1234}, year = {2026}, month = jul, volume = {1005}, number = {1}, eid = {11}, pages = {11}, doi = {10.3847/1538-4357/ae6cdf}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1005...11W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {catalog, early universe, emission lines, jwst, spectroscopy}, month_numeric = {7} }

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Memoirs of the curvaton: non-perturbative non-Gaussianity and supermassive primordial black holes

S. Allegrini, A. J. Iovino, G. Perna, and 1 more author

arXiv e-prints, Jun 2026

Abs ADS arXiv

The curvaton provides a simple mechanism for generating strongly non- Gaussian curvature perturbations after inflation, with potentially important consequences on small scales. We study curvaton dynamics beyond the standard quadratic potential and construct the local non-Gaussian map ζ=F(ζ_\rm G) relating the curvature perturbation to an auxiliary Gaussian field ζ_\rm G. Curvaton self-interactions make the onset of oscillations field dependent and modify the effective equation of state once the curvaton enters the adiabatic regime. We incorporate these effects using the abbreviated action, which provides a compact way to connect the frozen and oscillatory regimes and exposes sources of non-Gaussianity absent in the purely quadratic case. We apply the formalism to quadratic, monomial, quartic, and cosine potentials, for which we derive the mapping F(ζ_\rm G) and show that self-interactions can either enhance or suppress the resulting non-Gaussianity depending on the potential and initial conditions. We consider non-perturbative aspects in the strongly non-Gaussian regime, and show how strong non-Gaussianity can suppress the power spectrum. As an application, we provide a bottom-up scenario in which strongly positive curvaton non-Gaussianity allows primordial supermassive black hole seeds at peak amplitudes \mathcalA_\rm pk\sim10^-5, which are compatible with the COBE/FIRAS μ-distortion bounds. This opens a new primordial scenario for the Little Red Dots observed by the JWST. The axion-like curvaton provides a particularly natural setting for this mechanism.

@article{2026arXiv260628296A, author = {{Allegrini}, S. and {Iovino}, A. J. and {Perna}, G. and {Veerm{\"a}e}, H.}, title = {{Memoirs of the curvaton: non-perturbative non-Gaussianity and supermassive primordial black holes}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology}, year = {2026}, month = jun, eid = {arXiv:2606.28296}, pages = {arXiv:2606.28296}, archiveprefix = {arXiv}, eprint = {2606.28296}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260628296A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, heavy seed, theory}, month_numeric = {6} }

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The UV Side of Little Red Dots: Red, Compact, and Iron-Enhanced Rest-UV Emission with a Strong Downturn around Lyα

Makoto Ando, Yuichi Harikane, Harley Katz, and 2 more authors

arXiv e-prints, Jun 2026

Abs DOI ADS arXiv

Little Red Dots (LRDs) are candidates for growing supermassive black holes newly discovered by the James Webb Space Telescope (JWST), characterized by compact rest-optical morphology, V-shaped spectra, and broad Hydrogen Balmer lines. While recently proposed BH-star/envelope models have made progress in explaining their optical features, their rest-UV emission, which is considered to originate from host galaxies, remains poorly investigated. In this paper, we present a comprehensive analysis of the UV emission, including continuum shapes, emission line strengths, and morphology, using \sim100 LRDs selected from the JWST spectral archive. Compared to star-forming galaxies at the same redshifts and UV magnitudes, LRDs show systematically redder UV slopes and more compact UV sizes, indicating that their UV emission cannot be explained solely by normal star- forming galaxies and requires a significant contribution from central red and compact emission. From stacked spectra, we find that the Balmer break strength, UV slope, downturn depth around Lyα, and \mathrmFe\,II equivalent width are positively correlated, while the UV size is anticorrelated with the Balmer break strength, suggesting that diversity in the UV continuum shape reflects the varying dominance of the central emission relative to its host. We also measure \mathrmFe\,II//Mg\,II\sim8-10, higher than in quasars at similar redshifts, further supporting a substantial contribution from the central component. Spectral modeling suggests that the observed red UV continuum cannot be reproduced by host galaxy emission alone, but requires an additional very red continuum source (β_\mathrmUV\sim0), possibly nebular continuum emission leaking from dense ionized gas through a clumpy or porous neutral gas envelope.

@article{2026arXiv260603522A, author = {{Ando}, Makoto and {Harikane}, Yuichi and {Katz}, Harley and {Inayoshi}, Kohei and {Tanaka}, Takumi S.}, title = {{The UV Side of Little Red Dots: Red, Compact, and Iron-Enhanced Rest-UV Emission with a Strong Downturn around Ly$α$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.03522}, pages = {arXiv:2606.03522}, doi = {10.48550/arXiv.2606.03522}, archiveprefix = {arXiv}, eprint = {2606.03522}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260603522A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, jwst, morphology, sed, spectroscopy}, month_numeric = {6} }

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A Redshift-based Red Selection of Dusty Star-forming Galaxies

A. J. Barger, L. L. Cowie, S. J. McKay, and 1 more author

The Astrophysical Journal, Jun 2026

Abs DOI ADS

We use JWST observations (1.5─4.44 \ensuremathμm), together with complete Atacama Large Millimeter/submillimeter Array (ALMA) observations (870 \ensuremathμm and/or 1.2 mm), of the massive lensing cluster field A2744 to show that galaxies between z = 1.5 and z = 5.5 with rest-frame red colors f_J/f_V > 3 correspond to dusty star-forming galaxies (DSFGs), little red dots (LRDs), and quiescent galaxies. The color selection picks out 34 of the 41 >4.5\ensuremathσ ALMA sources in the field (83%). We find that the luminous (rest-frame L_\ensuremathν(1.22 \ensuremathμm) > 3.6 \texttimes 10^29 erg s^\ensuremath-1 Hz^\ensuremath-1) red sources are generally extended, while the less luminous red sources are almost all compact and correspond to the LRD population. We also find that the great majority of the luminous, extended red sources are DSFGs based on the ALMA data, with a small admixture of quiescent galaxies at z \ensuremath≲ 3─4 that we identify based on their location in the rest-frame U \ensuremath- V versus V \ensuremath- J diagram. We do not detect any LRDs or quiescent galaxies at the >3\ensuremathσ level in the ALMA images. Roughly 10% of the DSFGs have high rest-frame X-ray luminosities (here L(8─28 keV) > 2.5 \texttimes 10^43 erg s^\ensuremath-1) and must be dominated by active galactic nuclei. The DSFGs and quiescent galaxies nearly all have M_* > 10^10 M_\ensuremath⊙. These massive galaxies become rare at z > 5, paralleling the falloff in the number of detected DSFGs.

@article{2026ApJ..1004..241B, author = {{Barger}, A. J. and {Cowie}, L. L. and {McKay}, S. J. and {Bauer}, F. E.}, title = {{A Redshift-based Red Selection of Dusty Star-forming Galaxies}}, journal = {\apj}, keywords = {Galaxies, 573}, year = {2026}, month = jun, volume = {1004}, number = {2}, eid = {241}, pages = {241}, doi = {10.3847/1538-4357/ae7101}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1004..241B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {alma, dust-reddened, jwst, multi-wavelength, sample selection}, month_numeric = {6} }

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Too Quiet for Comfort: Local Little Red Dots Lack Variability over Decades

Colin J. Burke, Zachary Stone, Yue Shen, and 1 more author

The Astrophysical Journal, Jun 2026

Abs DOI ADS arXiv

Several local (z \ensuremath≲ 0.2) metal-poor dwarf active galactic nuclei (AGNs) have remarkably similar properties to those of high-redshift little red dots (LRDs), and are proposed to be local analogs of LRDs. We use long-term photometric and spectroscopic observations of three local LRDs spanning \ensuremath∼20 yr to measure variability in their rest- frame optical continua and broad H\ensuremathα emission lines. Using Zwicky Transient Facility light curves over a rest- frame \ensuremath∼5 yr baseline, the r-band intrinsic rms variability is (9\texttimes10\ensuremath-5)\ensuremath- 9\texttimes10-5+0.014 mag (J1022+0841), 0.025 \ensuremath\pm 0.004 mag (J1025+1402) and 0.020 \ensuremath\pm 0.005 mag (J1047+0739), indicating low intrinsic variability (<3%─4% at 3\ensuremathσ). These variability amplitudes are much lower than those for dwarf AGNs and more massive quasars. We constrain the broad H\ensuremathα variability to be less than a few percent, without significant profile changes, over a rest-frame baseline of \ensuremath∼15 yr in J1025+1402 and J1047+0739, respectively. Local LRDs have exceptionally large H\ensuremathα equivalent widths and H\ensuremathα/H\ensuremathβ ratios that far exceed the Case B recombination value, in contrast with normal broad-line AGNs. In the context of recent theoretical models of LRDs as dense gas-enshrouded massive black holes with super- Eddington accretion, our results suggest that the photosphere emission is long-term stable and the broad Balmer lines do not arise primarily by photoionization. This scenario is consistent with the lack of variability, large H\ensuremathα/H\ensuremathβ ratios, little dust extinction, and expected high gas density. Virial black hole mass estimates using broad H\ensuremathα assuming photoionization are therefore highly questionable for LRDs.

@article{2026ApJ..1004...16B, author = {{Burke}, Colin J. and {Stone}, Zachary and {Shen}, Yue and {Jiang}, Yan-Fei}, title = {{Too Quiet for Comfort: Local Little Red Dots Lack Variability over Decades}}, journal = {\apj}, keywords = {Active galactic nuclei, High-redshift galaxies, Supermassive black holes, 16, 734, 1663}, year = {2026}, month = jun, volume = {1004}, number = {1}, eid = {16}, pages = {16}, doi = {10.3847/1538-4357/ae6b89}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1004...16B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2511.16082}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {black hole mass, emission lines, local counterpart, super-eddington, variability}, month_numeric = {6} }

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A Population of Little Red Dot-like Quasars in SDSS

Quinn O. Casey, Ryan C. Hickox, Nikko J. Cleri, and 6 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Compact and red sources in the high redshift (z\sim5) Universe, known as “Little Red Dots” (LRDs), are among JWST’s most intriguing discoveries. These sources have broad Balmer emission lines, weak X-ray emission, and unique spectral energy distributions (SEDs) poorly fit by either stellar or AGN templates. Local analogs of LRDs allow for detailed studies of the underlying physical processes with archival multi-wavelength datasets unavailable in the high-z Universe. We show that the SDSS ugriz filters at z\approx0.4, 0.8 overlap well with the JWST filters used to select LRDs at z\sim5. We use SDSS quasars to define a sample of \sim1300 Local Red Dots (LoRDs) which share the same photometric colors of LRDs. A subset of the LoRD sample selected to have V-shaped continua (N=244) show prominent higher-order Balmer absorption features and [NeV]λ3426 emission, both of which would likely be missed in JWST/PRISM observations given the low spectral resolution. A composite SED of the LoRDs differs from a typical quasar SED in the rest-frame UV/optical, but the two agree with each other in the NIR. The LoRD SED matches well with a stack of LRDs and can be modeled either as a reddened AGN combined with a host galaxy, or as a reddened AGN combined with a host galaxy and a cool blackbody. Interestingly, the LoRDs are X-ray detected at a rate comparable to typical quasars. However, the probability that LoRDs and typical quasars would go undetected, if subject to the LRD X-ray upper limits, is >50%.

@article{2026arXiv260626098C, author = {{Casey}, Quinn O. and {Hickox}, Ryan C. and {Cleri}, Nikko J. and {Cohn}, Jonathan H. and {Alexander}, David M. and {Durodola}, Emmanuel and {Whalen}, Kelly E. and {Hviding}, Raphael E. and {Ananna}, Tonima Tasnim}, title = {{A Population of Little Red Dot-like Quasars in SDSS}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.26098}, pages = {arXiv:2606.26098}, archiveprefix = {arXiv}, eprint = {2606.26098}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260626098C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, dust-reddened, local counterpart, sed, x-ray}, month_numeric = {6} }

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ABCD: The Nuclear Structure of the Little Red Dots Revealted through Absorption, Break, Continuum, and Decrement

Chang-Hao Chen, Jinyi Shangguan, Luis C. Ho, and 3 more authors

arXiv e-prints, Jun 2026

Abs DOI ADS arXiv

We present a spectroscopic analysis of 14 little red dots (LRDs) at redshifts 2.2 < z < 6.7 using NIRSpec/MSA prism and medium- resolution grating observations, aiming to constrain the nuclear gas structure through Balmer emission-line profiles, absorption features, relative line intensities, and continuum properties. We simultaneously decompose the broad, narrow, and absorption components of \rm H α, \rm H β, and \rm H γ, and measure both integrated line ratios and velocity-resolved Balmer decrements. The narrow-line Balmer decrements are broadly consistent with Case\raisebox-0.5ex\textasciitildeB recombination modified by mild dust attenuation, while the broad-line decrements are elevated to levels consistent with photoionization models of high-density gas at n_\rm H rsim 10^9 \rm cm^-3. Velocity-resolved Balmer decrements in five sources with highest signal-to-noise ratio are centrally peaked. Assuming virialized broad-line region dynamics, our model can reproduce the Balmer decrement profiles in three sources using a radial density profile with a power-law index β<2. The Balmer absorption lines detected in six sources yield absorber covering factors exceeding 50%. Sources with blueshifted absorption lines tend to have elevated narrow-line Balmer decrement, suggesting a connection between dust content and the presence of outflow. Comparing the incident luminosity inferred from broad and narrow \rm H α emission with the continuum suggests that both the UV and optical continuum and the line emission are linked by photoionization. We propose that the distinctive spectral and continuum properties of LRDs can be explained via a viewing angle-dependent nuclear structure in which an optically thick, clumpy gaseous torus surrounds the central accretion disk, with broad-line clouds and absorbers distributed along the less-obscured polar directions.

@article{2026arXiv260604711C, author = {{Chen}, Chang-Hao and {Shangguan}, Jinyi and {Ho}, Luis C. and {Zhang}, Zijian and {Inayoshi}, Kohei and {Li}, Ruancun}, title = {{ABCD: The Nuclear Structure of the Little Red Dots Revealted through Absorption, Break, Continuum, and Decrement}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = jun, eid = {arXiv:2606.04711}, pages = {arXiv:2606.04711}, doi = {10.48550/arXiv.2606.04711}, archiveprefix = {arXiv}, eprint = {2606.04711}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260604711C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, emission lines, jwst, spectroscopy}, month_numeric = {6} }

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General Relativistic Shock Wave Solutions with Black Hole Formation: The Singular Isothermal Sphere Case

Chien-Ting J. Chen, Michael J. Cai, and Fabio Pacucci

arXiv e-prints, Jun 2026

Abs ADS arXiv

The rapid emergence at zrsim 6 of ubiquitous populations of supermassive black holes (SMBHs) revealed by JWST and of quasars with estimated masses M_∙> 10^10 M_⊙demands efficient pathways for early growth. The smooth collapse of a singular isothermal sphere (SIS) has been solved analytically in full general relativity, but the shock waves that inevitably accompany such collapse have not. Here, we derive general- relativistic self-similar shock-wave solutions for the collapse of an SIS to a black hole, extending the framework of Cai amp; Shu (2005) to discontinuous flows. We obtain the general relativistic jump conditions for an isothermal fluid and show that they connect interior collapse solutions to exterior envelopes that may be static, expanding, or collapsing, yielding a rich family of shocks propagating at up to \sim40\% the speed of light; the available exterior types narrow with increasing sound speed. A coordinate- matching technique that uses the zero-velocity surface uniquely bridges the Schwarzschild and comoving self-similar descriptions, completing the characterization of the growing black hole. The central accretion rate is set by the interior collapse alone and is suppressed by a factor of \sim5–7 relative to the smooth expansion-wave solution, while the energy released at the shock reaches \sim10\% of the enclosed rest mass – nearly twice the 5.7\% radiative efficiency of Schwarzschild accretion. These results provide an analytical energy budget for direct-collapse black hole formation, with implications for SMBH seed assembly, the dense cocoons around nascent high-redshift black holes, the recently discovered JWST’s Little Red Dots, and relativistic transients such as gamma-ray bursts.

@article{2026arXiv260629607C, author = {{Chen}, Chien-Ting J. and {Cai}, Michael J. and {Pacucci}, Fabio}, title = {{General Relativistic Shock Wave Solutions with Black Hole Formation: The Singular Isothermal Sphere Case}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, General Relativity and Quantum Cosmology}, year = {2026}, month = jun, eid = {arXiv:2606.29607}, pages = {arXiv:2606.29607}, archiveprefix = {arXiv}, eprint = {2606.29607}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260629607C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, heavy seed, jwst, theory}, month_numeric = {6} }

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Spectral Appearance of Self-gravitating Disks Powered by Stellar Objects: Universal Effective Temperature in the Optical Continuum and Application to Little Red Dots

Yi-Xian Chen, Hanpu Liu, Ruancun Li, and 6 more authors

The Astrophysical Journal Letters, Jun 2026

Abs DOI ADS arXiv

We revisit the spectral appearance of extended self-gravitating accretion disks surrounding compact central objects such as supermassive black holes. Using dust-poor opacities, we show that all optically thick disk solutions possess a universal outer effective temperature of T_eff \ensuremath∼ 4000─4500K, closely resembling compact, high-redshift sources known as little red dots (LRDs). Assuming the extended disk is primarily heated by stellar sources, this “disk Hayashi limit” fixes the dominant optical continuum temperature of the disk spectrum independent of accretion rate Ṁ, central mass M_\ensuremath∙, and disk viscosity \ensuremathα, and removes the parameter-tuning required in previous disk interpretations of LRDs. The formation and accretion of embedded stellar objects can both power the emission of the outer disk and hollow out the inner disk, suppressing variable UV/X-ray associated with a standard quasar. The resulting disk emission is dominated by a luminous optical continuum, while a separate, nonvariable UV component arises from stellar populations on the nuclear to galaxy scale. We map the optimal region of parameter space for such systems and show that LRD-like appearances naturally emerge for Ṁ/\ensuremath\alpha\ensuremath≳0.1M\ensuremath⊙yr-1, a threshold insensitive to M_\ensuremath∙, below which the system may transition into classical non-self- gravitating active galactic nucleus (AGN) disks, potentially a later evolution stage. We expect this transition to be accompanied by the enhancement of metallicity and production of dust, giving rise to far-infrared emission. This picture offers a physically motivated and quantitative framework connecting LRDs with AGNs and their associated nuclear stellar population.

@article{2026ApJ..1003L..46C, author = {{Chen}, Yi-Xian and {Liu}, Hanpu and {Li}, Ruancun and {Wang}, Bingjie and {Ma}, Yilun and {Jiang}, Yan-Fei and {Greene}, Jenny E. and {Quataert}, Eliot and {Goodman}, Jeremy}, title = {{Spectral Appearance of Self-gravitating Disks Powered by Stellar Objects: Universal Effective Temperature in the Optical Continuum and Application to Little Red Dots}}, journal = {\apjl}, keywords = {Galaxy accretion disks, Supermassive black holes, Massive stars, Star formation, Active galactic nuclei, 562, 1663, 732, 1569, 16}, year = {2026}, month = jun, volume = {1003}, number = {2}, eid = {L46}, pages = {L46}, doi = {10.3847/2041-8213/ae6b69}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1003L..46C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2602.06954}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, lrdkeys = {non-agn, sed, theory}, month_numeric = {6} }

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Little Red Dots as Globular Clusters in Formation

John Chisholm, Danielle A. Berg, Michael Boylan-Kolchin, and 7 more authors

The Astrophysical Journal Letters, Jun 2026

Abs DOI ADS arXiv

Little Red Dots (LRDs), among the most enigmatic high-redshift discoveries by JWST, are commonly believed to be powered by accreting supermassive black holes. Here, we explore the possibility that these sources are globular clusters in formation, with rest-frame UV arising from a very young stellar population and rest-frame optical from a short-lived supermassive (>10^4 M_\ensuremath⊙) star. The spectral profiles of LRDs are broadly consistent with this scenario, though the observed temperatures and bolometric luminosities favor emission reprocessed by optically thick continuum-driven winds not fully captured by current models. The LRD z \ensuremath∼ 5\ensuremath-7 UV luminosity function naturally evolves, under standard evolutionary and mass-loss prescriptions, into a present-day mass function with a turnover at log10(M_*/M_\ensuremath⊙) = 5.3 and an exponential cutoff at high masses, consistent with local globular cluster populations. We estimate the total present-day number density of LRDs formed across all redshifts to be ≍0.3 Mpc^\ensuremath-3, similar within uncertainties to local globular clusters. The observed LRD redshift range matches the age distribution of metal-poor globular clusters, without current LRD counterparts to the metal-rich population. If LRDs are globular clusters in formation, we predict chemical abundance patterns characteristic of multiple stellar populations, including enhanced He and N, and potential Na─O and Al─Mg anticorrelations. These results offer a local perspective to explore this surprisingly abundant population of distant sources, and a potential new window into extreme stellar astrophysics in the early Universe.

@article{2026ApJ..1004L...4C, author = {{Chisholm}, John and {Berg}, Danielle A. and {Boylan-Kolchin}, Michael and {de Graaff}, Anna and {Furtak}, Lukas J. and {Kokorev}, Vasily and {Matthee}, Jorryt and {Mu{\textasciitilde n}oz}, Julian B. and {Naidu}, Rohan P. and {Sander}, Andreas A. C.}, title = {{Little Red Dots as Globular Clusters in Formation}}, journal = {\apjl}, keywords = {Globular star clusters, High-redshift galaxies, 656, 734}, year = {2026}, month = jun, volume = {1004}, number = {1}, eid = {L4}, pages = {L4}, doi = {10.3847/2041-8213/ae6dae}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1004L...4C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2602.15935}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {abundance, exotic physics, local counterpart, non-agn, theory}, month_numeric = {6} }

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Primordial-Black-Hole-Based Pathways to Little Red Dots

Valerio De Luca, Loris Del Grosso, Gabriele Franciolini, and 4 more authors

Physical Review Letters, Jun 2026

Abs DOI ADS arXiv

The James Webb Space Telescope has uncovered a population of compact, high-redshift sources, the Little Red Dots (LRDs), which may host supermassive black holes (BHs) significantly heavier than their stellar content compared with local scaling relations. These objects challenge standard models of early galaxy formation and may represent an extreme class of early BH hosts. In this Letter, we investigate whether these BHs could have a primordial origin. We first show that the direct formation of these BH masses in the early Universe is excluded by stringent cosmic microwave background \ensuremathμ-distortion limits. We then investigate the assembly of massive BHs from lighter, observationally allowed primordial black holes (PBHs) via hierarchical mergers, finding that, although this channel can operate depending on the merger history, it faces challenges in explaining the observations due to the rarity of the required high-redshift dark matter halos. Finally, we estimate gas accretion onto intermediate-mass PBHs, while jointly tracking metallicity evolution, and identify regions of parameter space in which such growth could reproduce the observed properties of LRDs. As a special case, we focus on the strongly lensed source QSO1, whose extremely low metallicity and large mass provide a stringent test of these formation channels.

@article{2026PhRvL.136w1402D, author = {{De Luca}, Valerio and {Del Grosso}, Loris and {Franciolini}, Gabriele and {Kritos}, Konstantinos and {Berti}, Emanuele and {D'Orazio}, Daniel J. and {Silk}, Joseph}, title = {{Primordial-Black-Hole-Based Pathways to Little Red Dots}}, journal = {\prl}, keywords = {Cosmology, Astrophysics, and Gravitation}, year = {2026}, month = jun, volume = {136}, number = {23}, eid = {231402}, pages = {231402}, doi = {10.1103/6y1w-87pd}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026PhRvL.136w1402D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2512.19666}, archiveprefix = {arXiv}, primaryclass = {astro-ph.CO}, lrdkeys = {black hole mass, case study, early universe, heavy seed, theory}, month_numeric = {6} }

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Euclid Quick Data Release (Q1): XXIV. Extending the quest for little red dots to z < 4

Euclid Collaboration, L. Bisigello, G. Rodighiero, and 197 more authors

Astronomy & Astrophysics, Jun 2026

Abs DOI ADS arXiv

Recent observations with the James Webb Space Telescope (JWST) have revealed an interesting population of sources with a compact morphology and a characteristic v-shaped continuum, namely blue at a rest frame \ensuremathλ < 4000 Å and red at longer wavelengths. The nature of these sources, which are called little red dots (LRDs), is still highly debated because it is unclear whether they host active galactic nuclei (AGNs) and their number seems to drop drastically at z < 4. We took advantage of the 63 deg^2 covered by the Euclid Quick Data Release (Q1) to extend the search for LRDs to brighter magnitudes and lower redshifts than what was possible with JWST. This is fundamental for a broader view of the evolution of this peculiar galaxy population. The selection was performed by fitting the available photometric data (Euclid, the Spitzer Infrared Array Camera (IRAC), and ground-based griz data) with two power laws to retrieve the rest-frame optical and UV slopes consistently over a wide redshift range (i.e. z < 7.6). We then excluded extended objects and possible line emitters and inspected the data visually to remove any imaging artefacts. The final selection included 3341 LRD candidates from z = 0.33 to z = 3.6, 29 of which were also detected in IRAC. The resulting rest-frame UV luminosity function, in contrast with previous JWST studies, shows that the number density of LRD candidates increases from high redshift to z = 1.5─2.5 and decreases at even lower redshifts. The subsample of more robust LRD candidates that are also detected with IRAC show a weaker evolution, however, which is affected by low statistics and limited by the IRAC resolution. The comparison with previous quasar UV luminosity functions shows that LRDs are not the dominant AGN population at z < 4 and M_UV < \ensuremath-21. Follow-up studies of these LRD candidates are pivotal to confirm their nature, probe their physical properties, and determine whether they are compatible with JWST sources because the different spatial resolution and wavelength coverage of Euclid and JWST might select different samples of compact sources.

@article{2026A&A...711A..24E, author = {{Euclid Collaboration} and {Bisigello}, L. and {Rodighiero}, G. and {Fotopoulou}, S. and {Ricci}, F. and {Jahnke}, K. and {Feltre}, A. and {Allevato}, V. and {Shankar}, F. and {Cassata}, P. and {Dalla Bont{\`a}}, E. and {Gandolfi}, G. and {Girardi}, G. and {Giulietti}, M. and {Grazian}, A. and {Lovell}, C. C. and {Maiolino}, R. and {Matamoro Zatarain}, T. and {Mezcua}, M. and {Prandoni}, I. and {Roberts}, D. and {Roster}, W. and {Salvato}, M. and {Siudek}, M. and {Tarsitano}, F. and {Toba}, Y. and {Vietri}, A. and {Wang}, L. and {Zamorani}, G. and {Baes}, M. and {Belladitta}, S. and {Nersesian}, A. and {Spinoglio}, L. and {Lopez Lopez}, X. and {Aghanim}, N. and {Altieri}, B. and {Amara}, A. and {Andreon}, S. and {Auricchio}, N. and {Aussel}, H. and {Baccigalupi}, C. and {Baldi}, M. and {Balestra}, A. and {Bardelli}, S. and {Basset}, A. and {Battaglia}, P. and {Bender}, R. and {Biviano}, A. and {Bonchi}, A. and {Branchini}, E. and {Brescia}, M. and {Brinchmann}, J. and {Camera}, S. and {Ca{\textasciitilde n}as-Herrera}, G. and {Capobianco}, V. and {Carbone}, C. and {Carretero}, J. and {Casas}, S. and {Castellano}, M. and {Castignani}, G. and {Cavuoti}, S. and {Chambers}, K. C. and {Cimatti}, A. and {Colodro-Conde}, C. and {Congedo}, G. and {Conselice}, C. J. and {Conversi}, L. and {Copin}, Y. and {Courbin}, F. and {Courtois}, H. M. and {Cropper}, M. and {Da Silva}, A. and {Degaudenzi}, H. and {De Lucia}, G. and {Di Giorgio}, A. M. and {Dolding}, C. and {Dole}, H. and {Dubath}, F. and {Duncan}, C. A. J. and {Dupac}, X. and {Dusini}, S. and {Ealet}, A. and {Escoffier}, S. and {Farina}, M. and {Farinelli}, R. and {Faustini}, F. and {Ferriol}, S. and {Finelli}, F. and {Frailis}, M. and {Franceschi}, E. and {Galeotta}, S. and {George}, K. and {Gillard}, W. and {Gillis}, B. and {Giocoli}, C. and {G{\'o}mez-Alvarez}, P. and {Gracia-Carpio}, J. and {Granett}, B. R. and {Grupp}, F. and {Gwyn}, S. and {Haugan}, S. V. H. and {Hoekstra}, H. and {Holmes}, W. and {Hook}, I. M. and {Hormuth}, F. and {Hornstrup}, A. and {Hudelot}, P. and {Jhabvala}, M. and {Keih{\"a}nen}, E. and {Kermiche}, S. and {Kiessling}, A. and {Kubik}, B. and {K{\"u}mmel}, M. and {Kunz}, M. and {Kurki-Suonio}, H. and {Le Boulc'h}, Q. and {Le Brun}, A. M. C. and {Le Mignant}, D. and {Liebing}, P. and {Ligori}, S. and {Lilje}, P. B. and {Lindholm}, V. and {Lloro}, I. and {Mainetti}, G. and {Maino}, D. and {Maiorano}, E. and {Mansutti}, O. and {Marcin}, S. and {Marggraf}, O. and {Martinelli}, M. and {Martinet}, N. and {Marulli}, F. and {Massey}, R. and {Maurogordato}, S. and {Medinaceli}, E. and {Mei}, S. and {Melchior}, M. and {Mellier}, Y. and {Meneghetti}, M. and {Merlin}, E. and {Meylan}, G. and {Mora}, A. and {Moresco}, M. and {Moscardini}, L. and {Nakajima}, R. and {Neissner}, C. and {Niemi}, S.-M. and {Nightingale}, J. W. and {Padilla}, C. and {Paltani}, S. and {Pasian}, F. and {Pedersen}, K. and {Percival}, W. J. and {Pettorino}, V. and {Pires}, S. and {Polenta}, G. and {Poncet}, M. and {Popa}, L. A. and {Pozzetti}, L. and {Raison}, F. and {Rebolo}, R. and {Renzi}, A. and {Rhodes}, J. and {Riccio}, G. and {Romelli}, E. and {Roncarelli}, M. and {Rossetti}, E. and {Rottgering}, H. J. A. and {Rusholme}, B. and {Saglia}, R. and {Sakr}, Z. and {Sapone}, D. and {Sartoris}, B. and {Schewtschenko}, J. A. and {Schirmer}, M. and {Schneider}, P. and {Schrabback}, T. and {Scodeggio}, M. and {Secroun}, A. and {Seidel}, G. and {Serrano}, S. and {Simon}, P. and {Sirignano}, C. and {Sirri}, G. and {Stanco}, L. and {Steinwagner}, J. and {Tallada-Cresp{\'\i}}, P. and {Taylor}, A. N. and {Teplitz}, H. I. and {Tereno}, I. and {Toft}, S. and {Toledo-Moreo}, R. and {Torradeflot}, F. and {Tutusaus}, I. and {Valenziano}, L. and {Valiviita}, J. and {Vassallo}, T. and {Verdoes Kleijn}, G. and {Veropalumbo}, A. and {Wang}, Y.}, title = {{Euclid Quick Data Release (Q1): XXIV. Extending the quest for little red dots to z < 4}}, journal = {\aap}, keywords = {galaxies: active, galaxies: evolution, galaxies: luminosity function, mass function}, year = {2026}, month = jun, volume = {711}, eid = {A24}, pages = {A24}, doi = {10.1051/0004-6361/202554537}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...711A..24E}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, catalog, non-jwst, photometry, sample selection}, eprint = {2503.15323}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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The discovery of two little red dots in transition into quasars

Shuqi Fu, Zijian Zhang, Danyang Jiang, and 9 more authors

Nature Astronomy, Jun 2026

Abs DOI ADS arXiv

JWST has uncovered a population of compact objects that show a unique V-shaped spectral energy distribution in the ultraviolet and optical wavelength range. These so-called little red dots (LRDs) often exhibit broad Balmer emission lines, indicative of the presence of active galactic nuclei (AGNs). They generally lack detection of X-ray, radio and mid-infrared radiation, which is fundamentally different from typical AGNs. Various models, including super-Eddington-accreting black holes enshrouded in dense and dust-poor gas, have been proposed to explain these features. However, the nature of LRDs remains debated and their evolutionary fate is unclear. Here we report two unusual LRDs at redshifts of 2.871 and 2.930 that are in a transitional phase towards typical AGNs. Their V-shaped spectral energy distributions, compact optical morphology and broad emission lines satisfy the defining criteria of LRDs. However, they exhibit intense X-ray, radio and mid-infrared radiation that is much stronger than previously known LRDs. These hybrid properties suggest that the dense gas envelope around their central black holes is dispersing, allowing high-energy photons and radio emission to escape. Meanwhile, a dust torus is forming. This finding provides a direct insight into the nature of LRDs and indicates that at least some LRDs will evolve into AGNs or quasars at later times.

@article{2026NatAs.tmp..118F, author = {{Fu}, Shuqi and {Zhang}, Zijian and {Jiang}, Danyang and {Chen}, Jie and {Jiang}, Linhua and {Ho}, Luis C. and {Inayoshi}, Kohei and {Chen}, Kaiyuan and {Lyu}, Jianwei and {Sun}, Fengwu and {Wang}, Feige and {Yang}, Jinyi}, title = {{The discovery of two little red dots in transition into quasars}}, journal = {Nature Astronomy}, year = {2026}, month = jun, doi = {10.1038/s41550-026-02885-8}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026NatAs.tmp..118F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2512.02096}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {agn-dominated, case study, multi-wavelength, radio, x-ray}, month_numeric = {6} }

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The quasi-star model for Little Red Dots: potential and challenges

Fabrizio Gentile, Mauro Giavalisco, Emanuele Daddi, and 25 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

(Abridged) Little Red Dots (LRDs) are a class of sources discovered by JWST observationally defined by a “V-shaped” rest-frame UV- Optical SED, a compact or unresolved morphology, and for having, frequently, broad hydrogen emission lines. Among various models, those involving a quasi-star interpret LRDs as an intermediate stage in the evolution of a super-massive black hole (SMBH) seed into a classic AGN. In this paper, we employ the radiative- transfer code \textbackslashtexttt{Cloudy} to study whether this model is able to reproduce the spectral features commonly observed in LRDs. The model consists of an accreting SMBH (M_\rm BH\sim10^5-6 M_⊙) surrounded by a convective layer where a black-body (BB) spectrum with T\sim5000 \rm K and L\sim10^44.4 \rm erg s^-1 is produced. This BB is then reprocessed by a concentric thick (ΔR\sim1000 \rm AU) shell of dense (n_\rm H\sim10^11 \rm cm^-3) gas partially ionised by thermal collisions. The emerging radiation is further reprocessed by a diffuse clumpy medium surrounding the quasi-star. We fit this model to JWST/NIRSpec spectra of LRDs from the literature, deriving the main physical parameters and the SMBH masses. Once coupled with the UV emission from a host galaxy, this model is able to reproduce the shape of the UV-to-NIR continuum, including the presence of a Balmer break, as well as the luminosity of the hydrogen emission lines. However, this quasi-star model does not natively account for the presence of broad helium lines and for the possible presence of hot dust, needing additional components to match these observables. Our main result is to show how some LRDs can be modeled as quasi-stars, highlighting that a significant degeneracy exists among different LRD models. This has important consequences for our understanding of the mechanisms driving black hole growth in the early Universe.

@article{2026arXiv260606575G, author = {{Gentile}, Fabrizio and {Giavalisco}, Mauro and {Daddi}, Emanuele and {Elbaz}, David and {Billand}, Jean-Baptiste and {Franco}, Maximilen and {Magnelli}, Benjamin and {Barro}, Guillermo and {Cheng}, Yingjie and {Cleri}, Nikko J. and {Davis}, Kelcey and {Delvecchio}, Ivan and {Dickinson}, Mark and {Finkelstein}, Steven L. and {Gandolfi}, Giovanni and {Hirschmann}, Michaela and {Hu}, Weida and {Kocevski}, Dale and {Koekemoer}, Anton M. and {Lucas}, Ray and {Mascia}, Sara and {Napolitano}, Lorenzo and {Papovich}, Casey and {P{\'e}rez-D{\'\i}az}, Borja and {Perez-Gonzalez}, Pablo and {Trump}, Jonathan R. and {Wang}, Xin and {Yung}, L. Y. Aaron}, title = {{The quasi-star model for Little Red Dots: potential and challenges}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.06575}, pages = {arXiv:2606.06575}, archiveprefix = {arXiv}, eprint = {2606.06575}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260606575G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, exotic physics, jwst, sed, simulation}, month_numeric = {6} }

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VENUS: When red meets blue: A multiply imaged little red dot with an apparent blue companion behind the galaxy cluster Abell 383

Miriam Golubchik, Lukas J. Furtak, Joseph F. V. Allingham, and 50 more authors

Astronomy & Astrophysics, Jun 2026

Abs DOI ADS arXiv

We report the discovery of a doubly imaged little red dot (LRD) candidate behind the galaxy cluster Abell 383, which we dub A383-LRD1. Initially classified as a dropout galaxy in HST imaging with several ground-based emission line detections placing it at z_spec = 6.027, new JWST/NIRCam observations taken as part of the cycle 4 VENUS survey now reveal that the source consists of two underlying components. These consist of a red point-source with a V-shaped SED consistent with LRD selection criteria and a nearby (\ensuremath∼380 pc) compact blue companion, which was the main contributor to the previous rest-frame UV detections. Based on lensing symmetry and its SED, the LRD appears to lie at a similar redshift as well. The magnification of the two images of A383-LRD1 is \ensuremathμ_A = 16.2 \ensuremath\pm 1.2 and \ensuremathμ_B = 9.0 \ensuremath\pm 0.6, respectively, and the predicted time delay between them is \ensuremath∆t_grav = 5.20 \ensuremath\pm 0.14 yr (\ensuremath∼0.7 yr in the rest-frame). After correcting for the lensing magnification, we derived an absolute magnitude of M_UV, LRD = \ensuremath-16.8 \ensuremath\pm 0.3 for the LRD and M_UV, BC = \ensuremath-18.2 \ensuremath\pm 0.2 for the blue companion. We performed SED fits to both components, revealing the LRD to show the best fit with a black hole star (BH*) model and a substantial host galaxy, along with the blue companion with an extremely young, emission-line dominated star-forming nebula. If it is verified spectroscopically in the future, A383-LRD1 would represent the second known multiply imaged LRD detected to date, following A2744-QSO1. To our knowledge, it would also stand as the first LRD system with a confirmed detection of [C II]\ensuremathλ158 \ensuremathμm emission from ALMA observations. Thanks to the lensing magnification, this system opens a unique door to studying the relation between a LRD, its host galaxy, and its environment. It represents a prime candidate for deep JWST spectroscopy and high-resolution ALMA follow-up observations.

@article{2026A&A...710A.226G, author = {{Golubchik}, Miriam and {Furtak}, Lukas J. and {Allingham}, Joseph F. V. and {Zitrin}, Adi and {Akins}, Hollis B. and {Kokorev}, Vasily and {Fujimoto}, Seiji and {Abdurro'uf} and {Amor{\'\i}n}, Ricardo O. and {Bauer}, Franz E. and {Bezanson}, Rachel and {Brada{\v{c}}}, Marusa and {Bradley}, Larry D. and {Brammer}, Gabriel B. and {Chisholm}, John and {Coe}, Dan and {Conselice}, Christopher J. and {Dayal}, Pratika and {Dessauges-Zavadsky}, Miroslava and {Diego}, Jose M. and {Faisst}, Andreas L. and {Fei}, Qinyue and {Ferguson}, Henry C. and {Finkelstein}, Steven L. and {Frye}, Brenda L. and {Gonz{\'a}lez-Otero}, Mauro and {Greene}, Jenny E. and {Harikane}, Yuichi and {Hsiao}, Tiger Yu-Yang and {Inayoshi}, Kohei and {Jim{\'e}nez-Teja}, Yolanda and {Knudsen}, Kirsten and {Koekemoer}, Anton M. and {Labb{\'e}}, Ivo and {Lucas}, Ray A. and {Magdis}, Georgios E. and {Matthee}, Jorryt and {Messa}, Matteo and {Naidu}, Rohan P. and {Nakane}, Minami and {Noirot}, Ga{\"e}l and {Pan}, Richard and {Papovich}, Casey and {Richard}, Johan and {Ricotti}, Massimo and {Robbins}, Luke and {Stark}, Daniel P. and {Sun}, Fengwu and {Treu}, Tommaso and {Tripodi}, Roberta and {Vanzella}, Eros and {Willott}, Chris and {Windhorst}, Rogier A.}, title = {{VENUS: When red meets blue: A multiply imaged little red dot with an apparent blue companion behind the galaxy cluster Abell 383}}, journal = {\aap}, keywords = {gravitational lensing: strong, galaxies: high-redshift, quasars: general}, year = {2026}, month = jun, volume = {710}, eid = {A226}, pages = {A226}, doi = {10.1051/0004-6361/202558407}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...710A.226G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2512.02117}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {alma, case study, host galaxy, jwst, sed}, month_numeric = {6} }

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JWST’s Little Red Dots as collapsed Supermassive Dark Stars

Cosmin Ilie

arXiv e-prints, Jun 2026

Abs DOI ADS arXiv

The nature of the “Little Red Dots” (LRDs) is one of the most profound mysteries posed by the JWST data. One promising class of models that can reproduce the observed LRDs spectra and morphology are quasi-stars: massive envelopes surrounding accreting black holes formed via the collapse of supermassive stars (SMSs). However, the canonical SMS pathway relies on a highly restricted set of environmental and structural conditions: strong Lyman–Werner (LW) backgrounds to suppress H_2 cooling, high and sustained gas inflow rates to enforce entropy stratified envelopes, and assume non-zero rotational support in order to prevent GR instability collapse before ∼10^6 M_⊙. Here we show that supermassive dark stars (SMDSs), powered by dark matter (DM) annihilation rather than nuclear burning, naturally satisfy the key structural and energetic requirements for quasi-star (QS) formation while relaxing {\textbackslashit all} of those restrictive conditions listed above. Moreover, quasi-stars formed through the SMDS pathway are born with prompt BH masses (rsim 10%) of the progenitor mass. They therefore enter directly into a late-stage quasi-star regime; subsequently the envelope expands and cools until its photosphere reaches the zero-metallicity opacity limit (T_\rm eff\sim3000-6000\,\rm K). Those cool, optically thick, unresolved photospheres can reproduce key features of many JWST LRDs.

@article{2026arXiv260602539I, author = {{Ilie}, Cosmin}, title = {{JWST's Little Red Dots as collapsed Supermassive Dark Stars}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology}, year = {2026}, month = jun, eid = {arXiv:2606.02539}, pages = {arXiv:2606.02539}, doi = {10.48550/arXiv.2606.02539}, archiveprefix = {arXiv}, eprint = {2606.02539}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260602539I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {exotic physics, heavy seed, jwst, theory}, month_numeric = {6} }

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JADES: the mass-metallicity relation at z=1-10. New calibrations, extremely metal-poor galaxies, and chemical diversity

Yuki Isobe, Mirko Curti, Roberto Maiolino, and 28 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

We present gas-phase metallicities of star-forming galaxies at z=1-10 with deep JWST/NIRSpec spectra from the JADES full data release, Dark Horse, and OASIS programmes. We stack \sim1500 medium- resolution spectra, yielding detections of the [OIII]λ4363 auroral line down to 12+\log(\mathrmO/H)=7.0 to derive stack-based strong-line calibrations over the metallicity range 12+\log(\mathrmO/H)=7.0-8.7. At a fixed metallicity, our stacks exhibit [OIII]λ5007/Hβ and [OIII]λ5007/[OII]λλ3726,3729 values generally lower than calibrations based on high-z individual auroral-line emitters, suggesting an observational bias towards higher excitation introduced when requiring auroral line detections in individual spectra. Based on our new calibrations, we obtain canonical mass-metallicity relations (MZRs) at z=1-10, identifying a decrease in metallicities from z\sim0 to z\sim4-10, without significant change in slope. Moreover, we identify 50 promising candidates of extremely metal-poor galaxies (EMPGs) with 12+\log(\mathrmO/H)=6.7-7.3 (1-4\% solar metallicity) at z=1.2-9.1. The MZRs of EMPGs are characterised by a large scatter, with those having lower metallicities generally exhibiting lower sSFRs, opposite of what expected from the local Fundamental Metallicity Relation. These results support a stochastic star-formation history involving gas consumption/ejection and metal-poor inflow, strongly affecting metallicities of low-mass galaxies. Furthermore, we identify two Little Red Dots in our EMPG candidates, both exhibiting broad Hα and prominent Lyα, offering insights into the early black-hole growth in extremely metal-poor environments.

@article{2026arXiv260611345I, author = {{Isobe}, Yuki and {Curti}, Mirko and {Maiolino}, Roberto and {Duan}, Qiao and {McClymont}, William and {Pusk{\'a}s}, D{\'a}vid and {D'Eugenio}, Francesco and {Rinaldi}, Pierluigi and {Trussler}, James A. A. and {Scholtz}, Jan and {Looser}, Tobias J. and {Nelson}, Erica and {Ji}, Xihan and {Langeroodi}, Danial and {Tacchella}, Sandro and {Jones}, Gareth C. and {Juod{\v{z}}balis}, Ignas and {Pascalau}, Robert G. and {Hsiao}, Tiger Yu-Yang and {{\"U}bler}, Hannah and {Baker}, William M. and {Bunker}, Andrew J. and {Carniani}, Stefano and {Charlot}, St{\'e}phane and {Curtis-Lake}, Emma and {Geris}, Sophia and {Koller}, Maria and {Lyu}, Jianwei and {Robertson}, Brant and {Williams}, Christina C. and {Wu}, Zihao}, title = {{JADES: the mass-metallicity relation at $z=1-10$. New calibrations, extremely metal-poor galaxies, and chemical diversity}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.11345}, pages = {arXiv:2606.11345}, archiveprefix = {arXiv}, eprint = {2606.11345}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260611345I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, host galaxy, jwst, spectroscopy}, month_numeric = {6} }

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The Cliff: A Metal-Poor Little Red Dot Hosting an Overmassive Black Hole at z = 3.55

L. R. Ivey, F. D’Eugenio, R. Maiolino, and 18 more authors

Monthly Notices of the Royal Astronomical Society, Jun 2026

Abs DOI ADS arXiv

JWST has revealed a large population of massive black holes (BHs) in the early Universe with unusual properties which mark them as distinct from low-redshift active galactic nuclei. Such findings have prompted the development of new models of BH formation and growth, and of their co-evolution with host galaxies. Linking the gas-phase metallicity of BH environments to seed masses is key to understanding which evolutionary pathways could explain the population of JWST-discovered BHs. We present new high- resolution JWST NIRSpec/IFU observations covering the rest-frame optical emission lines of a Little Red Dot (LRD) at z = 3.55, known as The Cliff, from the ’Red Unknowns: Bright Infrared Extragalactic Survey’ (RUBIES). We find evidence for low metallicity (Z = 0.016 \ensuremath\pm 0.003 Z_\ensuremath⊙) based on the low narrow-line [O III]\ensuremathλ5007/H\ensuremathβ ratio, supported by the non-detection of low-ionisation emission lines such as [O II]\ensuremathλ\ensuremathλ3727,3729 and [N II]\ensuremathλ\ensuremathλ6548,6583. We find that the observed properties of The Cliff, including its overmassive BH, can be reproduced by some simulations of black hole growth and evolution down to z \raisebox-0.5ex~3.5. However, such outcomes require high seed masses (10^4 - 10^5 M_\ensuremath⊙) and appear rarely within a simulation volume comparable to the 3 < z < 4 RUBIES volume, highlighting the unusual nature of The Cliff. Future simulations and numerical models will help to uncover how such a metal-poor system managed to develop a massive black hole and persist to such low redshift.

@article{2026MNRAS.tmp.1141I, author = {{Ivey}, L. R. and {D'Eugenio}, F. and {Maiolino}, R. and {Isobe}, Y. and {Juod{\v{z}}balis}, I. and {Koudmani}, S. and {Perna}, M. and {Zhang}, S. and {Bromm}, V. and {Bunker}, A. J. and {Carniani}, S. and {Fabian}, A. C. and {Inayoshi}, K. and {Ji}, X. and {Jones}, G. C. and {Liu}, B. and {Pascalau}, R. and {Rinaldi}, P. and {Robertson}, B. and {Scholtz}, J. and {Tacchella}, S.}, title = {{The Cliff: A Metal-Poor Little Red Dot Hosting an Overmassive Black Hole at z = 3.55}}, journal = {\mnras}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, doi = {10.1093/mnras/stag1220}, archiveprefix = {arXiv}, eprint = {2604.09177}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.tmp.1141I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {case study, emission lines, heavy seed, jwst, simulation}, month_numeric = {6} }

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Compact Core, Extended Reach: A Bipolar kpc-Scale Elongation in a Little Red Dot at z ≈5.5

Zhiyuan Ji, Yang Sun, Mauro Giavalisco, and 7 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Little Red Dots (LRDs) appear extremely compact at rest-frame optical wavelengths, yet many show extended rest-frame UV morphology revealing more complex internal structure. We present a combined analysis of VLT/MUSE rest-frame UV integral-field spectroscopy and continuum-subtracted [O III], Hβ, and Hα+[N II] emission-line maps from JWST/NIRCam imaging at sub-kpc resolution for LRD-204851 at z=5.482 in GOODS-S. We find that LRD-204851 hosts a remarkably thin, bipolar, elongated structure passing through the optical continuum centroid and extending several kpc on either side, traced by both the UV continuum and the rest-frame optical emission lines, with a bright [O III] clump-like structure \sim2 kpc to the south-east of the centroid. The MUSE observations reveal a double-peaked Lyα profile, with a broad and bright near-systemic red peak and a relatively faint peak blueshifted by \sim430 km s^-1, accompanied by a tentative N V λ1238 detection at similar velocity. In narrow-band imaging extracted from the MUSE IFU cube, both the blue Lyα peak and the tentative N V emission lean toward this same south-eastern direction. Independently, radiative-transfer modeling of the integrated Lyα profile favors a biconical low-column-density cavity in a dense, slowly expanding neutral envelope, in support of the bipolar geometry traced by the line maps. Together, these results suggest that the elongated emission of LRD-204851 is connected to radiation and/or gas flow from its central engine through a low-column- density channel with a small opening angle that may trace either a slow outflow or a quasi-static ionization cone. LRD-204851 is one of the first LRDs where the central engine’s impact on its host galaxy is potentially directly observable on kpc scales.

@article{2026arXiv260618342J, author = {{Ji}, Zhiyuan and {Sun}, Yang and {Giavalisco}, Mauro and {Zhu}, Yongda and {Rieke}, George H. and {Williams}, Christina C. and {Maseda}, Michael V. and {Lyu}, Jianwei and {Rieke}, Marcia and {Tacchella}, Sandro}, title = {{Compact Core, Extended Reach: A Bipolar kpc-Scale Elongation in a Little Red Dot at $z \approx 5.5$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.18342}, pages = {arXiv:2606.18342}, archiveprefix = {arXiv}, eprint = {2606.18342}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260618342J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {case study, emission lines, jwst, kinematics, morphology}, month_numeric = {6} }

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Through the Veil: Lyα Illuminates the Host Galaxies of Little Red Dots

Zhiyuan Ji, Yang Sun, Mauro Giavalisco, and 5 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Little Red Dots (LRDs) are enigmatic, compact red sources ubiquitous in JWST deep fields whose physical nature remains elusive. As one of the most sensitive tracers of neutral hydrogen in galaxy environments, Lyα is uniquely positioned to probe the gaseous structures proposed to explain LRDs’ unusual properties. We present a systematic study of Lyα emission in LRDs, using a sample of 110 spectroscopically confirmed LRDs at z ≥4 from the A. de Graaff et al. (2025) catalog, all with NIRSpec/PRISM coverage of the Lyα line. We detect Lyα at signal-to-noise S/N ≥3 in 32 LRDs, finding Lyα luminosities and the distribution of rest-frame equivalent widths consistent with normal star-forming galaxies at comparable redshifts. Yet the Lyα/Hα ratios fall systematically below those of star-forming galaxies, and the Lyα luminosity tracks [O III] luminosity more closely than [O III] equivalent width, together suggesting that Lyα is primarily associated with the host-scale component rather than the compact component responsible for the broad Balmer lines and red continuum. For 13 LRDs at z rsim 5.5, we construct continuum-subtracted Lyα maps using broadband imaging from HST/ACS or JWST/NIRCam, revealing spatially extended, asymmetric, and often offset emission relative to the rest- optical light, consistent with resonant scattering through clumpy, anisotropic gas commonly observed in high-redshift Lyα emitters. These results support a two-component picture in which the compact rest-optical source is embedded within a more extended host-galaxy environment whose interstellar and circumgalactic gas shapes Lyα escape and spatial redistribution. Lyα opens a new window into the relation between the compact red component, the host galaxy, and the surrounding gas in LRDs.

@article{2026arXiv260609970J, author = {{Ji}, Zhiyuan and {Sun}, Yang and {Giavalisco}, Mauro and {de Graaff}, Anna and {Williams}, Christina C. and {Zhu}, Yongda and {Rieke}, George H. and {Rieke}, Marcia}, title = {{Through the Veil: Ly$α$ Illuminates the Host Galaxies of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.09970}, pages = {arXiv:2606.09970}, archiveprefix = {arXiv}, eprint = {2606.09970}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260609970J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, host galaxy, jwst, spectroscopy}, month_numeric = {6} }

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Little Red Dots at z\raisebox-0.5ex\textasciitilde2 in EIGER reveal a gentle decline with respect to their peak number density at z\raisebox-0.5ex\textasciitilde5

Shrriya Kapoor, Jorryt Matthee, Alberto Torralba, and 10 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

We report the discovery of a sample of little red dots (LRDs) at z ≈2 identified from deep JWST/NIRCam imaging and wide- field slitless spectroscopy over 140 arcmin^2 from the EIGER survey. With an improved blind broad-line identification algorithm, we select 19 sources at spectroscopic redshifts z = 1.55-3.18 identified via rest-frame near-infrared lines (Paschen-β, HeI+Paγ and OI). Based on a range of spectro- photometric criteria, we classify five of these sources as LRDs and the other 14 as classical active galactic nuclei (AGNs). This classification is corroborated by some X-ray detections among the AGNs. Classical AGNs dominate the number counts above optical luminosities M_5100<-22.5, whereas the LRD fraction among broad-line sources reaches 100 % at M_5100≈-20. The LRDs span the range in Balmer break strengths seen in the higher redshift populations. Blue-shifted HeI absorption is detected in the two reddest sources. The HeI/Paγ ratio cleanly separates LRDs from classical AGNs and seems to anti-correlate with Balmer break strength, likely tracing HeI self-absorption at higher gas column densities. Our LRD sample has a similar optical luminosity range as their high-redshift counterparts, corresponding to black hole masses of \sim10^6 M_⊙ at the Eddington luminosity. We measure LRD number densities of ≈7\times10^-6 cMpc^-3 at z = 1.9-2.5, which indicates that LRDs represent ≲3 % of the AGN population at these epochs. Our results confirm the previously reported decline in the LRD number density with respect to z ≈5 based on photometric surveys, although we find the decline to be more gentle than earlier emphasized.

@article{2026arXiv260700084K, author = {{Kapoor}, Shrriya and {Matthee}, Jorryt and {Torralba}, Alberto and {Kramarenko}, Ivan G. and {Bordoloi}, Rongmon and {Greene}, Jenny E. and {Iani}, Edoardo and {Kashino}, Daichi and {Liu}, Zhaoran and {Mackenzie}, Ruari and {Mascia}, Sara and {Naidu}, Rohan P. and {Simcoe}, Rob}, title = {{Little Red Dots at z\raisebox{-0.5ex}\textasciitilde2 in EIGER reveal a gentle decline with respect to their peak number density at z\raisebox{-0.5ex}\textasciitilde5}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = jun, eid = {arXiv:2607.00084}, pages = {arXiv:2607.00084}, archiveprefix = {arXiv}, eprint = {2607.00084}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260700084K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, black hole mass, emission lines, jwst, spectroscopy}, month_numeric = {6} }

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Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies

Atte Keitaanranta, Peter H. Johansson, Alexander Rawlings, and 5 more authors

Monthly Notices of the Royal Astronomical Society, Jun 2026

Abs DOI ADS arXiv

We present a cosmological zoom-in simulation targeting the high-redshift compact progenitor phase of massive galaxies, with the most massive galaxy reaching a stellar mass of at . The dynamics of supermassive black holes (SMBHs) is modelled from seeding down to their coalescence at sub-parsec scales due to gravitational wave (GW) emission by utilizing a new version of the KETJU code, which combines regularized integration of sufficiently massive SMBHs with a dynamical friction subgrid model for lower mass SMBHs. All nine massive galaxies included in this study go through a gas-dominated phase of early compaction in the redshift range of , starting at stellar masses of and ending at a few times . The sizes, masses, and broad-band fluxes of these compact systems are in general agreement with the population of systems observed with James Webb Space Telescope known as ’Little Red Dots’. In the compact phase, the stellar and SMBH masses grow rapidly, leading to a sharp decline in the central gas fractions. The outer regions, however, remain relatively gas-rich, leading to subsequent off-centre star formation and size growth. Due to the very high central stellar densities (), the SMBHs merge rapidly, typically just after the SMBH binaries have become bound. Combining KETJU with the phenomenological PhenomD model resolves the complete evolution of the GW emission from SMBH binaries through the pulsar timing array frequency waveband up to the final few orbits that produce GWs observable with the future Laser Interferometer Space Antenna mission.

@article{2026MNRAS.549ag756K, author = {{Keitaanranta}, Atte and {Johansson}, Peter H. and {Rawlings}, Alexander and {Tuominen}, Toni and {Rantala}, Antti and {Naab}, Thorsten and {Liao}, Shihong and {Reinoso}, Basti{\'a}n}, title = {{Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies}}, journal = {\mnras}, keywords = {gravitation, methods: numerical, galaxies: evolution, galaxies: interactions, quasars: supermassive black holes, Astrophysics of Galaxies}, year = {2026}, month = jun, volume = {549}, number = {1}, eid = {stag756}, pages = {stag756}, doi = {10.1093/mnras/stag756}, archiveprefix = {arXiv}, eprint = {2512.11665}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.549ag756K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, morphology, simulation}, month_numeric = {6} }

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The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot

Vasily Kokorev, John Chisholm, Rohan P. Naidu, and 19 more authors

The Astrophysical Journal, Jun 2026

Abs DOI ADS arXiv

The detection of strong Balmer breaks and absorption features in Little Red Dots (LRDs) suggests they host active galactic nuclei embedded within dense gas envelopes, potentially powered by super-Eddington accretion. We present GLIMPSE-17775, a luminous (L_bol \ensuremath∼ 10^45 erg s^\ensuremath-1) LRD at z = 3.501 behind Abell S1063 (\ensuremathμ \ensuremath∼ 2), observed with deep JWST/NIRCam and a \ensuremath∼20 hr (80 hr delensed) NIRSpec G395M spectrum. The data reveal over 40 emission and absorption features, including a rich forest of low-ionization Fe II lines and numerous broad hydrogen recombination transitions. We use this depth to test the dense-gas interpretation through five independent diagnostics. Nearly all permitted lines show exponential wings with consistent FWHM, a signature of Thomson scattering requiring n_e \ensuremath≳ 10^8 cm^\ensuremath-3. Adopting this width yields M_BH \ensuremath∼ 10^6.7M_\ensuremath⊙, a factor of 10 lower than Gaussian fits, and \ensuremathλ_Edd \ensuremath∼ 1.8. Additional diagnostics support the same picture: a pronounced Balmer break (f_\ensuremathν,4050/f_\ensuremathν,3670 = 2.0 \ensuremath\pm 0.1), enhanced He I \ensuremathλ7065 and \ensuremathλ10830 with P-Cygni absorption, Bowen-fluorescent O I \ensuremathλ8446─\ensuremathλ11290 emission requiring Ly\ensuremathβ pumping, and 16 Fe II lines matching fluorescence models. These features indicate a dense (n \ensuremath∼ 10^8 cm^\ensuremath-3), partially ionized cocoon where scattering and fluorescence dominate line formation, providing strong evidence that at least some LRDs are powered by super-Eddington black hole growth in the early Universe.

@article{2026ApJ..1004..153K, author = {{Kokorev}, Vasily and {Chisholm}, John and {Naidu}, Rohan P. and {Fujimoto}, Seiji and {Atek}, Hakim and {Brammer}, Gabriel and {Finkelstein}, Steven L. and {Akins}, Hollis B. and {Berg}, Danielle A. and {Furtak}, Lukas J. and {Fei}, Qinyue and {Hsiao}, Tiger Yu-Yang and {Labb{\'e}}, Ivo and {Matthee}, Jorryt and {Mu{\textasciitilde n}oz}, Julian B. and {Oesch}, Pascal A. and {Pan}, Richard and {Rinaldi}, Pierluigi and {Saldana-Lopez}, Alberto and {Schaerer}, Daniel and {Volonteri}, Marta and {Zitrin}, Adi}, title = {{The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot}}, journal = {\apj}, keywords = {Black holes, Active galactic nuclei, Galaxy evolution, 162, 16, 594}, year = {2026}, month = jun, volume = {1004}, number = {2}, eid = {153}, pages = {153}, doi = {10.3847/1538-4357/ae4ed7}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1004..153K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2511.07515}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {agn-dominated, case study, jwst, spectroscopy, super-eddington}, month_numeric = {6} }

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From Nuclear Star Clusters to Little Red Dots: Black Hole Growth, Mergers, and Tidal Disruptions

Konstantinos Kritos and Joseph Silk

The Astrophysical Journal, Jun 2026

Abs DOI ADS arXiv

Little Red Dots, discovered by the James Webb Space Telescope, are hypothesized to be active galactic nuclei containing a supermassive black hole, possibly surrounded by a dense stellar cluster, large amounts of gas, and likely by a population of stellar-mass black holes. We develop a simple nuclear star cluster model to evolve the rapid mass growth of black hole seeds into the supermassive regime. The combined processes of tidal disruption events, black hole captures, and gas accretion are accounted for self-consistently in our model. Given the observed number density of Little Red Dots, and under reasonable assumptions, we predict at least a few tens of tidal disruption events and at least a few black hole captures at z = 4─6, with a tidal disruption event rate an order of magnitude larger than the black hole capture rate. We also estimate the uncertainties in these estimates. Finally, we comment on the low X-ray luminosity of Little Red Dots.

@article{2026ApJ..1004..226K, author = {{Kritos}, Konstantinos and {Silk}, Joseph}, title = {{From Nuclear Star Clusters to Little Red Dots: Black Hole Growth, Mergers, and Tidal Disruptions}}, journal = {\apj}, keywords = {Star clusters, Active galactic nuclei, Supermassive black holes, James Webb Space Telescope, Tidal disruption, 1567, 16, 1663, 2291, 1696}, year = {2026}, month = jun, volume = {1004}, number = {2}, eid = {226}, pages = {226}, doi = {10.3847/1538-4357/ae731c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1004..226K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, early universe, heavy seed, theory, x-ray}, eprint = {2510.21709}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, month_numeric = {6} }

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No evolution in the number density of little red dots from cosmic dawn to cosmic noon

Federica Loiacono, Roberto Gilli, Marco Mignoli, and 24 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

We present our search for little red dots (LRDs) in the “J1030 field”, a region of the sky around the z∼6.3 quasar SDSS J1030+0524, observed by the JWST EIGER program. Over 154 point- like sources selected in a JWST-based photometric catalog, we find five broad line emitters (with FWHM rsim 1000 \rm km s^-1) that are red (F200W - F356W > 0) and are undetected in the X-rays. We use these sources to derive the bolometric luminosity function (LF) of LRDs at z = 2.4 and z = 4.5. At z = 2.4, the space density of LRDs is only a factor of ∼2 lower than that of all pre-JWST active galactic nuclei (AGNs) with bolometric luminosity L_\rm bol rsim 3 \times 10^44 \rm erg s^-1. At z = 4.5, our estimate is consistent with those derived for LRDs based on larger areas of the sky. A similar behaviour is observed in the black hole mass function. More importantly, we study the number density of LRDs from cosmic dawn to cosmic noon. We find that there is no significant evolution in the abundance of LRDs with L_\rm bol rsim 3 \times 10^44 \rm erg s^-1 at z > 2. We speculate that the drop at z < 4 seen by other studies is due to their sampling of only the bright-end of the LRDs LF. At cosmic noon, the abundance of LRDs is n = 3.4^+5.6_-2.4 \times 10^-5 \rm Mpc^-3, which is a factor of ∼350 larger than recent model predictions and is comparable with that of X-ray selected AGNs with similar bolometric luminosity. Our result may imply that, if LRDs are the early, rapid stages of supermassive black hole growth, as suggested by some models, then the formation of black hole seeds can be efficient down to epochs as recent as cosmic noon. Alternatively, LRDs may simply be a high- accretion phase in already mature black holes.

@article{2026arXiv260630253L, author = {{Loiacono}, Federica and {Gilli}, Roberto and {Mignoli}, Marco and {Brusa}, Marcella and {Calura}, Francesco and {Chiaberge}, Marco and {Comastri}, Andrea and {D'Amato}, Quirino and {Decarli}, Roberto and {Delvecchio}, Ivan and {Iwasawa}, Kazushi and {Juod{\v{z}}balis}, Ignas and {Lanzuisi}, Giorgio and {Maiolino}, Roberto and {Marchesi}, Stefano and {Mazzolari}, Giovanni and {Norman}, Colin and {Peca}, Alessandro and {Prandoni}, Isabella and {Sapori}, Matteo and {Signorini}, Matilde and {Tozzi}, Paolo and {Vanzella}, Eros and {Vignali}, Cristian and {Vito}, Fabio and {Zamorani}, Gianni and {Zanella}, Anita}, title = {{No evolution in the number density of little red dots from cosmic dawn to cosmic noon}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2026}, month = jun, eid = {arXiv:2606.30253}, pages = {arXiv:2606.30253}, archiveprefix = {arXiv}, eprint = {2606.30253}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260630253L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, black hole mass, early universe, jwst, x-ray}, month_numeric = {6} }

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Aether-SHELLQs: JWST integral-field spectroscopy of candidate obscured quasars at z \raisebox-0.5ex~6

Yoshiki Matsuoka, Roberto Decarli, Emanuele Paolo Farina, and 12 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

We present James Webb Space Telescope (JWST) NIRSpec integral field unit (IFU) observations of six galaxies at z ∼6, obtained as part of the Aether project (General Observers program 5645). The targets were originally identified by the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) survey, as candidate obscured quasars with luminous (rsim10^43 erg s^-1) but narrow (\lesssim500 km s^-1) Lyα emission. Two objects exhibit a broad component in their Balmer lines (FWHM >3000 km s^-1), indicating the presence of active galactic nuclei (AGNs), while the remaining four show similar profiles in permitted and forbidden lines. Combining these data with similar SHELLQs objects reported previously, we find that the presence of broad lines is strongly correlated with Lyα luminosity (L_\rm Lyα); the inferred AGN fraction is >77 % and <15 % above and below L_\rm Lyα =10^44 erg s^-1, respectively. Dust-extinction corrections inferred from the Balmer decrement would imply unrealistically high Lyα luminosities, suggesting that the line-emitting gas consists of multiple zones. The IFU data reveal diverse spatial structures. The AGN hosts are compact, whereas the other galaxies show extended ionized gas on scales up to 10 kpc and star formation rates of 60 - 600 M_⊙yr^-1. One of the extended objects exhibits a signature of rotation, while most of the others show little ordered kinematics, with velocity widths (FWHM) up to 200 - 300 km s^-1. These objects populate the intermediate luminosity regime between classical luminous quasars and the low-luminosity AGNs discovered by JWST, including Little Red Dots, potentially linking the two populations.

@article{2026arXiv260610160M, author = {{Matsuoka}, Yoshiki and {Decarli}, Roberto and {Farina}, Emanuele Paolo and {Gloudemans}, Anniek J. and {Ba{\textasciitilde n}ados}, Eduardo and {Arrigoni Battaia}, Fabrizio and {Eilers}, Anna-Christina and {Mazzucchelli}, Chiara and {Strauss}, Michael A. and {Suh}, Hyewon and {Trebitsch}, Maxime and {Walter}, Fabian and {Wang}, Feige and {Aoki}, Kentaro and {Arita}, Junya}, title = {{Aether-SHELLQs: JWST integral-field spectroscopy of candidate obscured quasars at z \raisebox{-0.5ex}\textasciitilde 6}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.10160}, pages = {arXiv:2606.10160}, archiveprefix = {arXiv}, eprint = {2606.10160}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260610160M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, kinematics, spectroscopy}, month_numeric = {6} }

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Unveil the nature of JWST-AGN and Little Red Dots with SKAO continuum surveys

Giovanni Mazzolari, Dharam V. Lal, Isabella Prandoni, and 6 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

The advent of JWST has revealed a large population of AGN at z>4, which are \sim1 dex more abundant than previously expected, including also the enigmatic population of Little Red Dots (LRDs). Remarkably, the vast majority of JWST-discovered AGN and LRDs are not detected in X-rays, and most of them also show faint rest-frame UV continua and faint high-ionization emission lines, as well as unusually faint emission in the Mid and Far infrared. Recent studies investigating their radio properties have reported no significant detections, even in deep stacking analyses, reaching sensitivities of 0.5-0.1 μJy at z∼5-6, corresponding to L_R≲10^39\rm erg s^-1. While these non-detections may be consistent with a standard radio-quiet nature, some results suggest that the radio emission might instead be significantly suppressed by other physical phenomena. Three main scenarios have been proposed in the literature to explain the physical properties of these objects across the electromagnetic spectrum: Compton-thick absorption by a broad-line region with high covering-factor, intrinsically weak emission driven by high accretion rates, or the presence of a cocoon of dense ionized gas that produces strong scattering effects. The unprecedented sensitivity of SKAO will enable the detection of the radio emission of these AGN in all three cases. Because each scenario is expected to produce distinct radio signatures, future SKAO continuum surveys will be able to distinguish between them, uncovering the physical processes responsible for their peculiar properties. Observations spanning a wide range of integration times (1-1000 hours) and frequencies with SKA-Mid and SKA-Low (0.2-11 GHz) will allow us to characterize these objects from the local Universe to high redshift, investigate possible radio variability, and test alternative scenarios to black hole accretion.

@article{2026arXiv260630757M, author = {{Mazzolari}, Giovanni and {Lal}, Dharam V. and {Prandoni}, Isabella and {Gilli}, Roberto and {Maiolino}, Roberto and {{\"U}bler}, Hannah and {Delvecchio}, Ivan and {Brusa}, Marcella and {Mignoli}, Marco}, title = {{Unveil the nature of JWST-AGN and Little Red Dots with SKAO continuum surveys}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2026}, month = jun, eid = {arXiv:2606.30757}, pages = {arXiv:2606.30757}, archiveprefix = {arXiv}, eprint = {2606.30757}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260630757M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, multi-wavelength, radio, theory, variability}, month_numeric = {6} }

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Between Degeneracy and Evolution: UV-to-optical Insights into the BH^* Model in Little Red Dots

Rosa M. Mérida, Marcin Sawicki, Chris J. Willott, and 2 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Little Red Dots (LRDs) are a heterogeneous class of objects, with several proposed scenarios for their physical nature and evolution. While these theories have been tested on individual LRDs using limited spectral features, a systematic Bayesian analysis of the LRD population incorporating the different models across a broad wavelength range is still lacking. In this study, we conduct a consistent ultraviolet (UV)-to-optical continuum fitting analysis of 66 LRDs at 2<z<6 using JWST/NIRSpec PRISM spectroscopy. Employing a modified version of Bagpipes–including blackbody (BB) emission affected by Balmer absorption, stellar and nebular emission attenuated by dust, and an active galactic nucleus (AGN) component–we assess the performance of the black hole star (BH*) model in describing the LRD population. We adopt broad priors and therefore do not impose any specific physical scenario. Our results show that only \raisebox-0.5ex\textasciitilde6% of LRDs with statistically robust solutions (52 objects in total) are best- fit by a BH* in the optical and a host galaxy in the UV. \raisebox-0.5ex\textasciitilde8% of LRDs show BB-dominated optical continua but lack a stellar component or exhibit AGN UV leakage. Most LRDs are dominated by stellar and/or AGN emission in the optical, with minor BB contribution. When we adopt a prior that disfavors a strong AGN continuum to enforce BH*-like solutions, the percentage of BH^* systems increases to \raisebox-0.5ex\textasciitilde40%, highlighting the strong degeneracy between a BH* solution and alternative scenarios. Even when BH*-like solutions are enforced, many LRDs still require a stellar-dominated optical continuum. This may reveal limitations of the BH* model or point to an evolutionary sequence in which the BB contribution decreases as the host grows, leading to lower BB temperatures and higher stellar masses at lower z. In this scenario, more pronounced “V” shapes would correspond to later stages in LRD evolution.

@article{2026arXiv260612355M, author = {{M{\'e}rida}, Rosa M. and {Sawicki}, Marcin and {Willott}, Chris J. and {Gaspar}, Gaia and {Iyer}, Kartheik G.}, title = {{Between Degeneracy and Evolution: UV-to-optical Insights into the BH$^*$ Model in Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.12355}, pages = {arXiv:2606.12355}, archiveprefix = {arXiv}, eprint = {2606.12355}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260612355M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, jwst, sed, spectroscopy}, month_numeric = {6} }

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Little Red Dots as Intermediate Mass, Super-Eddington Engines: Insights from Type IIn Supernovae and The 1837-1856 Great Eruption of η Carinae

Rohan P. Naidu, Jorryt Matthee, Anna de Graaff, and 20 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

JWST’s Little Red Dots (LRDs) display a unique constellation of features that do not occur simultaneously in any other class of galaxies or AGN. Here we observe that many of these features find parallels in the 19th century Great Eruption (GE) of η Carinae and a sub-class of supernovae (Type IIn). Drawing on these stellar phenomena – outflows trapped by dense circumstellar gas envelopes – we sketch a possible scenario for LRDs. Outflows from the central engine produce an enshrouding envelope of gas that may be thought of as a slow wind. This dense wind and its enormous extent produce an opacity so high that a pseudo- photosphere forms within the wind, obscuring the central engine and manifesting as a blackbody-like continuum. Radiation from the buried engine powers the system. The engine may also launch fast winds that crash into the existing envelope to generate shocks. Lines form within the wind above the photosphere – electron scattering and absorption in the clumpy (ionized + neutral) medium account for broad wings and P-Cygni cores. A key implication is that inferences of “overmassive black holes” may be interpreting this wind-like physics as a virial broad- line region. We propose an escape velocity argument to constrain the mass of the engine, which yields M<10^5 M_⊙for the typical LRD. The lack of variability and low surface gravity of the photosphere provide further support for intermediate mass (M\approx10^3-6 M_⊙), but very luminous super-Eddington (L_\rmbol/L_\rmeddrsim5) systems harboring a supermassive star or intermediate mass black hole. Paralleling the evolution of IIn SNe, dust production in the envelope may mark the beginnings of classical AGN. This paper explores a possible self-consistent explanation for the entire life-cycle of LRDs, from their enshrouding in dense gas to their fates as seeds of massive black holes.

@article{2026arXiv260630711N, author = {{Naidu}, Rohan P. and {Matthee}, Jorryt and {de Graaff}, Anna and {Torralba}, Alberto and {Ashall}, Chris and {Katz}, Harley and {Chisholm}, John and {Brammer}, Gabriel and {Dessart}, Luc and {Eilers}, Anna-Christina and {Hviding}, Raphael E. and {Jones}, David O. and {Kokorev}, Vasily and {Leja}, Joel and {Liu}, Hanpu and {Liu}, Zhaoran and {Nandal}, Devesh and {Oesch}, Pascal A. and {Ransome}, Conor L. and {Simcoe}, Robert A. and {Sun}, Wendy Q. and {Weibel}, Andrea and {Xiao}, Mengyuan}, title = {{Little Red Dots as Intermediate Mass, Super-Eddington Engines: Insights from Type IIn Supernovae and The 1837-1856 Great Eruption of $η$ Carinae}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics}, year = {2026}, month = jun, eid = {arXiv:2606.30711}, pages = {arXiv:2606.30711}, archiveprefix = {arXiv}, eprint = {2606.30711}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260630711N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, exotic physics, heavy seed, super-eddington, theory}, month_numeric = {6} }

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The metallicities of little red dot host galaxies: LRDs are metal poor, but not pristine

G. P. Nikopoulos, D. Watson, C. L. Pollock, and 4 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Little Red Dots (LRDs) are a population of high-z sources discovered by JWST whose compactness, broad permitted lines, strong absorption features, continuum shapes and luminosities point to accreting supermassive black holes (SMBHs) embedded in dense gas. To date, the metallicity of the hosts of these systems has not been systematically measured. We determine the gas-phase metallicities of LRD host galaxies and test whether their narrow-line emission is consistent with metal poor star formation or AGN activity. We assemble a sample of 24 LRDs at z \raisebox-0.5ex~2.3-7 with medium and high- resolution JWST/NIRSpec data. We derive oxygen abundances and electron temperatures using the direct Te method applied exclusively to the narrow components of emission lines, and cross-check against widely used strong line calibrations. We derive a sample-averaged abundance of Z_T_\mathrme = 0.08_-0.03^+0.11\,\mathrmZ_⊙ (T_\mathrme = 23000_-7000^+17000 K), placing LRDs firmly in the metal-poor regime of high redshift star forming galaxies. The R-hat calibration yields a consistent average of Z_\hat\mathrmR = 0.07_-0.04^+0.07\,\mathrmZ_⊙, with only 4% scatter relative to the direct Te method, providing a robust proxy for systems where the [O III]4363Å line is not detected. We also identify two extremely metal-poor LRDs with metallicities <1.3%. The general population of LRDs are among the lower metallicity galaxies found by JWST at this epoch; they exhibit a narrow range of metallicities with a range of about 0.6 dex, which remains remarkably stable over cosmic time. Such low metallicity may then be a defining property of the class. The fact that LRDs have substantial metallicity across most of the class poses a challenge to models that require formation via pristine gas collapse, while their generally low metallicity indicates that they are not standard AGN.

@article{2026arXiv260631515N, author = {{Nikopoulos}, G. P. and {Watson}, D. and {Pollock}, C. L. and {Sneppen}, A. and {Heintz}, K. E. and {Witstok}, J. and {Brammer}, G.}, title = {{The metallicities of little red dot host galaxies: LRDs are metal poor, but not pristine}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.31515}, pages = {arXiv:2606.31515}, archiveprefix = {arXiv}, eprint = {2606.31515}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260631515N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, host galaxy, jwst, spectroscopy}, month_numeric = {6} }

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Evidence of violation of case B recombination in little red dots

G. P. Nikopoulos, D. Watson, A. Sneppen, and 4 more authors

Astronomy & Astrophysics, Jun 2026

Abs DOI ADS arXiv

Context. Little Red Dots (LRDs) are a new class of compact extragalactic objects with a v-shaped optical spectral energy distribution breaking close to the Balmer break wavelength and broad, typically exponentially shaped lines. They are believed to be supermassive black holes surrounded by very dense ionised gas, leading us to search for any departures from case B recombination in these systems. Aims. For this paper we examined the ratios of multiple hydrogen Balmer lines (H\ensuremathα, H\ensuremathβ, H\ensuremathγ, and H\ensuremathδ) to determine whether there is indication of deviation from simple case B recombination processes. Methods. We analysed a dozen high-S/N LRDs with JWST/NIRSpec and measured Balmer ratios in the seven objects with coverage of at least three lines. We decomposed the line ratios into their respective broad and narrow components. Results. Broad-line ratios are consistent with case B plus severe dust extinction in all objects but one, RUBIES- EGS-4233_49140 at z = 6.68; in this case the ratios deviate by more than 5\ensuremathσ and are inconsistent with all known dust curves. The narrow components are consistent with minimal dust attenuation, while two objects exhibit narrow H\ensuremathα/H\ensuremathβ ≍ 1.8. Conclusions. Such low decrements are observed in highly ionised density bounded nebulae, associated with starburst environments. Nevertheless, the two flat decrement cases can be reconciled assuming an unresolved absorption feature. RUBIES EGS-49140 shows a high broad H\ensuremathα/H\ensuremathβ, but the H\ensuremathγ/H\ensuremathα and H\ensuremathδ/H\ensuremathα ratios are lower than expected for extinction-modified case B, hinting at an unphysically steep dust law. These line ratios may be due to increased optical depth in the Balmer lines as a direct effect of high-density gas (log n_e > 9) surrounding the black hole. If case B recombination does hold in most LRDs, they must be moderately to heavily dust obscured (A_V ≃ 1\ensuremath-8), while the host-galaxy should be dust-free, suggesting that the extinction in the broad lines is local to the LRD and is not due to the general interstellar medium of the host galaxy. Nevertheless, this dust-based scenario poses several caveats. The apparent general consistency of LRDs with case B may be an artefact of H\ensuremathγ and H\ensuremathδ non-detections.

@article{2026A&A...710A.136N, author = {{Nikopoulos}, G. P. and {Watson}, D. and {Sneppen}, A. and {Rusakov}, V. and {Heintz}, K. E. and {Witstok}, J. and {Brammer}, G.}, title = {{Evidence of violation of case B recombination in little red dots}}, journal = {\aap}, keywords = {dust, extinction, galaxies: active, galaxies: evolution, galaxies: high-redshift, galaxies: nuclei}, year = {2026}, month = jun, volume = {710}, eid = {A136}, pages = {A136}, doi = {10.1051/0004-6361/202557604}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...710A.136N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2510.06362}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {agn-dominated, emission lines, jwst, obscuration, spectroscopy}, month_numeric = {6} }

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The Structure and Evolution of LRDs: Insights from JWST NIRSpec Medium- and High-resolution Spectroscopy at z \ensuremath∼ 4

Yuxuan Pang, Xin Wang, Cheng Cheng, and 5 more authors

The Astrophysical Journal, Jun 2026

Abs DOI ADS arXiv

We present an analysis of medium-/high-resolution JWST/NIRSpec spectra for 11 Little Red Dots (LRDs) at z \ensuremath∼ 4. By decomposing the broad and narrow components of the Balmer emission lines, we investigate the connection between line emission and UV/optical continua for the LRD population. We find that the broad H\ensuremathα luminosity strongly correlates with the optical continuum (but not with the UV), indicating a common active galactic nucleus (AGN) origin for both. In contrast, the [O III] line strength is correlated with the UV continuum rather than the optical. Using the width and luminosity of the broad H\ensuremathα line, we estimate central black hole masses of 10^6─10^8M_\ensuremath⊙ accreting at high Eddington ratios (\ensuremathλ_Edd \ensuremath∼ 0.6), consistent with an early, rapid-growth phase of AGN evolution. Assuming a constant mass accretion rate in the framework of slim-disk models, we infer growth timescales of \ensuremath∼10^5─10^7 yr, and suggest LRDs may evolve into narrow-line Seyfert 1 galaxies. Upper limits from our spectra indicate that LRDs exhibit intrinsically weak optical Fe II emission compared to typical AGN. To simultaneously account for the inferred broad-line region size and observed luminosity, we propose a “clumpy envelope” model in which the optical emission arises from an extended, clumpy gas with a characteristic radius of tens of light-days. The diversity in observed optical continuum shapes can be explained by radial temperature gradients and self-absorption effects within this structure. Our results demonstrate the power of JWST high-resolution spectroscopy in probing the central engines and physical nature of the LRD population.

@article{2026ApJ..1004..185P, author = {{Pang}, Yuxuan and {Wang}, Xin and {Cheng}, Cheng and {Wang}, Shengzhe and {Zhou}, Hang and {Zhou}, Qianqiao and {Wu}, Xue-Bing and {Glazebrook}, Karl}, title = {{The Structure and Evolution of LRDs: Insights from JWST NIRSpec Medium- and High-resolution Spectroscopy at z {\ensuremath{\sim}} 4}}, journal = {\apj}, keywords = {Active galactic nuclei, Supermassive black holes, Galaxy evolution, James Webb Space Telescope, 16, 1663, 594, 2291}, year = {2026}, month = jun, volume = {1004}, number = {2}, eid = {185}, pages = {185}, doi = {10.3847/1538-4357/ae6e3f}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1004..185P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2602.12548}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {agn-dominated, black hole mass, emission lines, jwst, spectroscopy}, month_numeric = {6} }

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NEXUS: Abundance, Environments, and Spectral Diversity of Little Red Dots from the NIRSpec MSA Sample

Zhiwei Pan, Ming-Yang Zhuang, Yue Shen, and 6 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

We present a comprehensive study of Little Red Dots (LRDs) at 2.3 90%) of the spectroscopically confirmed LRDs have robust broad-line detection. Our spectroscopic sample of 36 LRDs displays the full range of spectral diversity of LRDs. It includes objects with extreme Balmer breaks similar to the LRD “Cliff”, as well as objects with moderately reddened rest-optical continua that can be fit with low-temperature blackbody components in the recent BH* model framework. The broad Hα emission is correlated with the continuum emission at 5100 Angstrom, suggesting common origins for these emission components; the narrow [O III] emission, however, is poorly correlated with the optical continuum. We do not find evidence of redshift evolution in these spectral properties. The space density of LRDs declines toward z about 2, opposite to the trend for normal AGNs, although low-luminosity LRDs at z about 2-4 may be more abundant than currently probed by ground-based searches. The clustering of LRDs suggests that they live in dark matter halos of several times 10^11 h^-1 solar masses, albeit with large uncertainties. Overall, these results are consistent with recent observations of LRDs and with the emerging picture of accreting SMBHs enshrouded in dense gas envelopes as the origin of LRDs.

@article{2026arXiv260609721P, author = {{Pan}, Zhiwei and {Zhuang}, Ming-Yang and {Shen}, Yue and {Wang}, Feige and {Greene}, Jenny E. and {Burgasser}, Adam J. and {Li}, Junyao and {Stone}, Zachary and {Venkatraman}, Padmavathi}, title = {{NEXUS: Abundance, Environments, and Spectral Diversity of Little Red Dots from the NIRSpec MSA Sample}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.09721}, pages = {arXiv:2606.09721}, archiveprefix = {arXiv}, eprint = {2606.09721}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260609721P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, clustering, jwst, sample selection, spectroscopy}, month_numeric = {6} }

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SEEDZ: Rapid Galaxy Assembly as a Pathway to Supermassive Stars, Dense Stellar Environments and Massive Black Hole Seeds

Lewis R. Prole, John A. Regan, Daxal Mehta, and 14 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

We investigate the assembly history of early galaxies in the SEEDZ hydrodynamic simulations, to investigate the high inflow rates believed to be required for the formation of supermassive stars (SMSs), dense stellar clusters and subsequently heavy seed black holes. Using a heavy seed formation criteria of >1 M_⊙yr^-1 flowing into 10 pc regions, we find that heavy seeds form in halos that grow rapidly compared to those halos that never meet the criteria. Halos with growth rates of rsim1 M_⊙yr^-1 at their virial radius (scales of a few hundred pc) are able to sustain a flow rate of 0.1 M_⊙yr^-1 into the inner 1 pc of the halo, maintaining higher density environments within the central 10 - 100\raisebox-0.5ex\textasciitildepc. These halos continue to grow rapidly after their initial collapse, typically forming heavy seeds \sim100 Myr after forming their first stars and stellar mass black holes. By z=10, most heavy seeds form in regions of near-solar metallicity, although a minority of heavy seeds do continue to form in low metallicity (10^-2 Z_⊙) regions. Under the assumption that a SMS forms as the progenitor to a heavy seed if it forms in a region of low (10^-2 Z_⊙) metallicity, and can sustain high accretion rates above 0.02 M_⊙yr^-1 throughout the SMS lifetime of 2 Myr, we find a number density of SMSs of 0.1 cMpc^-3, meaning that only a fraction of 10^-4 of these SMSs would need to be visible to JWST to account for the observed population of Little Red Dot galaxies.

@article{2026arXiv260627427P, author = {{Prole}, Lewis R. and {Regan}, John A. and {Mehta}, Daxal and {Nandal}, Devesh and {Pakmor}, R{\"u}diger and {Beckmann}, Ricarda S. and {Tremmel}, Michael and {Haehnelt}, Martin G. and {Glover}, Simon C. O. and {Klessen}, Ralf S. and {Wise}, John H. and {Koudmani}, Sophie and {Bourne}, Martin A. and {Sijacki}, Debora and {Brennan}, John and {van de Bor}, Pelle and {Clark}, Paul C.}, title = {{SEEDZ: Rapid Galaxy Assembly as a Pathway to Supermassive Stars, Dense Stellar Environments and Massive Black Hole Seeds}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, Solar and Stellar Astrophysics}, year = {2026}, month = jun, eid = {arXiv:2606.27427}, pages = {arXiv:2606.27427}, archiveprefix = {arXiv}, eprint = {2606.27427}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260627427P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, early universe, exotic physics, heavy seed, simulation}, month_numeric = {6} }

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The Stellar Origin of “V-shaped” Spectral Energy Distributions in Ly\ensuremathα-emitting Little Red Dots Revealed by JWST/MIRI

Jian Ren, F. S. Liu, Nan Li, and 8 more authors

The Astrophysical Journal, Jun 2026

Abs DOI ADS

Understanding the nature of the high-redshift “V-shaped” little red dots (LRDs) recently uncovered by the James Webb Space Telescope (JWST) is crucial for constraining the early coevolution of galaxies and supermassive black holes (SMBHs). Leveraging deep JWST multiband imaging in the GOODS-S field, we photometrically identify six LRDs from a parent sample of MUSE-selected Ly\ensuremathα emitters (LAEs). Their Ly\ensuremathα line profiles are asymmetric, with suppressed blue wings and narrow widths (FWHM 1 \ensuremathμm), an active galactic nucleus (AGN) could contribute \ensuremath∼40% of the rest-frame optical luminosity. However, when MIRI data are included, the long-wavelength emission is well reproduced by stellar populations with strong nebular emission in four sources, independent of the inclusion of an AGN component. Morphological analysis reveals that these systems are compact in the rest-frame optical, while exhibiting more extended structures in the rest-frame UV. These results suggest that AGN activity is not required to explain the observed properties of most narrow-line LRDs in our sample. Instead, they are consistent with being compact, star-forming galaxies, although contributions from low-luminosity or obscured AGN cannot be entirely ruled out. Thus, rest-frame near-infrared observations are essential to interpret LRDs, and infrared excesses alone do not reliably indicate AGN activity.

@article{2026ApJ..1003..150R, author = {{Ren}, Jian and {Liu}, F. S. and {Li}, Nan and {Song}, Qi and {Zhao}, Pinsong and {Cui}, Qifan and {Li}, Yubin and {Mo}, Hao and {Wang}, Guanghuan and {Yesuf}, Hassen M. and {Wang}, Weichen}, title = {{The Stellar Origin of ``V-shaped'' Spectral Energy Distributions in Ly{\ensuremath{\alpha}}-emitting Little Red Dots Revealed by JWST/MIRI}}, journal = {\apj}, keywords = {Lyman-alpha galaxies, AGN host galaxies, Galaxy evolution, High-redshift galaxies, 978, 2017, 594, 734}, year = {2026}, month = jun, volume = {1003}, number = {2}, eid = {150}, pages = {150}, doi = {10.3847/1538-4357/ae5e4d}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1003..150R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, morphology, non-agn, sed, starburst}, month_numeric = {6} }

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MEGA: Spectrophotometric Spectral Energy Distribution Fitting of Little Red Dots Detected in JWST MIRI

Kaila Ronayne, Casey Papovich, Allison Kirkpatrick, and 13 more authors

The Astrophysical Journal, Jun 2026

Abs DOI ADS arXiv

We analyze eight spectroscopically confirmed little red dots (LRDs) at redshifts z = 5.1─8.7 with JWST/NIRCam, NIRSpec, and MIRI data. The LRDs have red NIRCam colors, F150W \ensuremath- F444W > 1, but flat NIRCam \ensuremath- MIRI colors, \ensuremath-0.5 < F444W \ensuremath- F770W < 0.5, suggesting weak warm/hot dust components. The LRDs have \ensuremath-1.0 < F1000W \ensuremath- F1500W < 1.1, suggestive of nonuniform rest near-IR properties within the sample. We model the spectral energy distributions (SEDs) of the LRDs using the CIGALE and PROSPECTOR codes to assess how the differing templates impact the interpretation for LRDs for cases of: (1) models with star-forming (SF) stellar populations only; (2) active galactic nuclei (AGN)-dominated models; and (3) composite AGN and SF models. Using the Bayesian information criterion, we find that six of the eight LRDs favor AGN models compared to SF models, though no model reproduces all of the observed properties. Two LRDs with pronounced Balmer breaks and broad H\ensuremathα have SEDs that are reproduced with hot, dense-gas (logT/K=5─5.7, logn/cm\ensuremath-3=9─11) models with low dust attenuation (A(V) ≃ 0.5 mag). However, these models require an additional thermal component (800─1400 K) to account for the MIRI data, and fail to reproduce the rest- UV and narrow [O III] emission. The total bolometric emission from the dense-gas models, and possibly CIGALE AGN models, appears consistent with literature constraints in the far-IR and radio, and requires logLbol/L\ensuremath⊙12. These results suggest that our LRDs cannot be modeled entirely with standard templates, but instead require a novel treatment of gas conditions, AGN, and star formation.

@article{2026ApJ..1003..234R, author = {{Ronayne}, Kaila and {Papovich}, Casey and {Kirkpatrick}, Allison and {Backhaus}, Bren E. and {Cullen}, Fergus and {Shen}, Lu and {Bagley}, Micaela B. and {Barro}, Guillermo and {Finkelstein}, Steven L. and {Hamblin}, Kurt and {Kartaltepe}, Jeyhan S. and {Kocevski}, Dale D. and {Koekemoer}, Anton M. and {Lambrides}, Erini and {Pacucci}, Fabio and {Yang}, Guang}, title = {{MEGA: Spectrophotometric Spectral Energy Distribution Fitting of Little Red Dots Detected in JWST MIRI}}, journal = {\apj}, keywords = {James Webb Space Telescope, Active galactic nuclei, Star formation, 2291, 16, 1569, Astrophysics of Galaxies}, year = {2026}, month = jun, volume = {1003}, number = {2}, eid = {234}, pages = {234}, doi = {10.3847/1538-4357/ae5e6b}, archiveprefix = {arXiv}, eprint = {2508.20177}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1003..234R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, composite, early universe, jwst, sed}, month_numeric = {6} }

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Little Red Dots on FIRE: Exploring the formation and observational signatures of ultra-compact early galaxies

Niranjan Chandra Roy, Daniel Anglés-Alcázar, Rachel K. Cochrane, and 15 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Little Red Dots (LRDs) are compact sources with broad Balmer lines, Balmer breaks, anomalous UV emission, rising red continuum, and uncertain origin. We use FIRE cosmological simulations, 3D dust radiative transfer, and synthetic emission-line data cubes to test whether ultra-compact early galaxies can reproduce LRD-like observables without invoking AGN. In progenitors of present-day group halos (M_\rm halo > 10^13.5 M_⊙), we identify transient phases at z ≈4-8 lasting ∼150-400 Myr in which strong dissipative inflows build massive (M_⋆ ∼10^8.5-10^10.5 M_⊙), UV-bright (-23 ≲M_\rm UV ≲-20), ultra-compact (R_\rm eff 500 km s^-1) and consistent with several LRD properties: strong Balmer breaks (F_ν(4200\rm Å)/F_ν(3500\rm Å) ∼2); blue UV beta slopes (β_\rm UV ≈-1.25); dust masses; ALMA non-detections; and Balmer-line widths up to ∼1500 km s^-1 broadened by galaxy-scale dynamics. However, stellar emission and host-galaxy kinematics alone do not reproduce the red rest-optical continuum, more extreme Balmer breaks (rsim 2.5) and line widths (rsim 2000 km s^-1), or the broad-Balmer/narrow-forbidden-line signature of broad- line AGN. The same ultra-compact conditions efficiently fuel central BHs, suggesting a hybrid stellar+AGN scenario in which compact stars explain the UV continuum, Balmer break, and intermediate line widths while AGN supply the red optical continuum and more extreme line properties. With halo masses M_\rm halo ∼10^11-12.5 M_⊙and comoving abundance ∼2 \times 10^-5 \rm cMpc^-3 (for ∼20% duty- cycle at z ≈4-8), ultra-compact galaxies can contribute to the massive, bright LRD population.

@article{2026arXiv260623683R, author = {{Roy}, Niranjan Chandra and {Angl{\'e}s-Alc{\'a}zar}, Daniel and {Cochrane}, Rachel K. and {Richings}, Alexander J. and {Mercedes-Feliz}, Jonathan and {Hayward}, Christopher C. and {Faucher-Gigu{\`e}re}, Claude-Andr{\'e} and {Lambrides}, Erini and {Feldmann}, Robert and {Oh}, Boon Kiat and {Marszewski}, Andrew and {Sun}, Guochao and {Davis}, Kelcey and {McKinney}, Jed and {Casey}, Caitlin M. and {D{\'\i}az-Santos}, Tanio and {Brooks}, Madisyn and {Farrell}, Grace}, title = {{Little Red Dots on FIRE: Exploring the formation and observational signatures of ultra-compact early galaxies}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.23683}, pages = {arXiv:2606.23683}, archiveprefix = {arXiv}, eprint = {2606.23683}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260623683R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, early universe, kinematics, morphology, simulation}, month_numeric = {6} }

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The Extreme Rarity and Physical Properties of Low-redshift AGNs with Balmer Absorption

Jinyi Shangguan, Chang-Hao Chen, Luis C. Ho, and 6 more authors

arXiv e-prints, Jun 2026

Abs DOI ADS arXiv

Balmer absorption lines are increasingly observed in the little red dots (LRDs) discovered by the James Webb Space Telescope, potentially tracing dense circumnuclear gas around rapidly accreting black holes. Motivated by this connection, we search for Balmer absorption using homogeneously analyzed spectra of a representative parent sample of 14,584 low-redshift (z<0.35) type 1 active galactic nuclei selected from the Sloan Digital Sky Survey. We identify seven sources with robust Balmer absorption (occurrence ∼0.05%) and model them with a partially covering absorber model, accounting for the spectral resolution. By fitting Hα, Hβ, and Hγ simultaneously and tying their optical-depth ratios to theoretical values, we constrain optical depth at the line center (τ_0) and the covering factor (C_f). All sources with robust modeling require optically thick Hα absorption and typically moderate covering factors (C_f≈0.2-0.6), while the LRD analog J1025 shows C_f rsim 0.8 consistent with recent measurements of high-redshift LRDs. The absorbers have modest velocity offsets (∼150-850\,\mathrmkm s^-1) and narrow intrinsic widths (∼20-200\,\mathrmkm s^-1). Multi- epoch spectroscopy of three sources reveals Balmer-absorption variability on both year and month timescales. Three objects exhibit exceptionally weak Fe II emission, high Eddington ratio, and low gas-phase metallicity, an atypically rare combination of properties that might elevate the incidence of Balmer-absorption to \sim10%. We argue that low-metallicity conditions may suppress disk winds and help retain dense neutral gas along the line-of-sight in systems of high accretion rate.

@article{2026arXiv260604712S, author = {{Shangguan}, Jinyi and {Chen}, Chang-Hao and {Ho}, Luis C. and {Liao}, Jiwei and {Liu}, Yanqing and {Wu}, Chengzhou and {Li}, Ruancun and {Inayoshi}, Kohei and {Jiang}, Linhua}, title = {{The Extreme Rarity and Physical Properties of Low-redshift AGNs with Balmer Absorption}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = jun, eid = {arXiv:2606.04712}, pages = {arXiv:2606.04712}, doi = {10.48550/arXiv.2606.04712}, archiveprefix = {arXiv}, eprint = {2606.04712}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260604712S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, local counterpart, spectroscopy, variability}, month_numeric = {6} }

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TBD LBD: The nature of ‘little blue dots’

Albert Sneppen, Darach Watson, James H. Matthews, and 1 more author

arXiv e-prints, Jun 2026

Abs ADS arXiv

Previous Sirocco radiative-transfer models of gas-cocooned AGN predicted lower-column counterparts to little red dots (LRDs): compact, X-ray-weak sources with bluer continuum slopes and Balmer jumps rather than Balmer breaks. The recently identified population of little blue dots (LBDs) closely resembles this predicted phase. Here we explore these lower-column-density cocoons in which nebular recombination emission remains visible while strong Balmer-continuum absorption is avoided. We find that a sequence of increasing column density connects more classical AGN spectra, Balmer-jump LBD-like spectra at N_\rm H\!∼\!\rm few\times10^24 \mathrmcm^-2, and Balmer-break LRD-like spectra at higher columns. In this sequence, electron scattering produces exponential line wings and suppresses X-ray emission before strong Balmer absorption features, characteristic of higher column densities, appear. We therefore propose that LBDs are lower-column analogues of LRDs within a common gas-cocooned AGN sequence. This interpretation predicts that Balmer-jump emission, X-ray weakness, permitted lines with exponential wings, He II λ4686 emission, smaller Hα FWHM values and equivalent widths than in LRDs, and weak or absent absorption features are characteristic of LBDs. We compare to three example LBD spectra and identify Balmer-jump signatures in them.

@article{2026arXiv260612509S, author = {{Sneppen}, Albert and {Watson}, Darach and {Matthews}, James H. and {Nikopoulos}, Georgios}, title = {{TBD LBD: The nature of `little blue dots'}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = jun, eid = {arXiv:2606.12509}, pages = {arXiv:2606.12509}, archiveprefix = {arXiv}, eprint = {2606.12509}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260612509S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, obscuration, simulation, theory}, month_numeric = {6} }

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Constraints on the Gas Geometry Surrounding Little Red Dots through Narrow-Line Diagnostics

Visal Sok, Erica J. Nelson, Mitchell C. Begelman, and 10 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Little Red Dots (LRDs) are a recently identified population of high- redshift sources, with a common interpretation being accreting black holes embedded within a spherical, optically thick gas envelope. Within this framework, some models propose that the continuum arises from the dense-gas envelope, where hard ionizing radiation from the central engine is reprocessed into a stellar-like photosphere with an effective temperature of \sim5000 K. This implies that both the UV continuum and narrow-line emission are then powered by the host galaxy rather than an exposed central engine. To test whether this is consistent with the observed narrow-line ratios, we analyze multiple line diagnostics for a sample of \sim20 LRDs with high signal-to-noise NIRSpec grating spectra. We find that at least 40\% of the LRDs have line ratios pointing toward high ionization parameter and electron temperature, with a further 15\% also falling in the AGN regime for the O\textbackslashtextsc{i}/Hα diagnostic, indicative of harder ionizing radiation. These line ratios are incompatible with stellar photoionization from a star-forming host alone. This suggests lower density channels within the gas envelope through which high energy photons can escape and excite the surrounding narrow-line emitting gas. At the same time, most LRDs lack strong high-ionization line emission, with He\,\textbackslashtextsc{ii}/Hβ \lesssim0.1, consistent with an ionizing spectrum softer than that of a standard AGN. Together, these results disfavour a uniform gas envelope with a covering fraction of unity, and instead point to a more complex geometry that gives rise to anisotropic ionizing radiation.

@article{2026arXiv260623778S, author = {{Sok}, Visal and {Nelson}, Erica J. and {Begelman}, Mitchell C. and {Dexter}, Jason and {D'Eugenio}, Francesco and {Greene}, Jenny E. and {Leja}, Joel and {Whitaker}, Katherine E. and {Bunker}, Andrew J. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Rinaldi}, Pierluigi and {Torralba}, Alberto and {{\"U}bler}, Hannah}, title = {{Constraints on the Gas Geometry Surrounding Little Red Dots through Narrow-Line Diagnostics}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.23778}, pages = {arXiv:2606.23778}, archiveprefix = {arXiv}, eprint = {2606.23778}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260623778S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, emission lines, jwst, obscuration, spectroscopy}, month_numeric = {6} }

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Mass and Spin Growth of Very Massive Stars in Star Clusters Potentially Associated with Little Red Dots

Ataru Tanikawa, Masaru Shibata, and Kunihito Ioka

arXiv e-prints, Jun 2026

Abs DOI ADS arXiv

Using gravitational N-body simulations, we investigate the evolution of mass and spin for very massive stars (VMSs) in dense star clusters, which may be potentially associated with Little Red Dots (LRDs). Our results show that VMS masses can reach 10^3–10^4 M_⊙, depending on the initial conditions of the host clusters. Notably, the VMS mass increases by up to a factor of three when accounting for the bloated state at the Hayashi track induced by stellar collisions, provided that this state is maintained at accretion rates exceeding 3 \times 10^-2 M_⊙\,\rm yr^-1. In all cases, the spin of the VMS, when normalized to the dimensionless black hole (BH) spin parameter, exceeds 10. While our model may overestimate VMS masses and spins due to the omission of post-main-sequence evolution and the loss of mass and angular momentum during collisions, we nonetheless demonstrate that VMSs formed in dense star clusters can be highly spinning. Such a rapidly spinning VMS is expected to collapse into an intermediate-mass BH surrounded by a massive accretion disk. This BH-disk system could trigger powerful explosions and emit burst gravitational waves, similar to those observed in GW190521 and GW231123, for which the remnant BH masses are estimated to be rsim 100 M_⊙.

@article{2026arXiv260601870T, author = {{Tanikawa}, Ataru and {Shibata}, Masaru and {Ioka}, Kunihito}, title = {{Mass and Spin Growth of Very Massive Stars in Star Clusters Potentially Associated with Little Red Dots}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, Solar and Stellar Astrophysics}, year = {2026}, month = jun, eid = {arXiv:2606.01870}, pages = {arXiv:2606.01870}, doi = {10.48550/arXiv.2606.01870}, archiveprefix = {arXiv}, eprint = {2606.01870}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260601870T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {exotic physics, heavy seed, simulation, starburst, theory}, month_numeric = {6} }

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Black Hole Stars Across the Universe: Identifying Central Engine Dominated Little Red Dots at z\sim1.5-9.5

Andrea Weibel, Rohan P. Naidu, Pascal A. Oesch, and 16 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

Photometric selections of Little Red Dots (LRDs) largely rely on identifying their “V-shaped” spectral energy distribution (SED). Recent work suggests this V-shape stems from a combination of a central engine – also referred to as a Black Hole Star (BH*) – and a star-forming host galaxy. We present a new and highly complementary photometric selection that is based on incorporating BH* templates in the \textbackslashtexttt{eazy} redshift fitting code. Selecting compact sources where a BH* template contributes >80\% to the best fitting SED in the rest- optical, we compile a sample of 241 BH*-dominated candidates from \sim1000\,\rm arcmin^2 of legacy and pure parallel JWST imaging. Our selection does not require a blue UV-component, and it successfully identifies objects that resemble the paradigmatic sources “MoM-BH*-1“ and “The Cliff”. We find that BH*-dominated sources exist across a wide range of redshifts (z\sim1.7-9.3) and optical luminosities (log(L_5100/\rm erg\,\rm s^-1)\sim42-44.5), and we measure a median Balmer break strength of \sim3, with some breaks reaching values >10. We estimate bolometric luminosities in the range log(L_\rm bol/\rm erg\,\rm s^-1)\sim42-45, which, assuming accretion at the Eddington- limit, would translate to black hole masses of M_\rm BH\sim10^4-10^7\rm M_⊙, spanning the intermediate mass black hole to the quasar regime. The number density of BH*-dominated candidates peaks at z\sim5-6 (\sim10^-5\,\rm Mpc^-3) and it declines by an order of magnitude down to z\sim2. Tentatively, comparing to V-shaped LRD samples suggests that the fraction of BH*-dominated sources among the broader LRD population does not decrease towards lower redshift. Crucially, our work demonstrates that BH*-dominated sources are not merely an early-Universe phenomenon but rather persist at least until cosmic noon.

@article{2026arXiv260617271W, author = {{Weibel}, Andrea and {Naidu}, Rohan P. and {Oesch}, Pascal A. and {de Graaff}, Anna and {Hviding}, Raphael E. and {Liu}, Zhaoran and {Matthee}, Jorryt and {Williams}, Christina C. and {Brammer}, Gabriel and {Covelo Paz}, Alba and {Greene}, Jenny E. and {Jespersen}, Christian Kragh and {Ji}, Zhiyuan and {Maseda}, Michael V. and {Setton}, David J. and {Sun}, Wendy Q. and {Torralba}, Alberto and {Witten}, Callum and {Xiao}, Mengyuan}, title = {{Black Hole Stars Across the Universe: Identifying Central Engine Dominated Little Red Dots at $z\sim1.5-9.5$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.17271}, pages = {arXiv:2606.17271}, archiveprefix = {arXiv}, eprint = {2606.17271}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260617271W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, catalog, jwst, sample selection, sed}, month_numeric = {6} }

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A Population of Red Galaxies with Very Strong Emission Lines at z > 5 Revealed by the NIRCam Medium Bands: “Classic” LRDs, Dusty Star-Forming Galaxies, and a Missing Population of LRDs

Sunna Withers, Adam Muzzin, Swara Ravindranath, and 16 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

The NIRCam medium-bands have proven to be efficient at identifying Emission Line Galaxies (ELGs) with high equivalent width (EW) Hα and [OIII]+Hβ emission lines. In this paper we exploit this efficiency to identify a sample of ELGs at 4.9 ≲z ≲8.9 using medium-band imaging from the CANUCS, Technicolor, and JUMPS surveys. We find that the ELGs exhibit a strong correlation between continuum color and emission line strength, such that galaxies with bluer UV/optical continua have stronger Hα and [OIII]+Hβ emission lines. We identify 26 galaxies that are outliers from this relation, which we call the Red Emission line Galaxies (REGs), because of their red continuum color and strong emission lines. We classify the REGs into three categories: 1) “classic” Little Red Dots (LRDs) selected with common literature criteria, 2) extended REGs, resolved in F444W and consistent with being Dusty Star Forming Galaxies (DSFGs), and 3) compact REGs, unresolved in F444W but not classified as LRDs. The compact REGs fail common LRD selections for several reasons, including faint continuua, contamination from emission lines (very strong [OIII]+Hβ), and UV/optical colors that are flatter than those of LRDs. We conclude that the compact REGs are likely LRDs that “classic” selection criteria miss, and are therefore missing from existing samples. Our results suggest that medium-band selection can provide more complete samples of these objects.

@article{2026arXiv260606585W, author = {{Withers}, Sunna and {Muzzin}, Adam and {Ravindranath}, Swara and {Willott}, Chris J. and {Martis}, Nicholas S. and {Tripodi}, Roberta and {Asada}, Yoshihisa and {Brada{\v{c}}}, Maru{\v{s}}a and {Merchant}, Maya and {Mowla}, Lamiya and {Noirot}, Ga{\"e}l and {Sarrouh}, Ghassan T. E. and {Sawicki}, Marcin and {Antwi-Danso}, Jacqueline and {Harshan}, Anishya and {Jagga}, Naadiyah and {Marchesini}, Danilo and {Myers}, Katherine and {Sok}, Visal}, title = {{A Population of Red Galaxies with Very Strong Emission Lines at $z > 5$ Revealed by the NIRCam Medium Bands: ``Classic'' LRDs, Dusty Star-Forming Galaxies, and a Missing Population of LRDs}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.06585}, pages = {arXiv:2606.06585}, archiveprefix = {arXiv}, eprint = {2606.06585}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260606585W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, morphology, sample selection}, month_numeric = {6} }

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A Scaling Relation of LRDs between Broad Hα and Bolometric Luminosities: Enhanced Broad Hα Emission Relative to Low-z Type 1 AGN

Hiroto Yanagisawa, Masami Ouchi, Tomokazu Kiyota, and 6 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

We investigate the demography of little red dots (LRDs) using 37 objects at z\sim3-7 with JWST/NIRSpec PRISM and grating spectra compiled from various JWST programs. We focus on spectroscopic quantities of the broad Hα luminosity L_\mathrmHα,broad (and the broad Hβ luminosity L_\mathrmHβ,broad where available) and the bolometric luminosity L_\mathrmbol represented by modified blackbody emission, avoiding quantities contaminated by host-galaxy emission (e.g., total Hα luminosity). We identifiy a tight scaling relation between L_\mathrmHα,broad and L_\mathrmbol, supporting the interpretation that these emissions are primarily powered by the central engine. Interestingly, the L_\mathrmHα,broad-L_\mathrmbol scaling relation of LRDs is enhanced by a factor of \sim40 in L_\mathrmHα,broad relative to that of low-z Type 1 AGN. A similar trend is found in the L_\mathrmHβ,broad-L_\mathrmbol relation, although the enhancement in L_\mathrmHβ,broad is smaller, only by a factor of \sim10. We explore the physical origin of these enhancements and find that \textbackslashtextsc{Cloudy} photoionization modeling within the classic locally optimally- emitting cloud (LOC) framework can explain them through an increase in the covering factor from \sim20\% (Type 1 AGN) to \sim100\% (LRDs), together with an increase in the hydrogen column density from N_\mathrmH\sim10^23\,\mathrmcm^-2 to rsim10^24\,\mathrmcm^-2, with a preferred gas density of \sim10^10\,\mathrmcm^-3, successfully reproducing the modified blackbody emission. Such a nearly unity covering factor without requiring a gas density increase may result from a significant increase in the BLR filling factor or size, corresponding to a “stuffed BLR“ or “giant BLR,” respectively.

@article{2026arXiv260609726Y, author = {{Yanagisawa}, Hiroto and {Ouchi}, Masami and {Kiyota}, Tomokazu and {Kageura}, Yuta and {Ando}, Makoto and {Harikane}, Yuichi and {Nakane}, Minami and {Ono}, Yoshiaki and {Takeda}, Yui}, title = {{A Scaling Relation of LRDs between Broad H$α$ and Bolometric Luminosities: Enhanced Broad H$α$ Emission Relative to Low-$z$ Type 1 AGN}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = jun, eid = {arXiv:2606.09726}, pages = {arXiv:2606.09726}, archiveprefix = {arXiv}, eprint = {2606.09726}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260609726Y}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, emission lines, jwst, obscuration, spectroscopy}, month_numeric = {6} }

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Smoluchowski Coagulation equation and the Evolution of Primordial Black Hole Clusters

Borui Zhang, Wei-Xiang Feng, and Haipeng An

\jcap, Jun 2026

Abs DOI ADS arXiv

In ref. arXiv:2507.07171, we demonstrate that the high-redshift supermassive black holes in the so-called “little red dots” discovered by James Webb Space Telescope (JWST) can be explained by the primordial black hole (PBH) clustering on small scales. In this paper, we present a comprehensive simulation of the successive PBH mergers within a cluster by solving the Smoluchowski coagulation equation. We derive the coagulation kernel considering both cases with and without the effects of mass segregation. Then we employ the Monte Carlo method to solve the equation, implementing the full-conditioning scheme using the discrete inverse transformation method. Our simulations determine the runaway timescales of clusters and the mass population evolution of PBHs across a wide range of cosmic redshifts, depending on the number of PBHs within the cluster and the associated density.

@article{2026JCAP...06..097Z, author = {{Zhang}, Borui and {Feng}, Wei-Xiang and {An}, Haipeng}, title = {{Smoluchowski Coagulation equation and the Evolution of Primordial Black Hole Clusters}}, journal = {\jcap}, keywords = {active galactic nuclei, massive black holes, primordial black holes, Statistical sampling techniques}, year = {2026}, month = jun, volume = {2026}, number = {6}, eid = {097}, pages = {097}, doi = {10.1088/1475-7516/2026/06/097}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026JCAP...06..097Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {clustering, early universe, simulation, theory}, eprint = {2604.01684}, archiveprefix = {arXiv}, primaryclass = {astro-ph.CO}, month_numeric = {6} }

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Why Little Red Dots Disappear at z < 3: Evolution of Number Density and Halo Mass

Chenxuan Zhang, Huanian Zhang, Qingwen Wu, and 2 more authors

arXiv e-prints, Jun 2026

Abs DOI ADS arXiv

A significant puzzle in extragalactic astronomy is the scarcity of Little Red Dots (LRDs) at z 4, LRDs predominantly reside in under-dense regions relative to the general galaxy population. By z ∼3.5, however, this environmental contrast roughly diminishes, and LRDs are found in regions of comparable density to typical galaxies. Simultaneously, the dark matter halo masses of LRDs, inferred from large-scale clustering, grow rapidly from ≲10^10.1 \,M_⊙ at z ∼7.5 to ∼10^11.3 \,M_⊙ at z ∼3.5, where the halo mass becomes close to that of normal galaxies at lower redshift. Applying an empirical stellar-to-halo mass scaling relation, we derive stellar masses for LRDs; these show that black hole masses remain over-massive relative to stellar mass at z > 4, but converge toward the local M_* - M_\rm BH scaling relation by z ∼3.5. The coherent evolution of LRDs’ large- scale environments - as expressed by their overdensity and halo mass - points to a distinct evolutionary pathway from that of normal galaxies. The significantly increased halo masses of LRDs lead to larger galaxy sizes, driven primarily by the potential enhancement of halo spins. Consequently, these sources are no longer as compact as typical high-redshift LRDs. Meanwhile, the depletion of dense gas and/or elevated star formation in their host galaxies would also significantly alter the spectral energy distribution of LRDs.

@article{2026arXiv260602773Z, author = {{Zhang}, Chenxuan and {Zhang}, Huanian and {Wu}, Qingwen and {Ho}, Luis C. and {Wang}, Jian-Min}, title = {{Why Little Red Dots Disappear at z < 3: Evolution of Number Density and Halo Mass}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.02773}, pages = {arXiv:2606.02773}, doi = {10.48550/arXiv.2606.02773}, archiveprefix = {arXiv}, eprint = {2606.02773}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260602773Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, black hole mass, clustering, host galaxy}, month_numeric = {6} }

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Little red dots as a cosmological probe: constraining H_0 with quasi-periodic pulsations

Zijian Zhang, Kohei Inayoshi, Masamune Oguri, and 4 more authors

arXiv e-prints, Jun 2026

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has uncovered a population of “little red dots” (LRDs) at z rsim 4, potentially representing early supermassive black holes embedded in dense gaseous envelopes. The recent discovery of the lensed LRD RXJ2211-RX1 reveals significant variability on rest-frame timescales of decades, which may be interpreted as quasi- periodic variation that has a potential physical parallel to stellar pulsations. In this work, we derive an idealized, self- consistent period-luminosity-temperature (P-L-T_\rm eff) relation based on the hydrostatic envelope model. If this theoretical relation holds and can be empirically validated/calibrated, it would offer a novel framework for constraining the Hubble constant (H_0). The current sparse sampling of \textbackslashtgta\yields a preliminary H_0 = 120.7_-46.5^+47.0 \text km s^-1\text Mpc^-1 as a proof-of-concept, with the error budget dominated by the uncertainty of the pulsation period. Our forecasting analysis shows that continuous monitoring over a 10-year baseline can reduce the H_0 uncertainty to 3-20\%, depending on the intrinsic pulsation period, while the systematic uncertainty floor remains to be fully characterized. This method offers a potential independent probe to measure luminosity distances in the early universe.

@article{2026arXiv260605281Z, author = {{Zhang}, Zijian and {Inayoshi}, Kohei and {Oguri}, Masamune and {Jiang}, Linhua and {Sun}, Fengwu and {Li}, Mingyu and {Lin}, Xiaojing}, title = {{Little red dots as a cosmological probe: constraining $H\_0$ with quasi-periodic pulsations}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, Solar and Stellar Astrophysics}, year = {2026}, month = jun, eid = {arXiv:2606.05281}, pages = {arXiv:2606.05281}, doi = {10.48550/arXiv.2606.05281}, archiveprefix = {arXiv}, eprint = {2606.05281}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260605281Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, theory, variability}, month_numeric = {6} }

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Blackbody Quasar and Radio Source (BBQSORS): A Candidate of Transitional Little Red Dots with a T \ensuremath∼ 10^4 K Blackbody Spectrum

Yuxing Zhong, Xiaoyang Chen, Kohei Ichikawa, and 12 more authors

The Astrophysical Journal Letters, Jun 2026

Abs DOI ADS arXiv

JWST surveys have identified a new class of active galactic nuclei (AGNs) called little red dots (LRDs). Their observational properties challenge the canonical AGN paradigm and provide key insights into the early growth phase of the supermassive black holes (SMBHs). We report Subaru/PFS spectroscopic follow-up of a radio-loud quasar at z = 1.715 from the UNVEIL radio AGN catalog, including X-ray detections. The spectrum displays broad C III]\ensuremathλ1909 and Mg II\ensuremathλ2800 emission lines with FWHM \ensuremath≳4000 km s^\ensuremath-1, accompanied by narrow absorption features. The spectrum reveals a characteristic \ensuremathΛ-shape over the rest- frame wavelength ranging \ensuremath∼1500─3500 Å. The underlying continuum cannot be reproduced by simply applying dust extinction to typical unobscured quasars. Alternatively, it is well described by a blackbody spectrum with a temperature of T \ensuremath∼ 10^4 K. This result agrees well with its UV to MIR photometry, which can be well modeled by three blackbody components representing the BH envelope (T ≍ 9700 K), dust torus (T ≍ 1500 K), and host galaxy dust (T \ensuremath∼ 80 K). The source is marginally detected in the GALEX NUV, revealing a potential V-shaped spectral energy distribution around 1400 Å, reminiscent of the spectral feature reported for LRDs whose V-shapes occur around 3000─4000 Å. This wavelength shift is broadly consistent with the temperature contrast between our blackbody component (T \ensuremath∼ 10^4 K) and the lower effective temperature of T \ensuremath∼ 5000 K expected for the BH envelope of LRDs. These properties suggest that this source might be caught in an evolutionary phase in which the dense gas envelope characteristic of LRD has begun to fragment, allowing us to witness the emergence of a quasar from an LRD-like state.

@article{2026ApJ..1004L...2Z, author = {{Zhong}, Yuxing and {Chen}, Xiaoyang and {Ichikawa}, Kohei and {Kong}, Youwen and {Aoki}, Kentaro and {Yamada}, Satoshi and {Nagao}, Tohru and {Kido}, Daisaburo and {Kawaguchi}, Toshihiro and {Matsuoka}, Yoshiki and {Misawa}, Toru and {Mizukoshi}, Shoichiro and {Onoue}, Masafusa and {Takahashi}, Ayumi and {Toba}, Yoshiki}, title = {{Blackbody Quasar and Radio Source (BBQSORS): A Candidate of Transitional Little Red Dots with a T {\ensuremath{\sim}} {}10$^{4}$ K Blackbody Spectrum}}, journal = {\apjl}, keywords = {Active galactic nuclei, Radio loud quasars, Supermassive black holes, 16, 1349, 1663}, year = {2026}, month = jun, volume = {1004}, number = {1}, eid = {L2}, pages = {L2}, doi = {10.3847/2041-8213/ae633b}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1004L...2Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2603.13736}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {case study, multi-wavelength, radio, sed, spectroscopy}, month_numeric = {6} }

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Little Red Dots as Supermassive Analogs of SS 433

Shuying Zhou, Mouyuan Sun, Xihan Ji, and 11 more authors

arXiv e-prints, Jun 2026

Abs ADS arXiv

High-redshift little red dots (LRDs) are compact sources characterized by V-shaped spectral energy distributions (SEDs), broad emission lines, and often prominent Balmer breaks. Their high number density and apparently large black hole masses suggest that they are essential to the early evolution of galaxies and supermassive black holes (SMBHs); however, the nature of their central engines remains uncertain. Here, we propose that LRDs are the supermassive, high-redshift analogs of the hyper- Eddington accreting Galactic microquasar SS\raisebox-0.5ex\textasciitilde433, viewed at high inclinations. By scaling the hyper-Eddington accretion physics from stellar-mass black holes to supermassive scales, we show that the observed LRD features, including X-ray weakness, soft optical SEDs, apparent sub-Eddington accretion ratio, and Balmer breaks, emerge naturally from the self-shielding geometry of a puffed-up accretion disk. In this framework, the broad-line regions are ionized by anisotropic radiation escaping from the inner disk, analogous to the unseen UV/X-ray emission revealed by the W50 nebula in SS 433. Their low-inclination or lower- accretion-rate counterparts would appear as little blue dots (LBDs) or normal active galactic nuclei. Our model predicts that the Balmer break strength positively correlates with the broad- line width, that the emission lines are more variable than the optical continuum, that LRDs are intrinsically more luminous than observed, and that LBDs are more variable than LRDs. This unified-scale model redefines LRDs as the essential laboratories for observing the rapid accretion-driven growth that shaped the early assembly of galaxies and their central SMBHs.

@article{2026arXiv260621105Z, author = {{Zhou}, Shuying and {Sun}, Mouyuan and {Ji}, Xihan and {Li}, Ya-Ping and {Ho}, Luis C. and {Maiolino}, Roberto and {Cai}, Zhen-Yi and {Feng}, Hai-Cheng and {Fu}, Manqi and {Gu}, Wei-Min and {Liu}, Tong and {Wang}, Junfeng and {Wu}, Jianfeng and {Xue}, Yongquan}, title = {{Little Red Dots as Supermassive Analogs of SS 433}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Astrophysics of Galaxies}, year = {2026}, month = jun, eid = {arXiv:2606.21105}, pages = {arXiv:2606.21105}, archiveprefix = {arXiv}, eprint = {2606.21105}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260621105Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, local counterpart, sed, super-eddington, theory}, month_numeric = {6} }

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The AGN nature of strong C III] emitters in the early Universe with JWST

F. Arevalo-Gonzalez, R. Tripodi, M. Llerena, and 21 more authors

Astronomy & Astrophysics, May 2026

Abs DOI ADS arXiv

The semi-forbidden C III] \ensuremathλ\ensuremathλ1907,1909 doublet is a key tracer of high-ionisation emission in the early Universe. We present a study of C III] emission in galaxies at z = 5 \ensuremath- 7, using publicly available JWST/NIRSpec prism data from programmes including CEERS, JADES, and RUBIES, along with data from the ongoing CAPERS survey. We built a sample of 61 C III]-emitting galaxies, and we classified them as star- forming galaxies (SFGs) or active galactic nucleus (AGN) host galaxies using (1) rest-frame UV and optical emission-line diagnostic diagrams, and (2) the presence or absence of broad Balmer emission lines. The UV diagnostics are based on the combination of the rest-frame equivalent width (EW) of C III] versus the ratio C III]/He II\ensuremathλ1640, and the EW of C IV versus the ratio C IV/He II\ensuremathλ1640. For optical diagnostics, we used the OHNO diagram, which combines four optical emission lines that span a range in ionization potential: [O III] \ensuremathλ5008, H\ensuremathβ, [Ne III] \ensuremathλ3869, and [O II] \ensuremathλ\ensuremathλ3726,3729. We find that it separates AGNs from SFGs with low efficiency. Half of the sources in our sample (29 out of 61 galaxies) exhibit at least one secure indication of AGN activity, while 13 are potential AGNs based on the C III] diagnostic. We derived physical properties, including stellar mass and star formation rate, through spectral energy distribution modelling with BAGPIPES. Our analysis shows that JWST is uncovering a population of strong C III] emitters at high redshift (5 < z < 7) with a median EW of 22.8 Å (16th─84th percentile: 12.5─51.5 Å). This EW exceeds than that of a control sample of C III] emitters at intermediate redshift (3 < z < 4), which have a median EW of 4.7 Å. For the same range of M_UV, the C III] EW increases by \ensuremath∼0.67 dex from 3 < z < 4 to 5 < z < 7, indicating strong redshift evolution in the line strength. We also find that C III] emitters span the full range of the star-forming main sequence, where the majority of galaxies below the sequence have a high C III] EW. Finally, we identify five sources in our sample as little red dots (LRDs) according to the selection criteria in the literature; four of these have already been identified as LRDs, while one is presented here for the first time.

@article{2026A&A...709A..46A, author = {{Arevalo-Gonzalez}, F. and {Tripodi}, R. and {Llerena}, M. and {Pentericci}, L. and {Plat}, A. and {Barro}, G. and {Amor{\'\i}n}, R. O. and {Backhaus}, B. and {Calabr{\`o}}, A. and {Cleri}, N. J. and {Dickinson}, M. and {Dunlop}, J. S. and {Finkelstein}, S. L. and {Giavalisco}, M. and {Hirschmann}, M. and {Kartaltepe}, J. and {Koekemoer}, A. M. and {Lucas}, R. A. and {Napolitano}, L. and {Piconcelli}, E. and {Taylor}, A. J. and {Tombesi}, F. and {Trump}, J. R. and {Wang}, X.}, title = {{The AGN nature of strong C III] emitters in the early Universe with JWST}}, journal = {\aap}, keywords = {techniques: photometric, techniques: spectroscopic, galaxies: active, galaxies: evolution, galaxies: high-redshift, Astrophysics of Galaxies}, year = {2026}, month = may, volume = {709}, eid = {A46}, pages = {A46}, doi = {10.1051/0004-6361/202558652}, archiveprefix = {arXiv}, eprint = {2512.16365}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...709A..46A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, early universe, emission lines, jwst, spectroscopy}, month_numeric = {5} }

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Connecting the Dots: UV-bright Companions of Little Red Dots as Lyman─Werner Sources Enabling Direct-collapse Black Hole Formation

Josephine F. W. Baggen, Matthew T. Scoggins, Pieter van Dokkum, and 3 more authors

The Astrophysical Journal Letters, May 2026

Abs DOI ADS arXiv

We compile a sample of 83 little red dots (LRDs) with JWST imaging and find that a substantial fraction (\ensuremath∼43%, rising to \ensuremath≳80% for the most luminous LRDs) host one or more spatially offset, UV-bright companions at projected separations of 0.5 kpc \ensuremath≲ d \ensuremath≲ 5 kpc, with median = 1.0 kpc. This fraction is even higher when smaller spatial scales are probed at high signal-to-noise ratio: the two most strongly lensed LRDs, A383-LRD1 and the newly discovered A68-LRD1, both have UV- bright companions at separations of only d \ensuremath∼ 0.3 kpc, below the resolution limit of most unlensed JWST samples. We explore whether these ubiquitous red/blue configurations may be physically linked to the formation of LRDs, in analogy with the “synchronized pair” scenario originally proposed for direct-collapse black hole formation. In this picture, UV radiation from the companions, with typically modest stellar masses (M_\ensuremath* \ensuremath∼ 10^8\ensuremath-10^9 M_\ensuremath⊙), suppresses molecular hydrogen cooling in nearby gas, allowing nearly isothermal collapse and the formation of extremely compact objects, such as massive black holes, supermassive stars, or quasi-stars. Using component-resolved photometry and spectral energy distribution modeling, we infer Lyman─Werner radiation fields of J_21,LW \ensuremath∼ 10^2.5─10^5 at the locations of the red components, comparable to those required in direct- collapse models, suggesting that the necessary photodissociation conditions are realized in many LRD systems. This framework provides a simple and self-consistent explanation for the extreme compactness and distinctive spectral properties of LRDs and links long-standing theoretical models for early compact object formation directly to a population now observed with JWST in the early Universe.

@article{2026ApJ..1002L...4B, author = {{Baggen}, Josephine F. W. and {Scoggins}, Matthew T. and {van Dokkum}, Pieter and {Haiman}, Zolt{\'a}n and {Torralba}, Alberto and {Matthee}, Jorryt}, title = {{Connecting the Dots: UV-bright Companions of Little Red Dots as Lyman─Werner Sources Enabling Direct-collapse Black Hole Formation}}, journal = {\apjl}, keywords = {High-redshift galaxies, James Webb Space Telescope, Black hole physics, 734, 2291, 159}, year = {2026}, month = may, volume = {1002}, number = {1}, eid = {L4}, pages = {L4}, doi = {10.3847/2041-8213/ae58a5}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1002L...4B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2602.02702}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {catalog, heavy seed, jwst, sed, theory}, month_numeric = {5} }

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Double Dots: Compact Pairs Mark Little Red Dots and High-Redshift Broad-line AGNs

A. J. Barger and L. L. Cowie

arXiv e-prints, May 2026

Abs ADS arXiv

We utilize JWST imaging of the massive lensing cluster field A2744 to find close pairs of compact sources with separations less than 0.25“. A large fraction of these ”Double Dots“ correspond to Little Red Dots (LRDs) or high-redshift broad-line active galactic nuclei (BLAGNs). Our analysis of 31 identified pairs reveals a median separation of 0.15”. Statistical comparison against a uniform background shows that these are mostly physical pairs. We find that at least 16 of the 24 previously published LRDs in this field (\raisebox-0.5ex\textasciitilde67%) are such pairs, as are both of the high-redshift BLAGNs. We demonstrate that the presence of a companion can significantly contaminate the measured spectral energy distribution, potentially masking the characteristic “v-shape” used for LRD classification. Furthermore, our 2D spectroscopic analysis of several pairs reveals that BLAGN activity is not confined to the redder member of the pair but can originate in either one. Since most LRDs contain broad emission lines, our findings suggest that close pairs are extremely effective markers of galaxies with broad lines at high redshift. We speculate on possible mechanisms, concluding that we are likely seeing merger-driven accretion.

@article{2026arXiv260527903B, author = {{Barger}, A. J. and {Cowie}, L. L.}, title = {{Double Dots: Compact Pairs Mark Little Red Dots and High-Redshift Broad-line AGNs}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.27903}, pages = {arXiv:2605.27903}, archiveprefix = {arXiv}, eprint = {2605.27903}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260527903B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, jwst, morphology, sed, spectroscopy}, month_numeric = {5} }

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A Redshift-based Red Selection of Dusty Star-forming Galaxies

A. J. Barger, L. L. Cowie, S. J. McKay, and 1 more author

arXiv e-prints, May 2026

Abs ADS arXiv

We use JWST observations (1.5 micron to 4.44 micron), together with complete ALMA observations (870 micron and/or 1.2 mm), of the massive lensing cluster field A2744 to show that galaxies between z=1.5 and z=5.5 with rest-frame red colors f_J/f_V > 3 correspond to dusty star-forming galaxies (DSFGs), little red dots (LRDs), and quiescent galaxies. The color selection picks out 34 of the 41 >4.5-sigma ALMA sources in the field (83%). We find that the luminous red sources are generally extended, while the less luminous red sources are almost all compact and correspond to the LRD population. We also find that the great majority of the luminous, extended red sources are DSFGs based on the ALMA data, with a small admixture of quiescent galaxies at z3-sigma level in the ALMA images. Roughly 10% of the DSFGs have high rest-frame X-ray luminosities and must be AGN dominated. The DSFGs and quiescent galaxies nearly all have M_star>10\^{10} solar masses. These massive galaxies become rare at z>5, paralleling the fall off in the number of detected DSFGs.

@article{2026arXiv260524264B, author = {{Barger}, A. J. and {Cowie}, L. L. and {McKay}, S. J. and {Bauer}, F. E.}, title = {{A Redshift-based Red Selection of Dusty Star-forming Galaxies}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.24264}, pages = {arXiv:2605.24264}, archiveprefix = {arXiv}, eprint = {2605.24264}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260524264B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {alma, jwst, morphology, multi-wavelength, sample selection}, month_numeric = {5} }

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From “The Cliff” to “Virgil”: Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec

Guillermo Barro, Pablo G. Pérez-González, Dale Kocevski, and 26 more authors

The Astrophysical Journal, May 2026

Abs DOI ADS arXiv

One of JWST’s most unexpected discoveries is the emergence of “Little Red Dots” (LRDs), compact sources at z \ensuremath≳ 3 with blue rest-frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest early, unusual active galactic nuclei (AGNs). Using a comprehensive photometric selection and public NIRSpec/PRISM spectroscopy across six JWST deep fields, we identify a large sample of 118 LRDs with high-signal-to-noise-ratio spectra, enabling a population-wide analysis of their UV─optical continuum and lines. We find clear correlations between rest- frame UV─optical color ([0.3\ensuremath-0.9 \ensuremathμm]) and slopes; bluer LRDs have blue UV slopes (\ensuremathβ_\ensuremathν,UV \ensuremath∼ 0.3) and red optical slopes, while redder LRDs exhibit redder UV slopes (\ensuremathβ_\ensuremathν,UV \ensuremath∼ 1.1). The continuum shape shows a similar trend; redder LRDs display prominent Balmer breaks and curvature, while bluer LRDs follow power-law-like optical spectral energy distributions. From literature compilations, \ensuremath∼60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission line diagnostics reveal a shift from high H\ensuremathα/H\ensuremathβ and low [O III]\ensuremathλ5007/H\ensuremathβ in redder LRDs to the opposite in bluer ones, along with stronger narrow- line equivalent widths, suggesting a transition from AGN- to host-dominated emission. We fit the spectra with a two-component model combining a gas-enshrouded black hole (BH) and a galaxy host. Redder LRDs require higher-luminosity, unreddened BHs and modestly reddened hosts; bluer LRDs require lower-luminosity, reddened BHs and dust-free galaxies. This framework reproduces the diversity in colors and spectral shape by varying BH luminosity, obscuration, and BH-to-host luminosity ratio.

@article{2026ApJ..1003...96B, author = {{Barro}, Guillermo and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Kocevski}, Dale and {Trump}, Jonathan R. and {Dickinson}, Mark and {Arrabal Haro}, Pablo and {Brooks}, Madisyn and {Donnan}, Callum T. and {Dunlop}, James S. and {Finkelstein}, Steven L. and {Franco}, Maximilien and {Gandolfi}, Giovanni and {Giavalisco}, Mauro and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Larson}, Rebecca L. and {Leung}, Gene C. K. and {Lucas}, Ray A. and {McGrath}, Elizabeth J. and {Papovich}, Casey and {P{\'e}rez-D{\'\i}az}, Borja and {Somerville}, Rachel S. and {Taylor}, Elizabeth and {Taylor}, Anthony J. and {Tripodi}, Roberta and {Yung}, L. Y. Aaron and {Wang}, Xin}, title = {{From ``The Cliff'' to ``Virgil'': Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec}}, journal = {\apj}, keywords = {AGN host galaxies, Extragalactic astronomy, Active galactic nuclei, 2017, 506, 16, Astrophysics of Galaxies}, year = {2026}, month = may, volume = {1003}, number = {1}, eid = {96}, pages = {96}, doi = {10.3847/1538-4357/ae5d2c}, archiveprefix = {arXiv}, eprint = {2512.15853}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1003...96B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, emission lines, jwst, sed, spectroscopy}, month_numeric = {5} }

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Ultraviolet diversity of Little Red Dots as a probe for direct-collapse black hole ages

Elia Cenci, Melanie Habouzit, and Dale D. Kocevski

arXiv e-prints, May 2026

Abs DOI ADS arXiv

Little Red Dots (LRDs) uncovered by the James Webb Space Telescope have been proposed as candidate galaxies hosting embedded accreting direct-collapse black holes (DCBHs), yet the relative ultraviolet (UV) emission of their host galaxy remains highly uncertain and diverse across the population. Using a large-scale cosmological hydrodynamical simulation from the MELIORA suite, we investigate the contribution of PopIII stars and accreting DCBHs in LRD candidates at z>8.5, in the rest-frame 0.2-0.6~μ\mathrmm band. We find that the UV emission from the host galaxy evolves rapidly over the first ∼30~\mathrmMyr following DCBH formation, reflecting the build- up of stellar mass and metal enrichment. This evolution consists of a rapid transition from initially BH-dominated systems, with negligible stellar mass, low metallicity, and high accretion rates, to progressively more developed hosts in which rapid star formation enhances the UV output and metallicity increases. After ∼30~\mathrmMyr, the stellar continuum typically overwhelms the accreting DCBH contribution, producing bluer colours and more extended stellar distributions. As a result, UV-bright LRDs are predicted to host older DCBHs, have higher gas-phase metallicities, lower BH-to-stellar mass ratios, and lower Eddington ratios. The short-lived nature of the LRD phase places strong constraints on their emergence over cosmic time. Overall, our results suggest that DCBH ages can be constrained from the host galaxy contribution to the UV-optical spectrum of LRDs, relative to that of the accreting DCBH, and support the picture in which a DCBH evolutionary sequence is systematically encoded in emission line properties, gas-phase metallicities, and accretion states.

@article{2026arXiv260600205C, author = {{Cenci}, Elia and {Habouzit}, Melanie and {Kocevski}, Dale D.}, title = {{Ultraviolet diversity of Little Red Dots as a probe for direct-collapse black hole ages}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2606.00205}, pages = {arXiv:2606.00205}, doi = {10.48550/arXiv.2606.00205}, archiveprefix = {arXiv}, eprint = {2606.00205}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260600205C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, early universe, heavy seed, host galaxy, simulation}, month_numeric = {5} }

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Super-Eddington accretion of black holes in early nuclear bursts gives birth to Little Red Dots

Yangyao Chen and Houjun Mo

arXiv e-prints, May 2026

Abs DOI ADS arXiv

In a recent paper, Chen et al. developed a framework for modeling the seeding and growth of supermassive black holes (BHs) in the context of ΛCDM cosmogony. Here, we use a set of physically motivated criteria to select a population of predicted BHs and link them to Little Red Dots (LRDs) discovered by JWST. We show that the LRD population at high redshift (z) emerges naturally from a subset of BHs with super-Eddington accretion during nuclear bursts. The model suggests that the observed LRDs are the “tip of the iceberg” of a much larger population of less luminous BHs in the same subset. The model makes specific predictions for the LRD population, such as the mass distributions of their BHs and host galaxies/halos, and the piece-wise redshift evolution of their number density. The cosmological context of the model also allows us to link the observed LRD population to their progenitors (their BH seeds) and lower-z descendant BHs, galaxies and halos. Most LRDs at z∼5 are seeded at z rsim 20 through direct-collapse BHs or pair-instability supernovae from Pop-III stars, and have grown to M_\rm BH ≈10^5–10^7\,\rm M_⊙through nuclear bursts by their observed redshift. LRDs are predicted to have diverse descendants, ranging from compact dwarf galaxies to brightest cluster galaxies (BCGs) at z=0. These predictions are consistent with current observations and can be further tested. The success of this model indicates that the results presented here provide a robust foundation for building detailed models of the LRD population.

@article{2026arXiv260531077C, author = {{Chen}, Yangyao and {Mo}, Houjun}, title = {{Super-Eddington accretion of black holes in early nuclear bursts gives birth to Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.31077}, pages = {arXiv:2605.31077}, doi = {10.48550/arXiv.2605.31077}, archiveprefix = {arXiv}, eprint = {2605.31077}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260531077C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, early universe, heavy seed, super-eddington, theory}, month_numeric = {5} }

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OCEANS of Absorption: High-resolution NIRSpec Spectroscopy Reveals Diverse Balmer-line Absorption in Little Red Dots

Kelcey Davis, Madisyn Brooks, Raymond C. Simons, and 24 more authors

arXiv e-prints, May 2026

Abs DOI ADS arXiv

The “Little Red Dots’ (LRDs) that appeared in JWST deep field images have been the subject of significant study since their discovery. In this work, we present high-resolution follow-up spectroscopy from the OCEANS program of 10 LRDs with Ha coverage at 3<z<7 in the CEERS/EGS field. We find Balmer-line absorption in 4 of these LRDs, a detection rate higher than the fractions reported in lower-resolution NIRSpec surveys. All of the absorbers are presented in high-resolution for the first time here and two have Balmer-line absorption detected for the first time. Of the 10 LRDs, 7 are best fit by Ha profiles with exponential wings. We find that absorbers tend to be blue- shifted with a median velocity offset of (-49 km/s) and absorption equivalent width of 5.3 Angstroms. Trends are explored to compare LRD absorption properties along the sequence of LRDs. We confirm an LRD with statistically significant absorption velocity offsets between Ha and Hb. The diversity of absorption properties can be effectively explained by a model with a radial distribution of partial-covering absorbing gas that is often co-located near the broad-line emission regions, along with a radial gradient of close inflow and distant outflow velocities for the absorbing gas. We present other interesting LRDs, including an outflow-dominated LRD and an LRD with relatively blue UV-to-optical colors but clear Balmer-line absorption. This high occurrence of absorbing hydrogen in LRDs, evident by both the Balmer-line absorption features and Balmer break strengths, implies a near-ubiquitous presence of dense, excited n=2 hydrogen.

@article{2026arXiv260600258D, author = {{Davis}, Kelcey and {Brooks}, Madisyn and {Simons}, Raymond C. and {Trump}, Jonathan R. and {Barro}, Guillermo and {Arrabal Haro}, Pablo and {Backhaus}, Bren E. and {Cleri}, Nikko J. and {de la Vega}, Alexander and {Finkelstein}, Steven L. and {Giavalisco}, Mauro and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Hutchison}, Taylor A. and {Kocevski}, Dale and {Koekemoer}, Anton M. and {Lambrides}, Erini and {Llerena}, Mario and {Lucas}, Ray A. and {Marshall}, Madeline A. and {McGrath}, Elizabeth J. and {Papovich}, Casey and {Starrs}, Aidan and {Taylor}, Anthony J. and {Upton Sanderbeck}, Phoebe R. and {Wang}, Xin and {Wuyts}, Stijn}, title = {{OCEANS of Absorption: High-resolution NIRSpec Spectroscopy Reveals Diverse Balmer-line Absorption in Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2606.00258}, pages = {arXiv:2606.00258}, doi = {10.48550/arXiv.2606.00258}, archiveprefix = {arXiv}, eprint = {2606.00258}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260600258D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, early universe, jwst, kinematics, spectroscopy}, month_numeric = {5} }

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Discovery of low-redshift analogues to little red dots in DESI: A possible later evolutionary stage of compact LRDs

Weiyu Ding, Xu Kong, Wei-Jian Guo, and 8 more authors

Astronomy & Astrophysics, May 2026

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has recently discovered a population of compact red sources at z \ensuremath≥ 4 known as little red dots (LRDs). They are characterized by their V-shaped continuum spectra and prominent broad Balmer emission lines. As their underlying physical nature remains debated, and direct study at high redshift is challenging, we seek to identify and characterize LRD analogues in the low-redshift universe to constrain their properties and potential evolutionary pathways. We identified five candidates at z = 0.2 \ensuremath- 0.4 from the Dark Energy Spectroscopic Instrument (DESI) that exhibit spectral energy distributions (SEDs) and broad Balmer emission lines closely resembling their high-redshift counterparts. However, we find significant differences: our low-redshift sample occupies a different region on the Baldwin, Phillips & Terlevich (BPT) diagram, and their stellar masses are significantly higher, suggesting a more substantial host galaxy contribution. These sources are not necessarily direct local analogues of high-redshift LRDs, but may represent later evolutionary stages of compact rapidly accreting systems or systems with related observational properties arising under different physical conditions. This sample provides a valuable laboratory for detailed follow-up studies to elucidate the nature of LRD-like phenomena.

@article{2026A&A...709L..11D, author = {{Ding}, Weiyu and {Kong}, Xu and {Guo}, Wei-Jian and {Zou}, Hu and {Wang}, Jialai and {Li}, Fujia and {Zhang}, Hongxin and {Song}, Jie and {Zhang}, Jingyi and {Li}, Niu and {Li}, Wen-Xiong}, title = {{Discovery of low-redshift analogues to little red dots in DESI: A possible later evolutionary stage of compact LRDs}}, journal = {\aap}, keywords = {quasars: emission lines, quasars: supermassive black holes, Astrophysics of Galaxies}, year = {2026}, month = may, volume = {709}, eid = {L11}, pages = {L11}, doi = {10.1051/0004-6361/202557889}, archiveprefix = {arXiv}, eprint = {2604.14551}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...709L..11D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, host galaxy, local counterpart, sed, spectroscopy}, month_numeric = {5} }

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A Rapid Evolution in the Observed Mbh/M* Relation at z > 3 Revealed via Spectro-photometric SED-Modeling

Ansh R. Gupta, Anthony Taylor, Emma Curtis-Lake, and 33 more authors

arXiv e-prints, May 2026

Abs DOI ADS arXiv

Spectroscopic observations from JWST have uncovered a plethora of active galactic nuclei (AGN) at z > 4 with black hole (BH) mass (Mbh) to stellar mass (M*) ratios significantly above the local relation when using standard virial mass scaling relations. However, M* estimates of AGN may be inaccurate due to limitations in spectral energy distribution (SED) fitting codes, exemplified by a lack of physically-motivated AGN line emission models. Here, we fit NIRSpec/PRISM spectra of 39 galaxies at z \raisebox-0.5ex~3.5-7 selected as broad-line AGN from the CEERS and RUBIES surveys. Applying kinematic decompositions from NIRSpec/G395M spectra, we fit their continuum and narrow-component line fluxes using the BEAGLE-AGN SED fitting tool. While limitations of BEAGLE-AGN make it difficult to model little red dots (LRDs), we find that M* estimates of non-LRDs are, surprisingly, only modestly impacted by the inclusion or not of AGN narrow-line region (NLR) and continuum emission model components. We further find that non- LRD AGN at z 4.5 display elevated ratios. While we cannot rule out observational biases or systematic uncertainties as partial causes, this transition over just \raisebox-0.5ex\textasciitilde500 Myr is driven entirely by changes in M* rather than an evolving Mbh distribution. These findings are consistent with models in which rapid BH growth results in elevated Mbh/M* ratios at early times, with a swift late-time assembly of host galaxies returning sources to the local relation at z < 4.

@article{2026arXiv260530414G, author = {{Gupta}, Ansh R. and {Taylor}, Anthony and {Curtis-Lake}, Emma and {Silcock}, Maddie and {Ch{\'a}vez Ortiz}, {\'O}scar A. and {Finkelstein}, Steven L. and {Akins}, Hollis B. and {Backhaus}, Bren E. and {Barro}, Guillermo and {Bisigello}, Laura and {Brooks}, Madisyn and {Casey}, Caitlin M. and {Charlot}, Stephane and {Chevallard}, Jacopo and {Feltre}, Anna and {Gandolfi}, Giovanni and {Giavalisco}, Mauro and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Hsiao}, Tiger Yu-Yang and {Jeon}, Junehyoung and {Jogee}, Shardha and {Kartaltepe}, Jeyhan S. and {Kocevski}, Dale D. and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Leung}, Gene C. K. and {Lucas}, Ray A. and {Pacucci}, Fabio and {Pirzkal}, Nor and {Plat}, Adele and {Somerville}, Rachel S. and {Trump}, Jonathan R. and {Vidal-Garc{\'\i}a}, Alba and {Wang}, Xin and {Yung}, L. Y. Aaron}, title = {{A Rapid Evolution in the Observed Mbh/M* Relation at z > 3 Revealed via Spectro-photometric SED-Modeling}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.30414}, pages = {arXiv:2605.30414}, doi = {10.48550/arXiv.2605.30414}, archiveprefix = {arXiv}, eprint = {2605.30414}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260530414G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, sed}, month_numeric = {5} }

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The Emergence of Little Red Dots from Binary Massive Black Holes

Kohei Inayoshi, Jinyi Shangguan, Xian Chen, and 2 more authors

The Astrophysical Journal, May 2026

Abs DOI ADS arXiv

Little red dots (LRDs) are a newly identified class of broad-line active galactic nuclei (AGNs) with a distinctive V-shaped spectrum characterized by red optical and blue UV continuum emission. Their high abundance at redshifts of z \ensuremath∼ 6─8 and decline at lower redshifts suggest a transient origin. We propose that the spectral shape of LRDs originates from compact binary black hole systems, in which each black hole is surrounded by a mini-disk and embedded within a larger circumbinary disk. With a binary separation of \ensuremath≲10^3 Schwarzschild radii, the Wien tail of a T ≃ 5000 K blackbody spectrum at the inner edge of the circumbinary disk produces the red optical emission, while the mini-disks power the UV continuum. Binary torques carve out a gap between the circumbinary disk and the mini-disks, setting the turnover wavelength of the V-shaped spectrum around the Balmer limit. This scenario naturally reproduces LRD spectra requiring only modest dust attenuation (A_V \ensuremath≲ 1 mag), resolving overestimated luminosities for LRDs in previous studies and alleviating a tension with the so-called Sołtan argument. This model predicts distinct spectral evolution as the binary orbit decays through binary disk interactions and gravitational-wave (GW) emission, linking early-stage “proto-LRD” binaries to the broader AGN population and late-stage “LRD descendants” to coalescing binaries detectable in GW experiments.

@article{2026ApJ..1002...25I, author = {{Inayoshi}, Kohei and {Shangguan}, Jinyi and {Chen}, Xian and {Ho}, Luis C. and {Haiman}, Zolt{\'a}n}, title = {{The Emergence of Little Red Dots from Binary Massive Black Holes}}, journal = {\apj}, keywords = {Supermassive black holes, Quasars, High-redshift galaxies, 1663, 1319, 734}, year = {2026}, month = may, volume = {1002}, number = {1}, eid = {25}, pages = {25}, doi = {10.3847/1538-4357/ae548d}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1002...25I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2505.05322}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, lrdkeys = {agn-dominated, early universe, sed, theory}, month_numeric = {5} }

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A direct black-hole mass measurement in a little red dot at high redshift

Ignas Juodžbalis, Cosimo Marconcini, Francesco D’Eugenio, and 37 more authors

Nature, May 2026

Abs DOI ADS arXiv

Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad H\ensuremathα emitters with optically red continua, named little red dots (LRDs)^1, which comprise 15─30% of the high-redshift broad-line AGN population^2. Owing to their peculiar properties^3, 4, 5─6, modelling LRDs with standard AGN scenarios has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black-hole masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to two orders of magnitude^7, 8, 9─10. Here we report a direct, dynamical black-hole mass measurement in a strongly lensed LRD at a redshift of 7.04. The combination of lensing with deep spectroscopic data reveals a rotation curve that is inconsistent with a nuclear star cluster, yet can be well explained by Keplerian rotation around a point mass of 50 million solar masses, consistent with virial black-hole mass estimates. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer M_BH/M_\textasteriskcentered > 2 (where M_BH is the black-hole mass and M_\textasteriskcentered is the stellar mass). Such a ’naked’ black hole, together with its near-pristine environment^11, indicates that this LRD is a massive black-hole seed caught in its earliest accretion phase.

@article{2026Natur.653.1017J, author = {{Juod{\v{z}}balis}, Ignas and {Marconcini}, Cosimo and {D'Eugenio}, Francesco and {Maiolino}, Roberto and {Marconi}, Alessandro and {{\"U}bler}, Hannah and {Scholtz}, Jan and {Ji}, Xihan and {Jones}, Gareth C. and {Perna}, Michele and {Arribas}, Santiago and {Bennett}, Jake S. and {Bromm}, Volker and {Bunker}, Andrew J. and {Carniani}, Stefano and {Charlot}, St{\'e}phane and {Cresci}, Giovanni and {Dayal}, Pratika and {Egami}, Eiichi and {Fabian}, Andrew and {Inayoshi}, Kohei and {Isobe}, Yuki and {Ivey}, Lucy R. and {Koudmani}, Sophie and {Laporte}, Nicolas and {Liu}, Boyuan and {Lyu}, Jianwei and {Mazzolari}, Giovanni and {Monty}, Stephanie and {Parlanti}, Eleonora and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Robertson}, Brant and {Schneider}, Raffaella and {Sijacki}, Debora and {Tacchella}, Sandro and {Trinca}, Alessandro and {Valiante}, Rosa and {Volonteri}, Marta and {Witstok}, Joris and {Zhang}, Saiyang}, title = {{A direct black-hole mass measurement in a little red dot at high redshift}}, journal = {\nat}, keywords = {Physical Sciences, Astronomical and Space Sciences}, year = {2026}, month = may, volume = {653}, number = {8116}, pages = {1017-1021}, doi = {10.1038/s41586-026-10579-4}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026Natur.653.1017J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2508.21748}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {black hole mass, early universe, heavy seed, kinematics, spectroscopy}, month_numeric = {5} }

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(LRDs)^2: The Low-ReDshift Little Red Dots Survey. II. DESI DR1 Sample

Xiaojing Lin, Xiaohui Fan, Zheng Cai, and 12 more authors

arXiv e-prints, May 2026

Abs DOI ADS arXiv

JWST has revealed a substantial population of “Little Red Dots” (LRDs) at z>4, challenging conventional AGN frameworks. However, the low-redshift regime remains largely unexplored. In the second paper of the (LRDs)^2 series, we present a systematic selection from DESI DR1 and identify 27 LRDs at z=0.2-0.9, yielding a number density lower limit of 7.5 \times 10^-10 cMpc^-3. We conducted near-IR spectroscopic follow-up observations for 18 of them, revealing their full SED shapes and emission lines. These low-z LRDs share the hallmark properties of their high-z counterparts: compact morphology, V-shaped UV- optical continua, broad Balmer emission with extreme decrements (median Hα/Hβ∼16), frequent Balmer absorption (67%), and blackbody-like optical-to-near-IR continua. All have low metallicity, occupy the same regions in the BPT diagram as high-z LRDs, and have softer ionizing spectra than typical AGNs. The consistency between low-z and high-z LRD properties indicates the same physical processes at work. The correlation between broad-line Balmer luminosity and L_5100 deviates from that of local type-1 AGNs, limiting the direct application of local BH mass calibrations. Ionized [O III] outflows are ubiquitous (78%). One LRD at z=0.196, J1717+3807, shows robust long-term variability in i and WISE bands. The optical-to-NIR continua of LRDs reveal a wide range of temperatures ∼2000-4700 K (peak 0.6-1.5 μm), with a subset showing cooler and larger envelopes than those at high z. Low-z LRDs serve not only as proximate laboratories for probing the nature of LRDs, but also trace the cosmic evolution of this population from the cosmic dawn to the present day.

@article{2026arXiv260521574L, author = {{Lin}, Xiaojing and {Fan}, Xiaohui and {Cai}, Zheng and {Liu}, Yichen and {Sun}, Fengwu and {Bian}, Fuyan and {Li}, Mingyu and {Mao}, Junjie and {Greene}, Jenny E. and {Liu}, Hanpu and {Li}, Jiaxuan and {Liu}, Weizhe and {Ma}, Yilun and {Sun}, Zechang and {Zhang}, Zijian}, title = {{(LRDs)$^2$: The Low-ReDshift Little Red Dots Survey. II. DESI DR1 Sample}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.21574}, pages = {arXiv:2605.21574}, doi = {10.48550/arXiv.2605.21574}, archiveprefix = {arXiv}, eprint = {2605.21574}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260521574L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {catalog, emission lines, local counterpart, sed, spectroscopy}, month_numeric = {5} }

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COSMOS-3D: Dense Circumnuclear Gas Across Black Hole Growth Phases at z \ensuremath∼ 3

Zi-Jian Li, Siwei Zou, Jianwei Lyu, and 25 more authors

The Astrophysical Journal, May 2026

Abs DOI ADS arXiv

We report the discovery of two broad-line X-ray active galactic nuclei (AGNs) (cid_414 and cid_947) at z \ensuremath∼ 3 identified in the JWST Cycle 3 COSMOS-3D program using NIRCam F444W grism spectroscopy. Both exhibit prominent He I\ensuremathλ10830 +Pa\ensuremathγ emission and absorption, indicative of circumnuclear dense gas that is traced in these systems. Complementary UV and optical spectroscopy in the COSMOS field provides Ly\ensuremathα, Si IV, and C IV measurements. Both sources are detected in MIRI F1000W, and cid_414 is also detected in F2100W, indicating hot dust emission. The two AGNs show distinct black hole and obscuration properties. The source cid_414 displays little red dot (LRD)-like, V-shaped spectral energy distribution with a turnover near the Balmer 4000 Å break and a narrow Ly\ensuremathα line with logLLy\ens uremathα=42.49\ensuremath\pm0.01ergs\ensuremath- 1, with no additional metal lines detected. In contrast, cid_947 exhibits a higher He I\ensuremathλ10830 absorption column density, larger X-ray─inferred N_H, lower intrinsic 2─10 keV luminosity, and strong blueshifted features in He I, Si IV, and C IV absorption with velocity offsets exceeding 5000 km s^\ensuremath-1. Photoionization modeling implies gas densities of \ensuremath∼10^9\ensuremath-10 cm^\ensuremath-3 and sizes comparable to the broad-line region, consistent with dense gas envelopes predicted for LRDs. Together with previous detections of He I\ensuremathλ10830 absorption in compact LRDs, these results suggest that dense circumnuclear gas is likely prevalent at high redshift and may regulate obscuration and black hole─host coevolution across AGN types.

@article{2026ApJ..1002....9L, author = {{Li}, Zi-Jian and {Zou}, Siwei and {Lyu}, Jianwei and {Champagne}, Jaclyn B. and {Huang}, Jia-Sheng and {Cheng}, Cheng and {Fu}, Shuqi and {Zhang}, Zijian and {Jiang}, Danyang and {Lee}, Khee-Gan and {Wang}, Feige and {Fan}, Xiaohui and {Yang}, Jinyi and {Li}, Ruancun and {Akins}, Hollis B. and {Bian}, Fuyan and {Dai}, Y. Sophia and {Faisst}, Andreas L. and {Ho}, Luis C. and {Inayoshi}, Kohei and {Jiang}, Linhua and {Jin}, Xiangyu and {Kakiichi}, Koki and {Kartaltepe}, Jeyhan S. and {Li}, Zihao and {Liu}, Weizhe and {Schindler}, Jan-Torge and {Tee}, Wei Leong}, title = {{COSMOS-3D: Dense Circumnuclear Gas Across Black Hole Growth Phases at z {\ensuremath{\sim}} 3}}, journal = {\apj}, keywords = {Active galactic nuclei, AGN host galaxies, Dust shells, 16, 2017, 414}, year = {2026}, month = may, volume = {1002}, number = {1}, eid = {9}, pages = {9}, doi = {10.3847/1538-4357/ae587b}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1002....9L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2512.02093}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {absorption features, agn-dominated, jwst, obscuration, spectroscopy}, month_numeric = {5} }

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Little red dots as obscured little blue dots: relative abundances, luminosities, and black-hole masses

Piero Madau and Roberto Maiolino

arXiv e-prints, May 2026

Abs DOI ADS arXiv

We test whether “little red dots“ (LRDs) are the dust-reddened, high- inclination counterparts of bluer compact broad-line active galactic nuclei, here referred to as “little blue dots” (LBDs), by modeling their relative number densities and luminosities. Using the observed UV luminosity function (LF) of broad-line active galactic nuclei (BLAGNs) at z>4 as the parent distribution, we forward-model the effects of accretion rate, anisotropic emission, orientation, and dust obscuration within our super-Eddington unification framework. We show that a model with a geometrically thick accretion flow, an equatorially concentrated broad-line region, and a dusty circumnuclear cloud population reproduces the LRD LF over the luminosity range currently constrained by JWST. The predicted LRD/BLAGN fraction is strongly luminosity dependent, rising from 3% at M_1500=-21 to a peak value of 20% near M_1500=-19. The model also predicts a larger apparent LRD fraction at rest-frame optical wavelengths, reaching 26% at M_4500=-20 mag and 35% at M_6500=-21. The best-fitting solutions imply a characteristic per-cloud extinction =2.8\^{+0.0}_{-0.4} mag and a mean dust covering factor = 0.23\^{+0.27}_{-0.00} at 68% confidence, with the asymmetric uncertainties reflecting the degeneracy between cloud extinction and covering factor. These results may support an orientation-based unification of little dots and identify the LRD LF as a key demographic test of rapid accretion onto infant black holes at cosmic dawn. Within this same framework, UV-selected LRDs are predicted to host systematically more massive black holes than unobscured LBDs, not because they represent a distinct parent population, but because dust attenuation preferentially removes lower-mass obscured systems from the observed UV sample.

@article{2026arXiv260505074M, author = {{Madau}, Piero and {Maiolino}, Roberto}, title = {{Little red dots as obscured little blue dots: relative abundances, luminosities, and black-hole masses}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = may, eid = {arXiv:2605.05074}, pages = {arXiv:2605.05074}, doi = {10.48550/arXiv.2605.05074}, archiveprefix = {arXiv}, eprint = {2605.05074}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260505074M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, black hole mass, dust-reddened, super-eddington, theory}, month_numeric = {5} }

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A black hole in a near pristine galaxy 700 Myr after the big bang

Roberto Maiolino, Hannah Übler, Francesco D’Eugenio, and 35 more authors

Monthly Notices of the Royal Astronomical Society, May 2026

Abs DOI ADS arXiv

The recent discovery of a large number of massive black holes within the first two billion years after the big bang, as well as their peculiar properties, have been largely unexpected based on the extrapolation of the properties of luminous quasars. These findings have prompted the development of several theoretical models for the early formation and growth of black holes, which are, however, difficult to differentiate. We report the metallicity measurement around a gravitationally lensed massive black hole at redshift 7.04 (classified as a Little Red Dot), hosted in a galaxy with very low dynamical mass. The weakness of the [O III]5007 emission line relative to the narrow H emission indicates extremely low metallicity, about solar, and even more metal poor in the surrounding few 100 pc. We argue that such properties cannot be uncommon among accreting black holes around this early cosmic epoch. Explaining such a low chemical enrichment in a system that has developed a massive black hole is challenging for most theories. Models assuming heavy black hole seeds (such as Direct Collapse Black Holes) or super- Eddington accretion scenarios struggle to explain the observations, although they can potentially reproduce the observed properties in some cases. Models invoking ’primordial black holes’ (i.e. putative black holes formed shortly after the big bang) may potentially explain the low chemical enrichment associated with this black hole, although this class of models also requires further developments for proper testing.

@article{2026MNRAS.548f2109M, author = {{Maiolino}, Roberto and {{\"U}bler}, Hannah and {D'Eugenio}, Francesco and {Scholtz}, Jan and {Juod{\v{z}}balis}, Ignas and {Ji}, Xihan and {Perna}, Michele and {Bromm}, Volker and {Dayal}, Pratika and {Koudmani}, Sophie and {Liu}, Boyuan and {Schneider}, Raffaella and {Sijacki}, Debora and {Valiante}, Rosa and {Trinca}, Alessandro and {Zhang}, Saiyang and {Volonteri}, Marta and {Inayoshi}, Kohei and {Carniani}, Stefano and {Nakajima}, Kimihiko and {Isobe}, Yuki and {Witstok}, Joris and {Jones}, Gareth C and {Tacchella}, Sandro and {Arribas}, Santiago and {Bunker}, Andrew and {Cataldi}, Elisa and {Charlot}, Stephane and {Curti}, Giovanni Cresci Mirko and {Fabian}, Andrew C and {Katz}, Harley and {Kumari}, Nimisha and {Laporte}, Nicolas and {Mazzolari}, Giovanni and {Robertson}, Brant and {Sun}, Fengwu and {Del Pino}, Bruno Rodriguez and {Venturi}, Giacomo}, title = {{A black hole in a near pristine galaxy 700 Myr after the big bang}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: formation, galaxies: high-redshift, galaxies: nuclei, quasars: emission lines, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2026}, month = may, volume = {548}, number = {1}, eid = {staf2109}, pages = {staf2109}, doi = {10.1093/mnras/staf2109}, archiveprefix = {arXiv}, eprint = {2505.22567}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.548f2109M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, heavy seed, spectroscopy, theory}, month_numeric = {5} }

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A Deep Spectroscopic Study of a JWST-discovered, Faint, Broad-line AGN at z \ensuremath∼ 5

Elaina Malczewski, Feige Wang, Jinyi Yang, and 8 more authors

Research Notes of the American Astronomical Society, May 2026

Abs DOI ADS

In this work, we present deep NIRSpec/PRISM and NIRSpec/G395M observations of J0910M0414-BHAE-1, a broad-line active galactic nucleus at z = 4.910 \ensuremath\pm 0.003 initially discovered with NIRCam/WFSS. We detect rest-frame UV (e.g., Ly\ensuremathα, C IV, C III], Mg II) and optical (H\ensuremathγ, H\ensuremathβ, H\ensuremathα, and [O III]) lines. By modeling the H\ensuremathα line, we measure FWHM = 3351 \ensuremath\pm 66 km s^\ensuremath-1, implying a supermassive black hole with log(MBH/M\ensuremath⊙)=8.14\ensuremath\pm0.02. The bolometric luminosity (from the broad H\ensuremathα) is (2.23 \ensuremath\pm 0.09) \texttimes 10^45 erg s^\ensuremath-1 with an Eddington ratio of 0.11 \ensuremath\pm 0.01. The errors do not include the \ensuremath∼0.3─0.5 dex systematic uncertainty of the single-epoch virial method. Comparing the object’s spectral energy distribution to those of quasars and Little Red Dots suggests that the object bridges the gap between these classes.

@article{2026RNAAS..10..122M, author = {{Malczewski}, Elaina and {Wang}, Feige and {Yang}, Jinyi and {Barth}, Aaron J. and {Champagne}, Jaclyn B. and {Fan}, Xiaohui and {Gloudemans}, Anniek J. and {Jin}, Xiangyu and {Li}, Jiang-Tao and {Lupi}, Alessandro and {Mazzucchelli}, Chiara}, title = {{A Deep Spectroscopic Study of a JWST-discovered, Faint, Broad-line AGN at z {\ensuremath{\sim}} 5}}, journal = {Research Notes of the American Astronomical Society}, keywords = {Active galactic nuclei, Supermassive black holes, Galaxy evolution, 16, 1663, 594}, year = {2026}, month = may, volume = {10}, number = {5}, eid = {122}, pages = {122}, doi = {10.3847/2515-5172/ae6b88}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026RNAAS..10..122M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, case study, jwst, spectroscopy}, month_numeric = {5} }

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Little Red Dots on FIRE: The Ability of Bursty Galaxies to Host an Abundant Population of High-redshift AGN

Andrew Marszewski, Claude-André Faucher-Giguère, Guochao Sun, and 5 more authors

The Astrophysical Journal Letters, May 2026

Abs DOI ADS arXiv

The James Webb Space Telescope has unveiled an abundant population of potential active galactic nuclei (AGN) at high redshift (z \ensuremath≳ 4) known as little red dots (LRDs), which are likely hosted in relatively low-mass galaxies. However, previous theoretical models have highlighted the difficulty in continuously feeding massive black holes in the central regions of bursty, high-redshift galaxies because of repeated gas evacuation by stellar feedback. We analyze galaxies in high- redshift FIRE-2 simulations to understand whether they are capable of hosting the observed abundant population of high- redshift AGN. We use a gravitational torque-driven accretion (GTDA) model and a simple freefall accretion model to derive black hole accretion rates and construct predicted AGN bolometric luminosity functions for z = 5─7. The GTDA model and the freefall model with black holes accreting \ensuremath≲1% of their central gas supply (<100 pc) per freefall time predict AGN abundances that are more than sufficient to explain the most recent LRD observations. The fiducial models, in fact, overpredict the number of low- luminosity AGN as compared with observations. We explore possible resolutions of this tension. A plausible, though likely not unique, scenario for alleviating the AGN overpredictions, which also provides a good match to the host-galaxy UV luminosity distribution, suggests that LRDs are super-Eddington- accreting, Eddington-luminosity-limited, M_BH \ensuremath≳ 2 \texttimes 10^5 M_\ensuremath⊙ black holes residing in M_\ensuremath⋆ \ensuremath≳ 2 \texttimes 10^7 M_\ensuremath⊙ galaxies. We show that, under simple assumptions, mock observations of such sources can reproduce key observed LRD characteristics.

@article{2026ApJ..1002L..13M, author = {{Marszewski}, Andrew and {Faucher-Gigu{\`e}re}, Claude-Andr{\'e} and {Sun}, Guochao and {Angl{\'e}s-Alc{\'a}zar}, Daniel and {Feldmann}, Robert and {Su}, Kung-Yi and {Miller}, Tim B. and {Roy}, Niranjan Chandra}, title = {{Little Red Dots on FIRE: The Ability of Bursty Galaxies to Host an Abundant Population of High-redshift AGN}}, journal = {\apjl}, keywords = {High-redshift galaxies, Galaxies, AGN host galaxies, Galaxy formation, Astrophysical black holes, Supermassive black holes, Hydrodynamical simulations, Black holes, Astronomical simulations, 734, 573, 2017, 595, 98, 1663, 767, 162, 1857}, year = {2026}, month = may, volume = {1002}, number = {1}, eid = {L13}, pages = {L13}, doi = {10.3847/2041-8213/ae5d45}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1002L..13M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2601.22213}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {abundance, early universe, simulation, super-eddington, theory}, month_numeric = {5} }

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Non-LTE atmosphere models of very luminous sources and their applicability to Little Red Dots, quasi-stars, and similar objects

Fabrice Martins, Daniel Schaerer, and Rui Marques-Chaves

arXiv e-prints, May 2026

Abs ADS arXiv

We investigate whether atmosphere models traditionally used for massive stars with strong winds can produce synthetic spectra morphologically similar to those of Little Red Dots (LRDs). We compute atmosphere models and synthetic spectra with the code CMFGEN. The models assume a thermalized radiation field at the inner boundary, parameterized by a temperature varying between 5000 and 12000\raisebox-0.5ex\textasciitildeK. We adopt a typical luminosity of 1e10 Lsun. The models are spherical, assume an expanding atmosphere, and are computed under non-LTE conditions and for several metallicities. The spectral energy distribution (SED) is different from a blackbody, with a blue optical spectrum. Broad hydrogen emission lines are produced, their wings being formed by electron scattering. The SED near the Balmer and Paschen limit is rather continuous. A Balmer break is predicted for the coolest temperature models provided the wind density is reduced. The SED and Balmer decrement of most LRDs is reproduced by the models, provided they are dust- attenuated with Av\raisebox-0.5ex\textasciitilde1.9-2.7. Assuming the absorbed luminosity is re-radiated in the infrared, the energy output at these wavelengths is consistent with observational constraints. The models predict FeII, oxygen and calcium lines. OI lines at 8446 A and 1.129 um are produced mostly by Lybeta fluorescence. The strength of emission lines from metals depends on input temperature, metallicity, and details of the radiative transfer models. CMFGEN atmosphere models predict a large number of spectral properties observed in many LRDs. They struggle to simultaneously produce a genuine Balmer break and strong emission lines. Whether they are more relevant or not to explain LRDs’ spectra compared to alternative models is unclear, leaving open the question of the physical conditions in LRDs.

@article{2026arXiv260512141M, author = {{Martins}, Fabrice and {Schaerer}, Daniel and {Marques-Chaves}, Rui}, title = {{Non-LTE atmosphere models of very luminous sources and their applicability to Little Red Dots, quasi-stars, and similar objects}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.12141}, pages = {arXiv:2605.12141}, archiveprefix = {arXiv}, eprint = {2605.12141}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260512141M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, exotic physics, non-agn, sed, simulation}, month_numeric = {5} }

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A new sample of Little Red Dots at z<0.45 in DESI DR1: Broad Balmer lines, low ionization spectrum and no variability

Kevin Park, Alberto Torralba, Jorryt Matthee, and 4 more authors

arXiv e-prints, May 2026

Abs ADS arXiv

JWST has unveiled an abundant population of compact broad-line emitters largely at zrsim4, the Little Red Dots (LRDs), which might represent a previously unprobed supermassive black hole evolution channel predominant at high redshift. However, the LRDs have remained mostly elusive at lower redshift (z\lesssim2) where detailed studies are possible from ground- based observatories. We searched for low-redshift LRDs in the Dark Energy Spectroscopic Instrument (DESI) survey. Our search is primarily based on emission line properties, as opposed to earlier approaches that searched for compact sources with specific photometric spectral energy distributions. We report the discovery of eight LRDs at z=0.2-0.45, which show spectral features akin to the high-redshift LRDs in the rest-frame optical. The sources are characterized by broad Balmer lines, steep Balmer decrements, compact morphologies, Balmer absorption features and/or strong He I emission, but weak or absent He II, [Ne V] or other high excitation lines typical of Type I AGN. For 7 out of 8 sources, we retrieve dense-cadence light curves from time-domain surveys and for most sources we find weak to no intrinsic variability (0.0-0.1 mag) over 4-17 years in the rest-frame. We also highlight the identification of a quasar with similar Balmer line profiles as LRDs, but shows differences in Balmer decrement, significant variability, and high- ionisation lines. Given the effective volume 4.9\rm Gpc^3 covered by DESI DR1 at z<0.45, our sample corresponds to a number density of 1.6\times10^-9Mpc^-3, indicating a number density \sim10,000 times lower than in the first billion years of cosmic time. We find a dearth of luminous and red LRDs at z<1 compared to higher-redshift, which could suggest lower gas feeding rates of LRD activity due to higher metallicities at later cosmic epochs.

@article{2026arXiv260514233P, author = {{Park}, Kevin and {Torralba}, Alberto and {Matthee}, Jorryt and {Mascia}, Sara and {Haiman}, Zolt{\'a}n and {Naidu}, Rohan P. and {de Graaff}, Anna}, title = {{A new sample of Little Red Dots at $z<0.45$ in DESI DR1: Broad Balmer lines, low ionization spectrum and no variability}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.14233}, pages = {arXiv:2605.14233}, archiveprefix = {arXiv}, eprint = {2605.14233}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260514233P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, catalog, emission lines, local counterpart, variability}, month_numeric = {5} }

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Little Red Dots from ultra-strongly self-interacting dark matter

M. Grant Roberts, Lila Braff, Aarna Garg, and 2 more authors

\jcap, May 2026

Abs DOI ADS arXiv

We investigate the possibility that the recently identified population of high-redshift, obscured quasars — known as “Little Red Dots” (LRDs) — originates from early black hole seed formation driven by ultra-strongly self- interacting dark matter (uSIDM). In this framework, dark matter halos undergo gravothermal core collapse due to large self- interaction cross sections, resulting in the rapid formation of massive black hole (BH) seeds with masses \ensuremath≳ 10^5 M _\ensuremath⊙ at redshifts z \ensuremath≳ 5. We develop a semi-analytic model that tracks the evolution of the dark matter halo population, the redshift of collapse z _coll, and the corresponding BH mass function. Black hole growth is modeled stochastically via a log- normal Eddington ratio distribution and a finite duty cycle. We find that the uSIDM scenario naturally reproduces key observed properties of LRDs, including their abundance, compactness, and characteristic BH masses, while offering a mechanism for early, obscured black hole formation that is difficult to achieve in standard CDM-based models. The predicted SMBH mass function at z \ensuremath∼ 5 shows excellent agreement with LRD observational data and SIDM merger-tree simulations, particularly at the high-mass end (m _BH \ensuremath≳ 10^7 M _\ensuremath⊙). These results suggest that LRDs may serve as powerful observational tracers of exotic dark sector physics and that SMBH formation in the early universe could be significantly shaped by non-gravitational dark matter interactions.

@article{2026JCAP...05..003R, author = {{Roberts}, M. Grant and {Braff}, Lila and {Garg}, Aarna and {Profumo}, Stefano and {Jeltema}, Tesla}, title = {{Little Red Dots from ultra-strongly self-interacting dark matter}}, journal = {\jcap}, keywords = {dark matter theory, massive black holes, semi-analytic modeling, Statistical sampling techniques, Astrophysics of Galaxies}, year = {2026}, month = may, volume = {2026}, number = {5}, eid = {003}, pages = {003}, doi = {10.1088/1475-7516/2026/05/003}, archiveprefix = {arXiv}, eprint = {2507.03230}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026JCAP...05..003R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, early universe, exotic physics, heavy seed, theory}, month_numeric = {5} }

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Halo-driven Origin and Suppression of Over-massive Black Holes and Little Red Dots

Ritik Sharma and Mahavir Sharma

arXiv e-prints, May 2026

Abs ADS arXiv

We present a theoretical model in which the recently detected over- massive black holes (OBHs), and possibly Little Red Dots (LRDs), arise during a halo-driven transient phase preceding the established coevolution of supermassive black holes (SMBHs) and their host galaxies. In this model, halo gravity drives an early phase of rapid black hole growth, leading to systems in high- redshift haloes that lie above the local scaling relations. As the halo evolves, a transition in halo thermodynamics leads to the onset of a hot, pressure-supported medium that suppresses accretion, reducing the black hole growth rate and driving the system toward the local black hole mass-stellar mass relation. LRDs may represent an observational manifestation of the rapid, halo-driven growth phase, while OBHs trace its direct mass signature. Our model thus provides a unified framework in which these systems form and evolve toward the regulated coevolution observed in the local Universe.

@article{2026arXiv260516485S, author = {{Sharma}, Ritik and {Sharma}, Mahavir}, title = {{Halo-driven Origin and Suppression of Over-massive Black Holes and Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2026}, month = may, eid = {arXiv:2605.16485}, pages = {arXiv:2605.16485}, archiveprefix = {arXiv}, eprint = {2605.16485}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260516485S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, heavy seed, theory}, month_numeric = {5} }

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The Lumina Project: The Demographics of Active Galactic Nuclei from Quasars to Little Red Dots at z≥3

Xuejian Shen, Oliver Zier, Aaron Smith, and 16 more authors

arXiv e-prints, May 2026

Abs ADS arXiv

High-redshift active galactic nuclei (AGN) serve as powerful probes of early black-hole growth, galaxy formation, and the evolving intergalactic medium (IGM). In this work, we use Lumina, a cosmological radiation-hydrodynamic simulation spanning the epochs of hydrogen and helium reionization, which combines a large (500\,\rm cMpc)^3 volume with 2\times 6000^3 resolution elements, to explore high-redshift AGN. The simulation self-consistently follows hundreds of millions of galaxies and supermassive black holes (SMBHs), together with their impact on the ionization and thermal state of the IGM. We exploit this uniquely large dynamic range to predict multi-band AGN luminosity functions (LFs) at z ≥3, from hard X-rays to the mid-infrared. These predictions encompass both moderately luminous quasars and the faint “Little Red Dots” (LRDs) uncovered by JWST. We develop an empirical model that maps simulated SMBHs onto observed AGN using bolometric and extinction/absorption corrections for canonical AGN and LRDs, and in which SMBHs with M_\rm BH≤10 M_\rm seed ∼10^7\,\rm M_⊙ stay in the LRD phase with a duty cycle of 30%. This simple framework reproduces the observed LFs and clustering of LRDs. Meanwhile, the pre-JWST quasar LF constraints are recovered, although we find that a ∼0.3 dex log-normal scatter in bolometric luminosity is required to reproduce the bright end. We place the simulated AGN population in the cosmological context by quantifying the redshift evolution of AGN and LRD number densities, and their contributions to the integrated BH mass densities. The same AGN population is the dominant driver for the HeII reionization modelled self-consistently in Lumina. This empirical AGN model paves the way for general population-synthesis models of high- redshift AGN, including LRDs, in a unified cosmological framework.

@article{2026arXiv260524112S, author = {{Shen}, Xuejian and {Zier}, Oliver and {Smith}, Aaron and {Liu}, Rongrong and {Kannan}, Rahul and {Bulichi}, Teodora-Elena and {Koehler}, Sonja M. and {Springel}, Volker and {Vogelsberger}, Mark and {Hernquist}, Lars and {Naidu}, Rohan P. and {de Graaff}, Anna and {Pizzati}, Elia and {Alexander}, David M. and {Ho}, Luis C. and {Kokorev}, Vasily and {Leung}, Gene and {Eilers}, Anna-Christina and {Hickox}, Ryan C.}, title = {{The Lumina Project: The Demographics of Active Galactic Nuclei from Quasars to Little Red Dots at $z\geq 3$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2026}, month = may, eid = {arXiv:2605.24112}, pages = {arXiv:2605.24112}, archiveprefix = {arXiv}, eprint = {2605.24112}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260524112S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, agn-dominated, clustering, early universe, simulation}, month_numeric = {5} }

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On the quenching of LRD X-ray emission by both Compton-thick gas and high accretion rates

Albert Sneppen, Darach Watson, James H. Matthews, and 1 more author

arXiv e-prints, May 2026

Abs ADS arXiv

Little Red Dots (LRDs), candidate high-redshift supermassive black holes accreting in dense gas, remain undetected in X-rays. In previous work, we provided the first quantitative models that reproduce the optical and near-infrared spectra of LRDs with the Sirocco radiative transfer code, thereby constraining the properties of the surrounding gas. Here, we use those constraints to predict the X-ray attenuation produced by dense gas cocoons, and explore its dependence on Balmer-break strength, metallicity, intrinsic X-ray SED, and observed bandpass as a function of redshift. We find that the X-ray constraints are very tight, requiring both extinction by a Compton-thick gas column N_\rm H\sim10^25\,\rm cm^-2 with moderate metallicity (0.05-0.1 Z_⊙) and intrinsically weak X-ray emission (bolometric to X-ray luminosity ratio, k_\rm bol,Xrsim 30) as observed in high accretion rate, narrow-line AGN, to make LRDs sufficiently faint to evade detection. Intrinsically bright X-ray emitters as seen in typical broad-line AGN would be detected even behind the typical modest metallicity, Compton- thick gas columns inferred from the optical spectra. Very low metallicity objects could be detected in X-rays even with low intrinsic X-ray luminosities, suggesting that LRDs are not (currently) chemically pristine.

@article{2026arXiv260515263S, author = {{Sneppen}, Albert and {Watson}, Darach and {Matthews}, James H. and {Sim}, Stuart A.}, title = {{On the quenching of LRD X-ray emission by both Compton-thick gas and high accretion rates}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = may, eid = {arXiv:2605.15263}, pages = {arXiv:2605.15263}, archiveprefix = {arXiv}, eprint = {2605.15263}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260515263S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, obscuration, simulation, super-eddington, x-ray}, month_numeric = {5} }

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Little Red Dot \ensuremath- Host Galaxy = Black Hole Star: A Gas-Enshrouded Heart at the Center of Every Little Red Dot

Wendy Q. Sun, Rohan P. Naidu, Jorryt Matthee, and 30 more authors

The Open Journal of Astrophysics, May 2026

Abs DOI ADS arXiv

The central engines of Little Red Dots (LRDs) may be “black hole stars” (BH*s), early stages of black hole growth characterized by dense gas envelopes. So far, the most direct evidence for BH*s comes from a handful of sources where the host galaxy is completely outshone as suggested by their remarkably steep Balmer breaks. Here we present a novel scheme to disentangle BH*s from their host galaxies assuming that the [OIII]5008Å line arises exclusively from the host. Using a sample of 98 LRDs ( z≍2\ensuremath-9) with high quality NIRSpec/PRISM spectra, we demonstrate that the host-subtracted median stack displays a Balmer break >2\texttimes stronger than massive quiescent galaxies, with the rest-optical continuum resembling a blackbody-like SED ( K, erg s, au). We measure a steep Balmer decrement (H \ensuremathα/H \ensuremathβ>10) and numerous density-sensitive features (e.g., FeII, HeI, OI). These are hallmark signatures of dense gas envelopes, providing population-level evidence that BH*s indeed power LRDs. In the median LRD, BH*s account for \ensuremath∼20% of the UV emission, \ensuremath∼50% at the Balmer break, and \ensuremath∼90% at wavelengths longer than H \ensuremathα with the remainder arising from the host. BH*s preferentially reside in low-mass galaxies () undergoing recent starbursts, as evidenced by extreme emission line EWs (e.g., [OIII]5008Å ≍1100Å, CIII] ≍12Å), thereby favoring BH* origins linked to star-formation. We show V-shaped LRD selections are biased to high BH*/host fractions ( \ensuremath≳60% at 5500Å) ─ less dominant BH*s may be powering JWST’s blue broad-line AGN. We find BH*s are so commonplace and transient (duty cycle \ensuremath∼1%, lifetime \ensuremath∼10 Myrs) that every massive black hole may have once shone as a BH*.

@article{2026OJAp....962505S, author = {{Sun}, Wendy Q. and {Naidu}, Rohan P. and {Matthee}, Jorryt and {de Graaff}, Anna and {Chisholm}, John and {Greene}, Jenny E. and {Oesch}, Pascal A. and {Torralba}, Alberto and {Hviding}, Raphael E. and {Brammer}, Gabriel and {Simcoe}, Robert A. and {Bose}, Sownak and {Bouwens}, Rychard and {Dayal}, Pratika and {Eilers}, Anna-Christina and {Fei}, Qinyue and {Furtak}, Lukas J. and {Gottumukkala}, Rashmi and {Goulding}, Andy and {Heintz}, Kasper E. and {Hirschmann}, Michaela and {Kokorev}, Vasily and {Leja}, Joel and {Liu}, Zhaoran and {Natarajan}, Priyamvada and {Santarelli}, Andrew D. and {Setton}, David J. and {Smith}, Aaron and {Tacchella}, Sandro and {Volonteri}, Marta and {Walter}, Fabian and {Weibel}, Andrea and {Williams}, Christina C.}, title = {{Little Red Dot {\ensuremath{-}} Host Galaxy = Black Hole Star: A Gas-Enshrouded Heart at the Center of Every Little Red Dot}}, journal = {The Open Journal of Astrophysics}, year = {2026}, month = may, volume = {9}, pages = {62505}, doi = {10.33232/001c.162505}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026OJAp....962505S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2601.20929}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {composite, host galaxy, jwst, sed, spectroscopy}, month_numeric = {5} }

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Transient Signatures of Star-Envelope Collisions in Little Red Dots

Tomoya Suzuguchi and Kohei Inayoshi

arXiv e-prints, May 2026

Abs DOI ADS arXiv

Little red dots (LRDs) are compact high-redshift objects, newly discovered by the James Webb Space Telescope. Although LRDs exhibit broad Balmer emission lines suggestive of the presence of active galactic nuclei (AGN), their spectral features differ significantly from those of ordinary AGN. Recent studies suggest that their characteristics can be explained if accreting supermassive black holes (SMBHs) are embedded within dense gaseous envelopes and surrounded by compact stellar clusters. In this scenario, stars in the cluster can scatter onto plunging orbits that intersect the envelope and collide with its surface. Here we investigate the observational properties of such star- envelope collisions as luminous transient events. We find that collisions involving red supergiants with radii of ∼10^3~R_⊙, together with gaseous envelopes whose masses are comparable to those of the central SMBHs, are the most promising targets due to their high luminosities and long durations. For compact clusters with sizes of ≲10~\rm pc, such massive stars can participate in star-envelope collisions within their lifetimes at event rates reaching ∼0.3~\rm yr^-1 per LRD. We show that these transients are detectable with future wide-field surveys such as the Nancy Grace Roman Space Telescope if they occur at relatively low redshifts (z ≲1). Detection of such transients would provide strong evidence for the envelope+stellar-cluster scenario of LRDs and offer a unique probe of the envelope mass, which is otherwise difficult to constrain from LRD spectra alone.

@article{2026arXiv260529895S, author = {{Suzuguchi}, Tomoya and {Inayoshi}, Kohei}, title = {{Transient Signatures of Star-Envelope Collisions in Little Red Dots}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.29895}, pages = {arXiv:2605.29895}, doi = {10.48550/arXiv.2605.29895}, archiveprefix = {arXiv}, eprint = {2605.29895}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260529895S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, theory, variability}, month_numeric = {5} }

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A Magnetized Black Hole Envelope Model for Little Red Dots

Shinsuke Takasao and Kohei Inayoshi

arXiv e-prints, May 2026

Abs DOI ADS arXiv

Recent observations have revealed a unique class of active galactic nuclei (AGNs), termed little red dots (LRDs). These objects are hypothesized to be powered by massive black holes rapidly accreting in dense gaseous environments. Theoretical studies suggest that the circum-nuclear gas can form an optically thick black hole envelope (BHE), whose structure resembles the atmospheres of convective stars near the Hayashi limit. Given that such cool stars typically generate magnetic fields, we propose a dynamical and spectral model for an LRD enshrouded by a magnetized BHE. Assuming spherical free-fall accretion onto a rotating, magnetized BHE, our model accounts for key observational properties of LRDs. We propose that the Doppler component of broad emission lines originates from plasma clumps co-rotating within the BHE magnetosphere. Including additional broadening due to electron scattering allows the resulting line profile to be fitted by a combination of a Gaussian core and an exponential tail. This model can reproduce Doppler components up to a few thousand \rm km~s^-1. We suggest that conventional black hole mass estimation methods based on the virial relation may yield erroneous results. Furthermore, our model is consistent with X-ray non-detections in LRDs. We evaluate the X-ray luminosities of two potential sources: the post-shock region of accretion shocks and a magnetically heated corona. We find that these X-ray luminosities are constrained to ≲10^41~\rm erg~s^-1 across a wide range of black hole masses (10^5 M_⊙≲M_\rm BH≲10^7M_⊙) and accretion rates, consistent with current upper limits on X-ray emission.

@article{2026arXiv260521589T, author = {{Takasao}, Shinsuke and {Inayoshi}, Kohei}, title = {{A Magnetized Black Hole Envelope Model for Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics}, year = {2026}, month = may, eid = {arXiv:2605.21589}, pages = {arXiv:2605.21589}, doi = {10.48550/arXiv.2605.21589}, archiveprefix = {arXiv}, eprint = {2605.21589}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260521589T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, theory, x-ray}, month_numeric = {5} }

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DREAMS. JWST Spectroscopy of a z=8.3 Galaxy with an ALMA Dust Continuum Detection: Early Dust, Very High T_\rm dust, and a Multi-wavelength [OIII] Ratio Discrepancy

Kana Takechi, Masami Ouchi, Kimihiko Nakajima, and 10 more authors

arXiv e-prints, May 2026

Abs ADS arXiv

We present a deep DREAMS JWST/NIRSpec MSA medium-grating spectrum of MACS0416-Y1, a galaxy at z=8.312 with the highest-redshift ALMA dust continuum detection to date, in order to characterize its properties together with archival IFU and ALMA data. The deep NIRSpec spectrum reveals a broad Hβ line with a width of \sim1100 km s^-1. We interpret it as a broad-line AGN whose line diagnostics are consistent with AGN activity across its clumpy structure, given the absence of little red dot signatures. MACS0416-Y1 clearly shows [OIII]4363 emission, suggesting a moderately low metallicity of 12+\log(\mathrmO/H)=7.86^+0.09_-0.08 (0.15~Z_⊙). The combination of [CII]158μm and dust continuum emission indicates low dust mass ratios of \log (M_\rm dust/M_\rm gas)=-3.60^+0.29_-0.22 and \log (M_\rm dust/M_\rm metal)=-0.95^+0.29_-0.20. Because the metallicity of MACS0416-Y1 is around the critical metallicity of 0.1\textrm-0.2~Z_⊙, the system is expected to undergo dust growth, explaining these low dust mass ratios as well as its small dust mass, M_\rm dust\sim10^6~M_⊙. The intense UV radiation from the AGN may contribute to a high dust temperature of T_\rm dust≃91^+62_-35 K, boosting the dust-continuum emission above the ALMA detection limit despite the small M_\rm dust at z>8. We find a very high total flux ratio of [OIII]88μm/[OIII]5007 = 0.26 \pm 0.06 in MACS0416-Y1, above predictions from single ionized nebular models at any electron density. This discrepancy suggests that the [OIII]88μm and [OIII]5007 trace largely distinct regions, with the optical line suppressed in dusty nebulae, and thus requires careful interpretation when combining optical and infrared emission lines in JWST+ALMA studies.

@article{2026arXiv260514922T, author = {{Takechi}, Kana and {Ouchi}, Masami and {Nakajima}, Kimihiko and {Kiyota}, Tomokazu and {Tamura}, Yoichi and {Harikane}, Yuichi and {Nakazato}, Yurina and {Bakx}, Tom J. L. C. and {Inoue}, Akio K. and {Yajima}, Hidenobu and {Hagimoto}, Masato and {Ono}, Yoshiaki and {Xu}, Yi}, title = {{DREAMS. JWST Spectroscopy of a $z=8.3$ Galaxy with an ALMA Dust Continuum Detection: Early Dust, Very High $T\_{\rm dust}$, and a Multi-wavelength [OIII] Ratio Discrepancy}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = may, eid = {arXiv:2605.14922}, pages = {arXiv:2605.14922}, archiveprefix = {arXiv}, eprint = {2605.14922}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260514922T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, alma, emission lines, jwst, multi-wavelength}, month_numeric = {5} }

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The Missing Hard Photons of Little Red Dots: Their Incident Ionizing Spectra Resemble Massive Stars

Bingjie Wang, Joel Leja, Harley Katz, and 11 more authors

The Astrophysical Journal, May 2026

Abs DOI ADS arXiv

The nature of little red dots (LRDs) has largely been investigated through their continuum emission, with lines assumed to arise from a broad-line region. In this paper, we instead use recombination lines to infer the intrinsic properties of the central engine. Our analysis first reveals a tension between the ionizing properties implied from H\ensuremathα and He II \ensuremathλ4686. The high H\ensuremathα EWs require copious H-ionizing photons, more than the bluest active galactic nucleus (AGN) ionizing spectra can provide. In contrast, He II emission is marginally detected, and its low EW is, at most, consistent with the softest AGN spectra. The low He II/H\ensuremathβ (\ensuremath∼10^\ensuremath-2, 10) from gas/dust, and soft ionizing spectra with abundant H-ionizing photons, consistent with, e.g., a cold accretion disk or a composite of AGN and stars. The latter is an intriguing scenario since high hydrogen densities are highly conducive for star formation, and nuclear star clusters are found in the vicinity of local massive black holes. While previous studies have mostly focused on features dominated by the absorbing hydrogen cloud, the He II-based diagnostic proposed here represents a crucial step toward understanding the central engine of LRDs.

@article{2026ApJ..1003...10W, author = {{Wang}, Bingjie and {Leja}, Joel and {Katz}, Harley and {Inayoshi}, Kohei and {Cleri}, Nikko J. and {de Graaff}, Anna and {Hviding}, Raphael E. and {van Dokkum}, Pieter and {Greene}, Jenny E. and {Labb{\'e}}, Ivo and {Matthee}, Jorryt and {McConachie}, Ian and {Naidu}, Rohan P. and {Nelson}, Erica J.}, title = {{The Missing Hard Photons of Little Red Dots: Their Incident Ionizing Spectra Resemble Massive Stars}}, journal = {\apj}, keywords = {Active galactic nuclei, Galaxy formation, Photoionization, Spectral energy distribution, 16, 595, 2060, 2129, Astrophysics of Galaxies}, year = {2026}, month = may, volume = {1003}, number = {1}, eid = {10}, pages = {10}, doi = {10.3847/1538-4357/ae5bab}, archiveprefix = {arXiv}, eprint = {2508.18358}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1003...10W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, emission lines, exotic physics, simulation, theory}, month_numeric = {5} }

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Little red dots challenge theory

Paul Woods

Nature Astronomy, May 2026

DOI ADS

@article{2026NatAs..10..600W, author = {{Woods}, Paul}, title = {{Little red dots challenge theory}}, journal = {Nature Astronomy}, year = {2026}, month = may, volume = {10}, pages = {600-600}, doi = {10.1038/s41550-026-02879-6}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026NatAs..10..600W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, heavy seed, jwst, theory}, month_numeric = {5} }

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Born in the Dark: The Catastrophic Collapse of Fuzzy Dark Matter Solitons as the Origin of Little Red Dots

Tak-Pong Woo

The Astrophysical Journal, May 2026

Abs DOI ADS

JWST surveys have uncovered a population of compact, red sources (“Little Red Dots,” LRDs) at z \ensuremath≥ 5 that exhibit broad Balmer emission yet remain X-ray faint, implying heavy obscuration with N_H \ensuremath≥ 10^24 cm^\ensuremath-2. We propose that LRDs trace a short- lived, obscured phase associated with rapid baryonic inflow inside the deep solitonic cores of fuzzy dark matter halos. Combining the soliton size scaling with the observed compact radii (r_e \ensuremath∼ 30─100 pc), we find that while a particle mass of m \ensuremath∼ 2 \texttimes 10^\ensuremath-22 eV provides a direct match for mature systems, the observed size─mass relation is fully consistent with heavier bosons (m_22 \ensuremath≳ 20, satisfying Ly\ensuremathα constraints) if LRDs represent a progenitor phase where the central black hole is still growing (M_BH < M_c). We adopt m_22 = 2 as a fiducial baseline to demonstrate the thermodynamic instability. A conservative mass-budget estimate indicates that configurations reaching N_H \ensuremath≥ 10^24─10^25 cm^\ensuremath-2 require densities for which radiative losses (cooling and/or diffusion) occur faster than the dynamical time, suggesting that a long- lived static hot atmosphere is unlikely (an “Opacity Crisis”) and that rapid inflow or radiation-pressure-driven evolution is favored. Using 512^3 pseudospectral Schrödinger─Poisson simulations of idealized soliton mergers, we illustrate that compact, high-density soliton cores form robustly under representative scalings. We discuss observational implications and tests and outline the need for future radiation-hydrodynamic modeling to predict demographics and detailed spectra.

@article{2026ApJ..1002...41W, author = {{Woo}, Tak-Pong}, title = {{Born in the Dark: The Catastrophic Collapse of Fuzzy Dark Matter Solitons as the Origin of Little Red Dots}}, journal = {\apj}, keywords = {Supermassive black holes, High-redshift galaxies, Dark matter, Quasars, Early universe, 1663, 734, 353, 1319, 435}, year = {2026}, month = may, volume = {1002}, number = {1}, eid = {41}, pages = {41}, doi = {10.3847/1538-4357/ae5230}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1002...41W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, exotic physics, obscuration, simulation, theory}, month_numeric = {5} }

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Balmer Transition Signatures from Gas-enshrouded, Dust-poor Active Galactic Nuclei

Zu Yan, Kohei Inayoshi, Kejian Chen, and 1 more author

The Astrophysical Journal, May 2026

Abs DOI ADS arXiv

Little red dots (LRDs), a population of active galactic nuclei (AGNs) recently discovered by JWST, show distinctive Balmer-transition features, including prominent Balmer absorption, pronounced Balmer breaks, and large equivalent widths of broad H\ensuremathα emission, all of which indicate the presence of dense gas surrounding their central black holes. A further key property of LRDs is their large Balmer decrements with broad H\ensuremathα/H\ensuremathβ line- flux ratios far exceeding the Case B recombination value. These ratios of H\ensuremathα/H\ensuremathβ > 3 have often been interpreted as evidence for heavy dust extinction (A_V \ensuremath≳ 3 mag); however, such dust would inevitably produce strong near-to-mid infrared reemission that is hardly seen in JWST/MIRI observations. To investigate the physical origin of these observed Balmer features, we perform radiation transfer calculations through dust-free, dense gas. We show that the observed large Balmer decrements (H\ensuremathα/H\ensuremathβ and H\ensuremathα/H\ensuremathγ) naturally arise from Balmer resonance scattering without invoking dust. At sufficiently high densities (n_H \ensuremath≳ 10^8\ensuremath-9 cm^\ensuremath-3), the elevated multiple Balmer-line ratios converge to values that closely mimic dust reddening, explaining why LRD spectra resemble obscured AGNs. Furthermore, when the Balmer break and broad Balmer lines originate in the same dense gas, their strengths are physically linked, allowing us to constrain the density structure and infer a low broad-line region gas mass of \ensuremath∼O(10M\ensuremath⊙). Such a small gas reservoir would be enriched by even a single supernova, implying that LRDs with observed low-metallicity signatures likely experienced minimal star formation in their nuclei.

@article{2026ApJ..1002..159Y, author = {{Yan}, Zu and {Inayoshi}, Kohei and {Chen}, Kejian and {Guo}, Jingsong}, title = {{Balmer Transition Signatures from Gas-enshrouded, Dust-poor Active Galactic Nuclei}}, journal = {\apj}, keywords = {Supermassive black holes, High-redshift galaxies, Quasars, Interstellar medium, 1663, 734, 1319, 847, Astrophysics of Galaxies}, year = {2026}, month = may, volume = {1002}, number = {2}, eid = {159}, pages = {159}, doi = {10.3847/1538-4357/ae5dbd}, archiveprefix = {arXiv}, eprint = {2512.11050}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1002..159Y}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, emission lines, obscuration, simulation}, month_numeric = {5} }

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The composite spectrum of little red dots from a standard inner disk and an unstable outer disk

Chenxuan Zhang, Qingwen Wu, Xiao Fan, and 6 more authors

Nature Astronomy, May 2026

Abs DOI ADS arXiv

The James Webb Space Telescope has revealed a new class of high- redshift, very red, compact broad-line sources, termed ‘little red dots’ (LRDs). The physical mechanism driving these properties remains elusive. Here we construct spectral energy distributions with a spectroscopic redshift for 28 LRDs, finding that they have V-shaped SEDs with a common break frequency of \ensuremathν_b \ensuremath≈ 10^14.96\ensuremath\pm0.06 Hz. We propose that these unique SEDs can be explained well by the combination of an inner standard disk and an outer gravitationally unstable accretion disk with Toomre parameter Q \ensuremath≈ 1. The outer disk has a temperature of \raisebox-0.5ex\textasciitilde2,000-4,000 K and mainly radiates in near-infrared-to-optical wavebands. The composite spectrum from this model naturally explains the V-shaped continuum and reproduces the intrinsically luminous infrared-to- optical emission without requiring extreme dust extinction or unusual stellar populations. Even when we considered possible dense gas around the disk to account for pronounced Balmer breaks in some LRDs, the intrinsic optical-to-ultraviolet emission is suppressed by factors of only \ensuremath≲2-3, which indicates that most LRDs are sub-Eddington and intrinsically weak. These results provide new insights into early-phase black hole growth and galaxy evolution.

@article{2026NatAs..10..753Z, author = {{Zhang}, Chenxuan and {Wu}, Qingwen and {Fan}, Xiao and {Ho}, Luis C. and {Wu}, Jiancheng and {Zhang}, Huanian and {Lyu}, Bing and {Cao}, Xinwu and {Wang}, Jianmin}, title = {{The composite spectrum of little red dots from a standard inner disk and an unstable outer disk}}, journal = {Nature Astronomy}, keywords = {High Energy Astrophysical Phenomena}, year = {2026}, month = may, volume = {10}, pages = {753-761}, doi = {10.1038/s41550-026-02785-x}, archiveprefix = {arXiv}, eprint = {2505.12719}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026NatAs..10..753Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, sed, theory}, month_numeric = {5} }

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Little Red Dots as Self-gravitating Disks Accreting on Supermassive Stars: Spectral Appearance and Formation Pathway of the Progenitors to Direct Collapse Black Holes

Lorenz Zwick, Christopher Tiede, and Lucio Mayer

The Astrophysical Journal, May 2026

Abs DOI ADS arXiv

We propose an alternative physical interpretation and formation pathway for the recently discovered “little red dots” (LRDs). We model LRDs as supermassive stars (SMSs) surrounded by massive self- gravitating accretion disks (supermassive disks, SMDs) that form as a consequence of gas-rich major galaxy mergers. The model provides an excellent match for numerous spectral features of LRDs, where the V-shape arises from the superposition of two black bodies, and Balmer line broadening is sourced by the intrinsic rotation of the SMD. No additional active galactic nucleus, stellar, dust, or broadening component is strictly required. This results in a model with physically motivated parameters that are robust to variations in observed LRD properties. We perform Markov Chain Monte Carlo fits for two representative LRD spectra, for which the full parameter posterior distributions are determined. Allowing for a compressed SMS mass─radius relation, the recovered parameters are compatible with sub-Eddington accretion in self-gravitating disks, and the recovered SMS masses of few 10^6 M_\ensuremath⊙ imply the subsequent formation of massive black holes (BHs) that squarely follow the expected BH mass─galaxy mass relation, while also predicting a cutoff luminosity of the order of few 10^44 erg s^\ensuremath-1 in quantitative agreement with current observations. While matching the abundance of LRDs is challenging, the association to galaxy mergers produces a redshift distribution that reflects observations.

@article{2026ApJ..1002....7Z, author = {{Zwick}, Lorenz and {Tiede}, Christopher and {Mayer}, Lucio}, title = {{Little Red Dots as Self-gravitating Disks Accreting on Supermassive Stars: Spectral Appearance and Formation Pathway of the Progenitors to Direct Collapse Black Holes}}, journal = {\apj}, keywords = {Active galaxies, Galaxy mergers, Astrophysical black holes, James Webb Space Telescope, Quasars, 17, 608, 98, 2291, 1319}, year = {2026}, month = may, volume = {1002}, number = {1}, eid = {7}, pages = {7}, doi = {10.3847/1538-4357/ae4d47}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1002....7Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {exotic physics, heavy seed, non-agn, sed, theory}, eprint = {2507.22014}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {5} }

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Dark matter in galactic structure: From the milky way to the high redshift universe

C. R. Argüelles, E. A. Becerra-Vergara, S. Collazo, and 8 more authors

International Journal of Modern Physics D, Apr 2026

Abs DOI ADS

Different cosmological models relying upon different dark matter (DM) particle candidates such as WIMPS, sterile neutrinos or axions, can provide a successful enough description of the large scale structure of the Universe. However, important open questions remain to be answered on galaxy scales. They include how to robustly infer and predict the inner/outer slope of the DM profiles; how DM concentrates towards galaxy centers, or which is the nature of the relation between supermassive black holes (SMBHs) and their hosting halos. Another unresolved and seemingly unrelated problem in cosmology has to do with the nature, seed and growth of the SMBHs in the high redshift Universe. Remarkably, by assuming the DM halos are made of neutral fermions held together by gravity, it is possible to obtain key insights to all of the above questions. We present here a brief overview on fermionic DM highlighting on several applications developed in the last decade, as discussed at the 17th Marcel Grossmann Meeting (MG17). Special attention is given to galaxy scales, the Milky Way’s center (nature of SgrA*) and the outer halo shape, as well as the role of the fermionic DM particle on early galaxy formation. The presented results make emphasis on different predictions of the model together with an explicit connection to observational data including astrometric measurements of the S2-orbit, recent EHT images of Sagittarius A* (Sgr A*), GAIA DR3 rotation curve of the Milky Way, and JWST data from the most distant galaxies and little red dots.

@article{2026IJMPD..3540018A, author = {{Arg{\"u}elles}, C. R. and {Becerra-Vergara}, E. A. and {Collazo}, S. and {Crespi}, V. and {Deluca}, A. and {Krut}, A. and {Mestre}, M. F. and {Pelle}, J. and {Rueda}, J. A. and {Ruffini}, R. and {Vieyro}, F. L.}, title = {{Dark matter in galactic structure: From the milky way to the high redshift universe}}, journal = {International Journal of Modern Physics D}, keywords = {Dark matter, galaxies: super massive black holes {\textemdash} halos, self-gravitating systems: fermions}, year = {2026}, month = apr, volume = {35}, number = {6}, eid = {2540018}, pages = {2540018}, doi = {10.1142/S0218271825400188}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026IJMPD..3540018A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, exotic physics, jwst, theory}, month_numeric = {4} }

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Gas accretion versus black-hole-merger-driven growth modes of supermassive black holes and implications for the little red dots

Paramita Barai

Astronomy & Astrophysics, Apr 2026

Abs DOI ADS arXiv

We investigated the growth of central supermassive black holes (SMBHs) in galaxies, with the aim of distinguishing between gas accretion and black-hole (BH) merger-driven growth modes. We performed cosmological hydrodynamical simulations of (50 Mpc)^3 comoving volumes, and analyzed how the BH feedback parameters affect the coevolution between SMBHs and their host galaxies. Starting as 10^5 M_\ensuremath⊙ seeds, we find that the BHs initially grow via BH mergers to \ensuremath∼10^7 M_\ensuremath⊙. Gas accretion onto the BHs is low soon after seeding, and then the accretion rate increases with time and reaches the Eddington rate after 7 \ensuremath- 9 Gyr. The BHs then undergo very fast growth via efficient gas accretion over a time period of 600 \ensuremath- 700 Myr; during this period the BH mass increases 10^2 \ensuremath- 10^3 times, causing their predominant growth from 10^7 M_\ensuremath⊙ to (10^9 \ensuremath- 10^10) M_\ensuremath⊙. Taking into account the cosmological gas inflows and outflows, SMBHs do not grow to more than 10^10 M_\ensuremath⊙ by z = 0, which is because of gas depletion from galaxy centers driven by BH feedback. In terms of the coevolution of SMBHs and their host galaxies along the M_BH \ensuremath- M_★ relation, we find that they initially lie below the relation at earlier epochs and thereby move upward toward the relation. We made some physical implications about the growth of high-z little red dots recently observed by the JWST: the normal-mass SMBHs had predominantly undergone BH-merger-driven evolution, whereas the overmassive BHs underwent periods of Eddington-limited or super- Eddington bursts of gas accretion.

@article{2026A&A...709A...9B, author = {{Barai}, Paramita}, title = {{Gas accretion versus black-hole-merger-driven growth modes of supermassive black holes and implications for the little red dots}}, journal = {\aap}, keywords = {black hole physics, hydrodynamics, methods: numerical, galaxies: formation, quasars: supermassive black holes, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2026}, month = apr, volume = {709}, eid = {A9}, pages = {A9}, doi = {10.1051/0004-6361/202558028}, archiveprefix = {arXiv}, eprint = {2602.15952}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...709A...9B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, heavy seed, simulation, super-eddington, theory}, month_numeric = {4} }

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Do little red dots really form a distinct class of astronomical objects?

Jean-Baptiste Billand, David Elbaz, Maximilien Franco, and 8 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

JWST observations have identified a class of enigmatic sources known as “Little Red Dots” (LRDs). These have been interpreted as a distinct class of active galactic nuclei (AGN) and host galaxies, potentially involving “quasi-stars” or Black Hole stars (BH*). However, two questions remain: is there a clear discontinuity between LRDs and field galaxies, and do LRDs form a homogeneous population? In this work, we address these issues by introducing a continuous metric to evaluate the “LRDness” of galaxies. We measure their compactness (δ_compact), the sharpness of the V-shaped spectral energy distribution (δ_v-shape), and the strength of the broad Balmer line emission. We apply this approach to a sample of \raisebox-0.5ex\textasciitilde48,000 galaxies with photometric and \raisebox-0.5ex\textasciitilde5,000 with spectroscopic information, selected over \raisebox-0.5ex\textasciitilde750 arcmin\^2. We find that V-shape prominence correlates strongly with morphology without a clear transition at common LRD selection thresholds: the fraction of compact galaxies rises continuously with V-shape intensity. Similarly, broad Hα strength increases with both V-shape sharpness and compactness. The [N II] deficit is not an exclusive feature of LRDs but a global property of compact, metal-poor galaxies. Only the 3% most extreme LRDs present a prominent Balmer break (>3) of potentially non-stellar origin. LRDs and non-LRDs follow similar trends in the evolution of the Balmer decrement with V-shape sharpness, suggesting a shared physical origin, likely dust attenuation. Estimated dust masses (\raisebox-0.5ex\textasciitilde4-7 x 10\^4 M_{sun}) and luminosities are low enough to account for their non-detection by ALMA. We conclude that most LRDs do not represent a separate class of objects, but rather the extreme tail of a continuous distribution of galaxies and broad Hα emitters, consistent with a classical broad line region and dust attenuation.

@article{2026arXiv260411677B, author = {{Billand}, Jean-Baptiste and {Elbaz}, David and {Franco}, Maximilien and {Gentile}, Fabrizio and {Daddi}, Emanuele and {Giavalisco}, Mauro and {Kocevski}, Dale D. and {Lewis}, Joseph S. W. and {Magnelli}, Benjamin and {Sangalli}, Valentina and {Tarrasse}, Maxime}, title = {{Do little red dots really form a distinct class of astronomical objects?}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.11677}, pages = {arXiv:2604.11677}, archiveprefix = {arXiv}, eprint = {2604.11677}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260411677B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, morphology, obscuration, sed, spectroscopy}, month_numeric = {4} }

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Classifying Supermassive Black Hole Growth Regimes to Observables Across Cosmological Simulations with Forecasts for LSST

Hitaishi Chillara

arXiv e-prints, Apr 2026

Abs ADS arXiv

The possibility of over-massive black holes suggested by James Webb Space Telescope photometric discoveries of ’little red dots’, may disfavor light supermassive black hole (SMBH) seeds. However, what should constitute the mass (range) of ’heavy’ seeds remains relatively unconstrained. Moreover, Vera C Rubin Observatory’s Legacy Survey of Space and Time will photometrically characterize galaxies without direct black hole mass measurements. We forward-model the SIMBA, IllustrisTNG, and EAGLE cosmological simulations into the photometric bands of LSST to train an ensemble machine learning classifier. Our framework achieves 91%–94% accuracy across SIMBA and IllustrisTNG in distinguishing between over-massive and under- massive SMBH growth regimes under LSST magnitude limits, using only broadband photometry. Furthermore, cross-simulation transfer experiments (training on one cosmological simulation and evaluating on another using rank-normalized features) achieve 83%–89% accuracy. This suggests the relative photometric ordering of growth regimes is largely preserved even across fundamentally different sub-grid SMBH feedback prescriptions. Signal decomposition shows our classification is driven by host galaxy colors (82%–87% accuracy) and, relatedly, the accretion-state’s spectral energy distribution shape as opposed to an inversion of our forward model’s analytical luminosity prescription. Given that the evaluated simulations employ heavy seed prescriptions (≥10^4~M_⊙), our methodology establishes a validated baseline for classifying post-seeding growth regimes.

@article{2026arXiv260416539C, author = {{Chillara}, Hitaishi}, title = {{Classifying Supermassive Black Hole Growth Regimes to Observables Across Cosmological Simulations with Forecasts for LSST}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Instrumentation and Methods for Astrophysics}, year = {2026}, month = apr, eid = {arXiv:2604.16539}, pages = {arXiv:2604.16539}, archiveprefix = {arXiv}, eprint = {2604.16539}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260416539C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, heavy seed, photometry, sed, simulation}, month_numeric = {4} }

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BlackTHUNDER strikes twice: Balmer-line absorption in an overmassive Little Red Dot at z = 7.04

Francesco D’Eugenio, Roberto Maiolino, Michele Perna, and 29 more authors

Monthly Notices of the Royal Astronomical Society, Apr 2026

Abs DOI ADS arXiv

James Webb Space Telescope (JWST) has revealed a population of ’Little Red Dots’ (LRDs): compact, red objects at redshifts with ’v’-shaped spectral energy distributions, broad permitted lines, and, often, hydrogen Balmer absorption. We use NIRSpec/IFS data from the BlackTHUNDER survey to study the H \ensuremathα line in the LRD Abell2744-QSO1 at , which is a confirmed active galactic nucleus (AGN) due to time- variable equivalent width (EW) in its broad emission lines. The H \ensuremathα spectral profile is non-Gaussian, requiring at least two Gaussian components. We also detect a narrow-line Gaussian component, and strong H \ensuremathα absorption (EW relative to the continuum ), confirming a connection between the strong Balmer break and line absorption. The absorber is at rest with respect to broad H \ensuremathα , suggesting that the gas cannot be interpreted as an inflow or outflow, forming instead a long- lived structure. Its velocity dispersion is , consistent with the value inferred from the analysis of the Balmer break. Based on H \ensuremathα , we infer a black hole mass of , smaller but close to the previous estimates based on H \ensuremathβ . The Eddington ratio is 0.09. Combining the high signal-to-noise ratio of the narrow H \ensuremathα line with the spectral resolution of the G395H grating, we infer a narrow-line intrinsic dispersion , which places a stringent constraint on the black hole-to- dynamical mass ratio of this system to be , confirming the overmassive nature of the black hole and potentially leaving little room for a host galaxy.

@article{2026MNRAS.547ag401D, author = {{D'Eugenio}, Francesco and {Maiolino}, Roberto and {Perna}, Michele and {{\"U}bler}, Hannah and {Ji}, Xihan and {McClymont}, William and {Koudmani}, Sophie and {Sijacki}, Debora and {Juod{\v{z}}balis}, Ignas and {Scholtz}, Jan and {Bennett}, Jake S. and {Bunker}, Andrew J. and {Carniani}, Stefano and {Charlot}, St{\'e}phane and {Cresci}, Giovanni and {Curtis-Lake}, Emma and {Bont{\`a}}, Elena Dalla and {Inayoshi}, Kohei and {Jones}, Gareth C. and {Lyu}, Jianwei and {Marconi}, Alessandro and {Mazzolari}, Giovanni and {Nelson}, Erica J. and {Parlanti}, Eleonora and {Robertson}, Brant E. and {Schneider}, Raffaella and {Simmonds}, Charlotte and {Tacchella}, Sandro and {Venturi}, Giacomo and {Willott}, Chris and {Witstok}, Joris and {Witten}, Callum}, title = {{BlackTHUNDER strikes twice: Balmer-line absorption in an overmassive Little Red Dot at z = 7.04}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: high-redshift, quasars: supermassive black holes}, year = {2026}, month = apr, volume = {547}, number = {4}, eid = {stag401}, pages = {stag401}, doi = {10.1093/mnras/stag401}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.547ag401D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, black hole mass, jwst, spectroscopy}, eprint = {2503.11752}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {4} }

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Euclid: Scaled-up little red dots and other sources with v-shaped spectral energy distributions at z>4

Euclid Collaboration, A. A. Tumborang, K. I. Caputi, and 169 more authors

arXiv e-prints, Apr 2026

Abs DOI ADS arXiv

Little Red Dots (LRDs) are some the most intriguing galaxy populations recently identified at z>\raisebox-0.5ex\textasciitilde4 with JWST. They constitute the most extreme class of a more abundant population of sources with ‘V-shaped’ spectral energy distributions (SEDs) and compact morphologies, which includes also Little Blue Dots (LBDs). Finding brighter analogues to these sources requires surveying sky areas which are significantly larger than those covered with JWST. Euclid deep images are ideally suited for this purpose. We make use of Euclid near-infrared images, complemented by Spitzer Infrared Array Camera (IRAC) data, over 0.75 sq. deg. of the COSMOS field to select a sample of 233 sources with ‘V-shaped’ SEDs at z>4. Out of those, we identify 16 sources with compactness >1sigma above the median of all z>4 galaxies, which we consider robust LRD/LBD candidates in our sample. The stellar masses of these 16 sources are in the range 10\^{8.5} - 10\^{10.5} Msun, so they are significantly more massive than typical JWST-selected LRDs/LBDs. Interestingly, half of them are about as old as the Universe at their redshifts. In addition, we find that the median photometric properties of the Euclid LRDs/LBDs are similar to those of the so-called Blue Dust-Obscured Galaxies (Blue DOGs). Less than 10% of all our ‘V-shaped’ SED sources, including only one of the Euclid LBDs, correspond to known AGN. The latter mostly constitute a population disjoint to the ‘V-shaped’ SED sources. Spectroscopic follow up of the Euclid LRDs/LBD candidates remains necessary to probe whether they host BLAGN as fainter analogues do and whether constitute a transition phase from these fainter sources to standard AGN.

@article{2026arXiv260416178E, author = {{Euclid Collaboration} and {Tumborang}, A. A. and {Caputi}, K. I. and {Rinaldi}, P. and {Bisigello}, L. and {Girardi}, G. and {Iani}, E. and {Bouwens}, R. and {Navarro-Carrera}, R. and {Desprez}, G. and {Cooper}, R. A. and {Fu}, Y. and {Toba}, Y. and {Matthee}, J. and {Milvang-Jensen}, B. and {Perez-Gonzalez}, P. G. and {Ricci}, F. and {Rodighiero}, G. and {Schaye}, J. and {Tarsitano}, F. and {Zamorani}, G. and {Baes}, M. and {Gutierrez}, C. M. and {Hoekstra}, H. and {Jahnke}, K. and {Scott}, D. and {Stern}, D. and {Altieri}, B. and {Andreon}, S. and {Auricchio}, N. and {Baccigalupi}, C. and {Baldi}, M. and {Balestra}, A. and {Bardelli}, S. and {Battaglia}, P. and {Biviano}, A. and {Branchini}, E. and {Brescia}, M. and {Camera}, S. and {Capobianco}, V. and {Carbone}, C. and {Carretero}, J. and {Casas}, S. and {Castellano}, M. and {Castignani}, G. and {Cavuoti}, S. and {Chambers}, K. C. and {Cimatti}, A. and {Colodro-Conde}, C. and {Congedo}, G. and {Conselice}, C. J. and {Conversi}, L. and {Copin}, Y. and {Courbin}, F. and {Courtois}, H. M. and {Cropper}, M. and {Cuby}, J.-G. and {Da Silva}, A. and {Degaudenzi}, H. and {De Lucia}, G. and {Dole}, H. and {Douspis}, M. and {Dubath}, F. and {Dupac}, X. and {Farina}, M. and {Farinelli}, R. and {Faustini}, F. and {Ferriol}, S. and {Finelli}, F. and {Fotopoulou}, S. and {Fourmanoit}, N. and {Frailis}, M. and {Franceschi}, E. and {Fumana}, M. and {Galeotta}, S. and {George}, K. and {Gillis}, B. and {Giocoli}, C. and {Gracia-Carpio}, J. and {Grazian}, A. and {Grupp}, F. and {Haugan}, S. V. H. and {Holmes}, W. and {Hook}, I. M. and {Hormuth}, F. and {Hornstrup}, A. and {Jhabvala}, M. and {Joachimi}, B. and {Kermiche}, S. and {Kiessling}, A. and {Kubik}, B. and {K{\"u}mmel}, M. and {Kunz}, M. and {Kurki-Suonio}, H. and {Le Brun}, A. M. C. and {Ligori}, S. and {Lilje}, P. B. and {Lindholm}, V. and {Lloro}, I. and {Mainetti}, G. and {Maiorano}, E. and {Mansutti}, O. and {Marcin}, S. and {Marggraf}, O. and {Martinelli}, M. and {Martinet}, N. and {Marulli}, F. and {Massey}, R. J. and {Medinaceli}, E. and {Mei}, S. and {Meneghetti}, M. and {Merlin}, E. and {Meylan}, G. and {Mora}, A. and {Moresco}, M. and {Moscardini}, L. and {Neissner}, C. and {Nichol}, R. C. and {Niemi}, S.-M. and {Nightingale}, J. W. and {Padilla}, C. and {Paltani}, S. and {Pasian}, F. and {Pedersen}, K. and {Percival}, W. J. and {Pettorino}, V. and {Pires}, S. and {Polenta}, G. and {Poncet}, M. and {Popa}, L. A. and {Pozzetti}, L. and {Raison}, F. and {Renzi}, A. and {Rhodes}, J. and {Riccio}, G. and {Romelli}, E. and {Roncarelli}, M. and {Rusholme}, B. and {Saglia}, R. and {Sakr}, Z. and {Sapone}, D. and {Schirmer}, M. and {Schneider}, P. and {Schrabback}, T. and {Secroun}, A. and {Seidel}, G. and {Sihvola}, E. and {Simon}, P. and {Sirignano}, C. and {Sirri}, G. and {Stanco}, L. and {Tallada-Cresp{\'\i}}, P. and {Taylor}, A. N. and {Teplitz}, H. I. and {Tereno}, I. and {Tessore}, N. and {Toft}, S. and {Toledo-Moreo}, R. and {Torradeflot}, F. and {Tutusaus}, I. and {Valenziano}, L. and {Valiviita}, J. and {Vassallo}, T. and {Verdoes Kleijn}, G. and {Veropalumbo}, A. and {Wang}, Y. and {Weller}, J. and {Zerbi}, F. M. and {Zucca}, E. and {Huertas-Company}, M. and {Mart{\'\i}n-Fleitas}, J. and {Scottez}, V.}, title = {{Euclid: Scaled-up little red dots and other sources with v-shaped spectral energy distributions at z>4}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.16178}, pages = {arXiv:2604.16178}, doi = {10.48550/arXiv.2604.16178}, archiveprefix = {arXiv}, eprint = {2604.16178}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260416178E}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, morphology, non-jwst, photometry, sed}, month_numeric = {4} }

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Supermassive Primordial Black Holes from a Catalyzed Dark Phase Transition for Little Red Dots

Jinhui Guo, Jia Liu, Masanori Tanaka, and 2 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

JWST has revealed an abundant population of compact, low-metallicity “Little Red Dots” (LRDs) at high redshift, challenging conventional scenarios in which supermassive black holes (SMBHs) grow from stellar-mass seeds. We consider a scenario in which the SMBHs are instead supermassive primordial black holes (SMPBHs), formed directly in a decoupled, subdominant dark sector undergoing a first-order phase transition. Unlike conventional stochastic phase transitions, our mechanism is based on the catalysis by domain walls (DWs): most of the Universe completes the transition rapidly, while rare long-lived false-vacuum domains survive because of DW statistics and collapse into PBHs. This mechanism naturally yields SMPBH seeds with masses up to M_\rm PBH∼\mathcalO(10^10) M_⊙, whose abundance can account for the observed LRD population. It also avoids the usual tensions with phase transition completion, ΔN_\rm eff, and large curvature perturbations. The dark phase transition simultaneously generates an ultra-low-frequency stochastic gravitational-wave background peaking near the pulsar-timing-array range, providing a test of this dark-sector origin of LRDs.

@article{2026arXiv260401304G, author = {{Guo}, Jinhui and {Liu}, Jia and {Tanaka}, Masanori and {Wang}, Xiao-Ping and {Xiao}, Huangyu}, title = {{Supermassive Primordial Black Holes from a Catalyzed Dark Phase Transition for Little Red Dots}}, journal = {arXiv e-prints}, keywords = {High Energy Physics - Phenomenology, Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.01304}, pages = {arXiv:2604.01304}, archiveprefix = {arXiv}, eprint = {2604.01304}, primaryclass = {hep-ph}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260401304G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, early universe, exotic physics, jwst, theory}, month_numeric = {4} }

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Back to basics: Little Red Dots as galaxies and dust-obscured AGNs in a synthetic NIRCam sky simulated with L-GalaxiesBH

Diego Herrero-Carrión, Daniele Spinoso, David Izquierdo-Villalba, and 3 more authors

Monthly Notices of the Royal Astronomical Society, Apr 2026

Abs DOI ADS arXiv

The enigmatic Little Red Dots (LRDs) discovered by the James Webb Space Telescope (JWST) exhibit properties challenging their interpretation as common galaxies or active galactic nuclei (AGNs). Understanding their nature is key to placing them within our picture of early galaxy and massive black hole (MBH) evolution. To this aim, we build a realistic comparison between LRD observations with photometric properties of galaxies and AGN simulated by the L-GalaxiesBH model in a NIRCam mock sky. We model stellar continua and emission lines, the MBH emission from accretion disc, infrared radiation from dusty torus, and lines from narrow and broad-line regions, accounting for dust attenuation and obscuration. Using realistic photometric cuts, we select a population of LRDs including both AGN and galaxies. The LRD fraction peaks at 40 per cent () at . Our LRDs are central galaxies spanning . A population of galaxies with appear as LRDs due to older stellar populations. At higher masses, LRDs dominate the halo and stellar mass functions (, ), and the interplay between AGN and galaxy emission drives the LRD selection. AGN dominate rest-frame UV-optical emission, while dust obscuration is secondary. LRDs host lighter MBHs () than non-LRDs (), with fainter emission unable to balance their hosts Balmer breaks. We find no evidence for dominant heavy-seed origin of MBHs. LRD Galaxies (97 per cent hosting MBHs) and LRD AGNs are disc-dominated, with LRD AGNs showing larger bulges formed mainly via disc instabilities.

@article{2026MNRAS.547ag478H, author = {{Herrero-Carri{\'o}n}, Diego and {Spinoso}, Daniele and {Izquierdo-Villalba}, David and {Su}, Tong and {Bonoli}, Silvia and {Renard}, Pablo}, title = {{Back to basics: Little Red Dots as galaxies and dust-obscured AGNs in a synthetic NIRCam sky simulated with L-GalaxiesBH}}, journal = {\mnras}, keywords = {Galaxies: active, Galaxies: high-redshift, Methods: numerical, Quasars: supermassive black holes, Techniques: photometric, Techniques: semi-analytic models, Astrophysics of Galaxies}, year = {2026}, month = apr, volume = {547}, number = {4}, eid = {stag478}, pages = {stag478}, doi = {10.1093/mnras/stag478}, archiveprefix = {arXiv}, eprint = {2511.10725}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.547ag478H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, agn-dominated, dust-reddened, sed, simulation}, month_numeric = {4} }

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Holes in the BH^⋆? AGN signatures in the FUV spectrum of a black-hole dominated Little Red Dot at z=7.04

Xihan Ji, Gabriele Pezzulli, Francesco D’Eugenio, and 15 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

It has been suggested that “Little Red Dots” (LRDs) might be accreting black holes enshrouded by dense gas in a nearly closed geometry, which completely covers the central black hole, leading to an atmosphere-like structure known as the “black-hole star” (\rm BH^⋆). We test this scenario by analysing new JWST spectroscopy in the far ultraviolet (FUV, rest-frame) of the prototypical LRD Abell2744-QSO1, at z=7.04. We found the presence of broad Lyα emission with an FWHM of ∼1000 km/s, and detections of OI, CIV, and/or FeII emission lines. The NIRCam imaging and NIRSpec slit images indicate that the low- velocity component (v≲200 km/s) of Lyα is likely spatially extended, but the high-velocity component (vrsim 200 km/s) of Lyα remains unresolved. Based on the multi-component kinematics and flux of Lyα relative to Balmer lines, we conclude that the observed line profile is unlikely to be broadened by subsequent resonant scattering through the interstellar medium. This suggests that the high-velocity component of Lyα originates in the broad-line region, although resonant scattering in the dense gas likely makes Lyα broader than Hα as observed. The nebular features of this LRD indicate that there is at least one relatively optically thin direction where Lyα can escape from the broad-line region (BLR). We also found indications that photons from the BLR are powering fluorescence of FeII and OI on a larger physical scale. The FUV features thus challenge the fully-covered geometry interpretation and suggest that there are “holes” in the \rm BH^⋆, or the absorbing medium is simply clumpy.

@article{2026arXiv260403370J, author = {{Ji}, Xihan and {Pezzulli}, Gabriele and {D'Eugenio}, Francesco and {Maiolino}, Roberto and {Carniani}, Stefano and {Tacchella}, Sandro and {Jones}, Gareth and {Smith}, Aaron and {Witstok}, Joris and {Fabian}, Andrew C. and {Geris}, Sophia and {Harshan}, Anishya and {Isobe}, Yuki and {Ivey}, Lucy R. and {Juod{\v{z}}balis}, Ignas and {Pascalau}, Robert and {Scholtz}, Jan and {Witten}, Callum}, title = {{Holes in the BH$^\star$? AGN signatures in the FUV spectrum of a black-hole dominated Little Red Dot at $z=7.04$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.03370}, pages = {arXiv:2604.03370}, archiveprefix = {arXiv}, eprint = {2604.03370}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260403370J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, emission lines, jwst, kinematics, spectroscopy}, month_numeric = {4} }

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GLIMPSED: Direct evidence for a fast AGN-driven outflow from a z=6.64 Little Red Dot host galaxy

Damien Korber, Rui Marques-Chaves, Daniel Schaerer, and 15 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

We report the discovery of GLIMPSED-329380, a z=6.64 galaxy behind Abell S1063, which shows signs of an extreme ionised outflow driven by an active galactic nucleus (AGN). The deep JWST/NIRSpec medium grating observations show spatially resolved structures of a host galaxy containing the very fast outflow and an AGN, which we analyse separately. The outflow, mainly traced by broad [O III]\ensuremathλ5008 and H\ensuremathα emissions in the host, reaches a full-width half-maximum velocity of \raisebox-0.5ex\textasciitilde5500km/s, velocities only observed in AGN-dominated systems. From the Balmer decrement, we observe that while the narrow emission lines show no dust attenuation, the outflowing gas is dusty. We use emission lines diagnostics to infer gas abundances within the host galaxy. The oxygen abundance is 12+log(O/H) \raisebox-0.5ex~7.95 (\raisebox-0.5ex\textasciitilde18% solar) and the host is slightly nitrogen-enriched with log(N/O) \raisebox-0.5ex~-0.75. Despite its extreme velocity, the mass loading factor (<0.1) and the kinematic energy of the outflow (\raisebox-0.5ex\textasciitilde10\^43 erg/s) suggest limited impact on star formation. The AGN component shows many similarities with little red dots (LRDs): a characteristic “V-shape”, exponential profile in hydrogen lines, numerous detection of forbidden [Fe II] lines, a Balmer break, and a broad absorption feature at \raisebox-0.5ex\textasciitilde4550 Å. This detection of a fast outflow in an LRD, rare in surveys dominated by low- resolution (e.g. PRISM) spectra, provides direct evidence of AGN activity in these systems.

@article{2026arXiv260408687K, author = {{Korber}, Damien and {Marques-Chaves}, Rui and {Schaerer}, Daniel and {Brammer}, Gabriel and {Aravindan}, Archana and {Basu}, Arghyadeep and {Fei}, Qinyue and {Giovinazzo}, Emma and {Kokorev}, Vasily and {Saldana-Lopez}, Alberto and {Trebitsch}, Maxime and {Atek}, Hakim and {Chisholm}, John and {Endsley}, Ryan and {Fujimoto}, Seiji and {Furtak}, Lukas and {Pan}, Richard and {Naidu}, Rohan P.}, title = {{GLIMPSED: Direct evidence for a fast AGN-driven outflow from a z=6.64 Little Red Dot host galaxy}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.08687}, pages = {arXiv:2604.08687}, archiveprefix = {arXiv}, eprint = {2604.08687}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260408687K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, emission lines, host galaxy, jwst, kinematics}, month_numeric = {4} }

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Little red dots as hidden neutrino sources

Riku Kuze, Kunihito Ioka, Kohta Murase, and 2 more authors

Physical Review D, Apr 2026

Abs DOI ADS arXiv

Little red dots (LRDs) are enigmatic, compact, red galaxies at high redshift, z\ensuremath∼4─7, discovered by the James Webb Space Telescope. Broad emission lines in the absence of x-ray and radio counterparts suggest that they host accreting supermassive black holes embedded in dense gaseous envelopes. This black-hole-envelope configuration facilitates efficient photohadronic interactions and neutrino production. Remarkably, their observed source number density and luminosity are compatible with the energetics of the diffuse neutrino background. We consider that relativistic jets and outflows are launched from the black hole and propagate through low-density polar funnels within envelopes, where particle acceleration and neutrino emission occur. This leads to LRDs being effectively hidden sources. Our analytic and numerical calculations show that, in an optimistic scenario, LRDs can contribute \ensuremath∼30% of the observed diffuse background at TeV─sub-PeV energies, predominantly through photomeson production. At high neutrino energies, \ensuremath≳105.5 GeV, inverse-Compton cooling of muons modifies the resulting flavor ratio, providing a distinctive diagnostic for IceCube-Gen2 and other upcoming neutrino telescopes.

@article{2026PhRvD.113h3048K, author = {{Kuze}, Riku and {Ioka}, Kunihito and {Murase}, Kohta and {Kimura}, Shigeo S. and {Inayoshi}, Kohei}, title = {{Little red dots as hidden neutrino sources}}, journal = {\prd}, keywords = {Astrophysics and astroparticle physics}, year = {2026}, month = apr, volume = {113}, number = {8}, eid = {083048}, pages = {083048}, doi = {10.1103/vbfz-ncxd}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026PhRvD.113h3048K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2601.11203}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, lrdkeys = {abundance, agn-dominated, early universe, theory}, month_numeric = {4} }

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The GlimmIr: Spectroscopic Variability in a z\raisebox-0.5ex\textasciitilde7 LRD Indicates Rapid Changes in Both the Narrow and Broad Line Regions

Erini Lambrides, Taylor A. Hutchison, Rebecca L. Larson, and 39 more authors

arXiv e-prints, Apr 2026

Abs DOI ADS arXiv

The enigmatic population of “Little Red Dots” (LRDs) sit at the center of some of the largest debates in extragalactic astronomy today. The source(s) of ionizing emission and the physical scale over which it governs is still largely unknown. We show for the first time spectroscopic variability in a z \raisebox-0.5ex~7 LRD. Comparing a recently obtained 10.2 hr JWST/NIRSpec F290LP/G395M spectrum via the C3PO survey to an 8.4 hr F290LP/G395M spectrum taken 99 days earlier (\raisebox-0.5ex\textasciitilde13 rest-days) via the THRILS survey, we find a \raisebox-0.5ex\textasciitilde30% $ difference in the continuum and broad-line flux, and a 42% difference between [OIII]5008 flux in the two epochs. Through rigorous testing, we confirm that such differences are not the result of differing MSA slit placements on source nor merely flux calibration offsets. These results are further corroborated by both a similar continuum and [OIII]5008 flux differences found in NIRSpec prism/clear observations of the source at an epoch taken approximately a year earlier than the THRILS observations via RUBIES and an additional observation fortuitously taken during the THRILS epoch (within a rest-day) via the CAPERS survey. Assuming LRDs are a type of accreting black hole system, this implies direct sight-lines must exist from the accretion disk to the surrounding nebular gas on scales beyond the broad-line region, and thus any high-density gas interpretations must allow for covering fractions < 100%. Furthermore, these results show the [OIII] line emission is likely not galaxy process-dominated, with a significant population of the narrow-line emitting gas closest to the broad- line region being directly ionized by the LRD. Finally, these results highlight the need for new approaches in inferring black hole properties of these systems, accounting for the lack of significant ionization via star formation, and/or exploring more exotic host-galaxy conditions at these early epochs.

@article{2026arXiv260425991L, author = {{Lambrides}, Erini and {Hutchison}, Taylor A. and {Larson}, Rebecca L. and {Arrabal Haro}, Pablo and {Papovich}, Casey and {Hu}, Weida and {Cleri}, Nikko J. and {Finkelstein}, Steven L. and {Trump}, Jonathan R. and {Perez-Gonzalez}, Pablo G. and {Wang}, Bingjie and {Kocevski}, Dale D. and {Chisholm}, John and {Secunda}, Amy and {Bosman}, Sarah E. I. and {Akins}, Hollis and {Karmen}, Mitchell and {Dickinson}, Mark and {Bromm}, Volker and {Backhaus}, Bren E. and {Chiaberge}, Marco and {Cooper}, Olivia R. and {Ajay}, Yukta and {Barro}, Guillermo and {Berg}, Danielle A. and {Cann}, Jenna and {Cooper}, M. C. and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Huertas-Company}, Marc and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Lucas}, Ray A. and {Long}, Arianna S. and {Gilli}, Roberto and {Norman}, Colin and {Ptak}, Andrew F. and {Richardson}, Chris T. and {Rigby}, Jane R. and {Vanderhoof}, Brittany N. and {Yung}, L. Y. Aaron and {Zavala}, Jorge A.}, title = {{The GlimmIr: Spectroscopic Variability in a z\raisebox{-0.5ex}\textasciitilde7 LRD Indicates Rapid Changes in Both the Narrow and Broad Line Regions}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.25991}, pages = {arXiv:2604.25991}, doi = {10.48550/arXiv.2604.25991}, archiveprefix = {arXiv}, eprint = {2604.25991}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260425991L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {case study, emission lines, jwst, spectroscopy, variability}, month_numeric = {4} }

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How I Wonder What You Are – JWST’s Little Red Dots do not TWINKLE

Zhaoran Liu, Rohan P. Naidu, Amy Secunda, and 20 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

Little Red Dots (LRDs) are a population of compact, red sources that have emerged as one of the most puzzling findings of JWST. Variability provides a direct probe of their central engines. Here we present the first joint spectroscopic and photometric time-domain study of LRDs undertaken with the JWST TWINKLE slitless spectroscopy program. Surveying the FRESCO GOODS-North legacy field, TWINKLE monitors a complete, Hα-flux-limited sample of 18 LRDs at z = 3.9-6.8, achieving a rest-frame baseline of \sim140-220 days. We detect no variability in photometry, Hα line flux, or line shape across the sample. If LRDs resembled AGN in reverberation mapping samples – the foundation for black hole mass calibrations and luminosity scaling relations – we would expect >10 sources to show measurable fluctuations. Observing none implies a 5.9σ deficit. The non-detections hold across all broad Hα emitters within TWINKLE’s field of view – the 18 V-shaped LRDs as well as 9 non-LRDs. Comparison with simulated light curves disfavors sub-Eddington accretion and is instead consistent with super- Eddington accretion, other mechanisms that suppress variability, or perhaps no AGN whatsoever. If LRDs do harbor black holes, calibrations derived from sub-Eddington systems may not apply, thereby explaining JWST’s apparently “overmassive” black holes. These observations provide unique constraints on the physics of one of the most enigmatic populations discovered by JWST.

@article{2026arXiv260413000L, author = {{Liu}, Zhaoran and {Naidu}, Rohan P. and {Secunda}, Amy and {Greene}, Jenny E. and {Matthee}, Jorryt and {Chisholm}, John and {de Graaff}, Anna and {Robbins}, Luke and {Antwi-Danso}, Jacqueline and {Brammer}, Gabriel and {Sun}, Wendy Q. and {Eilers}, Anna-Christina and {Fujimoto}, Seiji and {Furtak}, Lukas J. and {Kara}, Erin and {Kokorev}, Vasily and {Marchesini}, Danilo and {Oesch}, Pascal A. and {Pierel}, Justin D. R. and {Shen}, Xuejian and {Simcoe}, Robert A. and {Torralba}, Alberto and {Vogelsberger}, Mark}, title = {{How I Wonder What You Are -- JWST's Little Red Dots do not TWINKLE}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.13000}, pages = {arXiv:2604.13000}, archiveprefix = {arXiv}, eprint = {2604.13000}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260413000L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, non-agn, spectroscopy, super-eddington, variability}, month_numeric = {4} }

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Wings of little dots: Exponential broad lines from a stratified BLR

Piero Madau, Roberto Maiolino, Jan Scholtz, and 1 more author

arXiv e-prints, Apr 2026

Abs ADS arXiv

We investigate the origin of the broad exponential wings observed in a significant fraction of the Halpha profiles of JWST-discovered little red dots (LRDs) and little blue dots (LBDs). Recent studies have shown that exponential broad-line profiles are not a prerogative of LRDs, are often also present in LBDs, and need not imply that electron scattering is the dominant broadening mechanism in every source. Motivated by our unification picture in which LRDs are the dust-reddened, high-inclination counterparts of compact blue broad-line AGNs, we model the broad Balmer emission with a virialized, radially stratified broad- line region (BLR). In this framework, the observed profile is the luminosity-weighted superposition of clouds spanning a range of radii and therefore a range of characteristic virial velocities. We show that such a stratified BLR can reproduce the extended exponential-like wings observed in three representative LRDs, without requiring electron scattering to be the primary origin of the broad wings. Our results support a picture in which the broad wings and the line cores encode different physics: the wings arise primarily from virial BLR stratification, whereas the cores retain additional imprints of absorption and radiative transfer in dense gas. The successful fits further suggest that the cloud radial distribution peaks near the dust sublimation radius, while the exponential wings are shaped by the line-emitting inner BLR shells where the higher virial velocities produce the high-velocity tails. This offers a simple physical explanation for the exponential wings of little dots, without invoking exotic new components or scenarios.

@article{2026arXiv260404216M, author = {{Madau}, Piero and {Maiolino}, Roberto and {Scholtz}, Jan and {D'Eugenio}, Francesco}, title = {{Wings of little dots: Exponential broad lines from a stratified BLR}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.04216}, pages = {arXiv:2604.04216}, archiveprefix = {arXiv}, eprint = {2604.04216}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260404216M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, emission lines, jwst, spectroscopy, theory}, month_numeric = {4} }

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Pulsational mass loss from supermassive stars creates the compact shells of Little Red Dots

Devesh Nandal, Igor Chilingarian, Chris Nagele, and 3 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

Little Red Dots (LRDs) have emerged as one of the central puzzles of the JWST era. Their spectra increasingly require dense gas close to the source, yet the physical origin of that cocoon-like structure remains unclear. We examine whether late pulsational mass loss from supermassive stars (SMS)leads to dense gas cocoons. We analyze five accreting GENEC models at different metallicities with characteristic masses of order 10^5 M_⊙, following them through post-accretion evolution with radial pulsation calculations and general relativistic (GR) stability diagnostics. Mass loss during the final stages of evolution occurs not as a steady wind, but through discrete strange-mode ejection episodes. In the Z=10^-2 Z_⊙model, which provides the clearest LRD analogue, four late episodes last 41–282 yr and eject 10–348 M_⊙each, for a total loss of (4.8-10)\times10^2 M_⊙; the final episode alone contributes ≃73% of that budget. Since the last episode dominates the mass-loss, it is the only event sufficiently massive enough to leave behind a compact, optically thick shell extending out to 0.4 pc that reproduces the LRD dense gas cocoon. The final ejecta are H/He dominated but chemically distinctive, with a robust nitrogen-rich composition, \log(\mathrmN/O)\simeq0.13 and \log(\mathrmC/O)≃-0.23. The SMS reaches GR instability at an age of ∼1 Myr and collapses in \sim10^4 s, retaining ∼99% all of its mass. Across the full metallicity range from Pop III to 10^-2 Z_⊙, this shell-ejection channel persists. Pulsational mass-loss from SMSs therefore provides a physically motivated origin for the compact cocoon-like structure implied by LRDs, while remaining the natural progenitors of the massive black hole seeds invoked in direct collapse scenario.

@article{2026arXiv260419988N, author = {{Nandal}, Devesh and {Chilingarian}, Igor and {Nagele}, Chris and {Chisholm}, John and {Bauer}, Franz E. and {Loeb}, Abraham}, title = {{Pulsational mass loss from supermassive stars creates the compact shells of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Astrophysics of Galaxies, Solar and Stellar Astrophysics}, year = {2026}, month = apr, eid = {arXiv:2604.19988}, pages = {arXiv:2604.19988}, archiveprefix = {arXiv}, eprint = {2604.19988}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260419988N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {exotic physics, obscuration, simulation, spectroscopy, theory}, month_numeric = {4} }

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Supermassive stars with embedded stellar black hole cores: dense assembling star clusters as faint multiple Little Red Dot systems

Antti Rantala

arXiv e-prints, Apr 2026

Abs DOI ADS arXiv

Numerical simulations have established that star clusters with densities comparable to the high redshift (z>6-10) James Webb Space Telescope (JWST) proto globular clusters may build up extremely massive (EMSs; m_\mathrm⋆>1000 M_⊙) or even supermassive stars (SMSs; m_\mathrm⋆>10000 M_⊙) and potentially intermediate mass black holes (IMBHs) through runaway stellar collisions. Using direct simulations of assembling star clusters including post-Newtonian black hole dynamics and stellar evolution, we demonstrate that in such dense environments (Σ_\mathrmh rsim 10^6 M_\odotpc^\mathrm-2) stellar BHs (m_∙≲60 M_⊙), driven by rapid mass segregation and relaxation effects within the sphere of influence of the EMSs/SMSs, may strongly interact with the extremely massive stars and become embedded within their gaseous layers. We suggest that this quasi-star (QS) like embedded BH phase is a natural outcome of the runaway formation of EMSs/SMSs in the densest star clusters. The QS phase is orders of magnitude longer in duration than the lifetime of the SMS, enabling an extended growth period by stellar collisions, and allows the formation of embedded gravitational wave sources if the QS captures more than a single stellar BH. The star cluster assembly region sizes (\sim100 pc), QS masses (rsim 10^4 M_⊙) and their proximity to young, massive blue star forming clumps are consistent with the faint population of multiple little red dots (LRDs) recently discovered by the JWST.

@article{2026arXiv260422924R, author = {{Rantala}, Antti}, title = {{Supermassive stars with embedded stellar black hole cores: dense assembling star clusters as faint multiple Little Red Dot systems}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.22924}, pages = {arXiv:2604.22924}, doi = {10.48550/arXiv.2604.22924}, archiveprefix = {arXiv}, eprint = {2604.22924}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260422924R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, exotic physics, jwst, simulation, theory}, month_numeric = {4} }

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The Way We Tally Becomes the Tale: the Impact of Selection Strategies on the Inferred Evolution of Little Red Dots Across Cosmic Time

Pierluigi Rinaldi, Kevin Hainline, Francesco D’Eugenio, and 27 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

Little Red Dots (LRDs) have emerged as a key population linked to early black hole growth, yet photometric selections have predominantly targeted only the most extreme red systems, thereby shaping our current understanding of this new population of objects. In this work, we deliberately explore a broad range of optical redness while enforcing stringent compactness and visual inspection to ensure robustness and minimize contamination. Leveraging the depth and multiwavelength coverage of the JWST Advanced Deep Extragalactic Survey (JADES) data in the GOODS-North and GOODS- South fields, we construct the largest photometric census of LRDs to date in these fields, comprising 412 sources over z\approx2\text–11 across \approx349.6 arcmin^2. We show that classic extreme color cuts isolate only a minor fraction of this population (\lesssim25%), while the majority of LRDs span a broader, largely unexplored parameter space. We quantify how selection strategies impact UV and optical luminosity functions and number density evolution, finding that current demographic trends of LRDs are strongly driven by selection biases and further limited by incomplete identification at both high and low redshift. Spectroscopically confirmed LRDs reveal a continuous range of spectral shapes, consistent with varying Active Galactic Nucleus (AGN) and host contributions in agreement with recent findings. Our results demonstrate that commonly adopted, purity-driven selections bias current demographic constraints toward the most extreme systems, potentially misrepresenting the diversity and evolution of the LRD population. Accounting for these selection effects is essential for interpreting LRDs and their role in early black hole growth.

@article{2026arXiv260407138R, author = {{Rinaldi}, Pierluigi and {Hainline}, Kevin and {D'Eugenio}, Francesco and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Eisenstein}, Daniel J. and {Willmer}, Christopher N. A. and {Carreira}, Courtney and {Robertson}, Brant and {Johnson}, Benjamin D. and {Alberts}, Stacey and {Baker}, William M. and {Bunker}, Andrew J. and {Carniani}, Stefano and {Egami}, Eiichi and {Helton}, Jakob M. and {Ji}, Zhiyuan and {Juod{\v{z}}balis}, Ignas and {Lin}, Xiaojing and {Lyu}, Jianwei and {Ma}, Zheng and {Maiolino}, Roberto and {Parlanti}, Eleonora and {Scholtz}, Jan and {Tacchella}, Sandro and {Venturi}, Giacomo and {Williams}, Christina C. and {Willott}, Chris and {Witstok}, Joris and {Sun}, Yang and {Wu}, Zihao}, title = {{The Way We Tally Becomes the Tale: the Impact of Selection Strategies on the Inferred Evolution of Little Red Dots Across Cosmic Time}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2026}, month = apr, eid = {arXiv:2604.07138}, pages = {arXiv:2604.07138}, archiveprefix = {arXiv}, eprint = {2604.07138}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260407138R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, jwst, multi-wavelength, photometry, sample selection}, month_numeric = {4} }

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Paschen Jumps in Little Red Dots: Evidence for Nebular Continua

Albert Sneppen, James H. Matthews, Darach Watson, and 6 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

“Little Red Dots” (LRDs) are broad-line sources at high redshift, initially identified by their compact morphologies, red colours and prominent Balmer breaks. The origin of their optical-to- near-infrared continua is debated, with proposed explanations ranging from direct recombination emission to thermalised blackbodies from stellar-like atmospheres. Here we report evidence for Paschen jumps in a subset of LRDs, consistent with free-bound recombination to hydrogen n=3. The Paschen and Brackett continuum shapes across the sample are consistent with minimally reddened emission from low-temperature gas with T_e\lesssim10 000 K, while the presence of Paschen jump signatures limits scenarios in which the emission is thermalised. Further, the extreme Hα equivalent widths and the tight observed correlation between Hα and the continuum follow naturally if both originate in recombination emission. This provides an observational upper limit on the contribution of any direct AGN accretion component and any stellar-atmosphere-like component, as well as on the fraction of line emission that can be thermalised as it traverses the cocoon. Ultimately, nebular radiative-transfer models provide a self-consistent explanation of the continuum, line strengths and line profiles without requiring multiple separately fitted components.

@article{2026arXiv260409399S, author = {{Sneppen}, Albert and {Matthews}, James H. and {Watson}, Darach and {Cameron}, Alex J. and {Sim}, Stuart A. and {Witstok}, Joris and {Brammer}, Gabriel B. and {Heintz}, Kasper E. and {Nikopoulos}, Georgios}, title = {{Paschen Jumps in Little Red Dots: Evidence for Nebular Continua}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.09399}, pages = {arXiv:2604.09399}, archiveprefix = {arXiv}, eprint = {2604.09399}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260409399S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, non-agn, sed, spectroscopy}, month_numeric = {4} }

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SPURS: Evidence for Clumpy Neutral Envelopes and Ionized IGM Surrounding Little Red Dots in Abell 2744 from Ultra-Deep Rest-UV Spectroscopy

Mengtao Tang, Daniel P. Stark, Charlotte A. Mason, and 14 more authors

arXiv e-prints, Apr 2026

Abs ADS arXiv

Rest-frame ultraviolet (UV) spectra of Little Red Dots (LRDs) often show Lyα emission. Along with broad Balmer emission, LRDs are expected to produce broad Lyα emission. However, the large column density of neutral gas invoked to explain the Balmer break should significantly redshift and further broaden the Lyα line, making it challenging to detect without sensitive, moderate-resolution spectra. We present ultra-deep (29 hours) G140M JWST/NIRSpec observations covering the rest-UV of two LRDs in Abell2744 from the SPURS Cycle 4 Large Program. One of our targets is Abell2744-QSO1, a gravitationally-lensed LRD at z=7.04 with faint UV emission (M_\rm UV=-16.9), and the other source (UNCOVER-2476) is newly-confirmed at z=4.02 with a very bright UV continuum (M_\rm UV=-19.6). We find that Abell2744-QSO1 has a broad Lyα profile, along with narrow CIV, FeII\lambda1786, and OI\lambda1302 emission. The Lyα profile suggests an origin similar to the broad Hα, but the line is considerably less redshifted than expected from existing dense gas models. We show that the line profile can be explained if the dense neutral gas is clumpy, allowing Lyα to escape by scattering off of the clump surfaces. We find that UNCOVER-2476 has narrow [NeIV] emission, indicating either a hard radiation field or shocks. We confirm two close neighbors with Lyα emission around Abell2744-QSO1, indicating it traces a dense environment that may have ionized its surrounding IGM. We suggest that LRDs may preferentially trace bubbles carved by their dense environments, contributing to the prevalence of Lyα in the population.

@article{2026arXiv260403563T, author = {{Tang}, Mengtao and {Stark}, Daniel P. and {Mason}, Charlotte A. and {Chen}, Zuyi and {Katz}, Harley and {Gronke}, Max and {Furtak}, Lukas J. and {Chang}, Seok-Jun and {Matthee}, Jorryt and {Whitler}, Lily and {Zitrin}, Adi and {Endsley}, Ryan and {Gelli}, Viola and {Roychowdhury}, Tamojeet and {Senchyna}, Peter and {Topping}, Michael W. and {Zhang}, Meng}, title = {{SPURS: Evidence for Clumpy Neutral Envelopes and Ionized IGM Surrounding Little Red Dots in Abell 2744 from Ultra-Deep Rest-UV Spectroscopy}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = apr, eid = {arXiv:2604.03563}, pages = {arXiv:2604.03563}, archiveprefix = {arXiv}, eprint = {2604.03563}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260403563T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, obscuration, spectroscopy}, month_numeric = {4} }

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The X-ray weakness of little red dots and JWST-selected AGN: Comparison with local AGN in different accretion regimes

A. Tortosa, C. Ricci, P. Du, and 5 more authors

Astronomy & Astrophysics, Apr 2026

Abs DOI ADS arXiv

We investigate the origin of the observed X-ray weakness in high z little red dots (LRDs) and other JWST-selected broad line active galactic nuclei (AGN) by comparing their X-ray and optical properties with those of a diverse sample of low z AGN, including super-Eddington accreting massive black holes (SEAMBHs), narrow-line Seyfert 1 galaxies (NLS1s), and type I AGN from large surveys (e.g. BASS, SDSS). Using a heterogeneous set of AGN samples spanning a wide range of redshift and accretion rates, we examine the relations between X-ray luminosity (L_2 \ensuremath- 10 keV), broad H\ensuremathα line luminosity (L_H\ensuremathα), Eddington ratio (\ensuremathλ_Edd), bolometric luminosity (L_bol), and X-ray-to-bolometric luminosity correction (\ensuremathκ_bol, X), and we explore whether high z sources may represent analogues of local highly accreting systems. While a few LRDs and JWST-selected AGN are consistent with the SEAMBH population in the L_2 \ensuremath- 10 keV/L_H\ensuremathα versus \ensuremathλ_Edd plane, most lie below it, suggesting either more extreme accretion conditions, suppressed coronal emission or heavy obscuration. We identify an anti- correlation between L_2 \ensuremath- 10 keV/L_H\ensuremathα and \ensuremathλ_Edd in the low z, high-\ensuremathλ_Edd subsample of sources, consistent with theoretical expectations of slim-disc accretion. We further show that, for SEAMBHs, H\ensuremathα-based bolometric luminosities underestimate spectral energy distribution-based values even after dust correction, reinforcing the need for SED-based estimates. We find that SEAMBHs, LRDs, and JWST-selected AGN occupy a similar high-\ensuremathκ_bol, X regime, indicating that the relative deficit of X-ray emission compared to the bolometric output could potentially support the view that suppression of the hot corona emission is a common feature of highly accreting systems across cosmic time. However, the X-ray measurements of high z sources are largely based on observed upper limits and generally do not account for heavy or Compton- thick obscuration, in which case the intrinsic L_2 \ensuremath- 10 keV could be substantially higher than observed. Our results are consistent with the idea that the observed X-ray weakness of LRDs and JWST-selected AGN may be linked to the physics of highly accreting SMBHs, but alternative explanations, including heavy obscuration, systematics in BH mass estimates, or a combination of intrinsic coronal suppression and absorption, remain viable. Moreover, observational limitations at high z, including instrumental sensitivity and the steep X-ray spectra expected for highly accreting systems, likely further suppress the detected X-ray signal. Disentangling the roles of accretion physics and obscuration will require deeper, higher-resolution X-ray observations with next-generation facilities, which will be crucial for establishing whether these sources represent genuine high z counterparts of local highly accreting AGN.

@article{2026A&A...708A.293T, author = {{Tortosa}, A. and {Ricci}, C. and {Du}, P. and {Venturi}, G. and {Ho}, L. C. and {Li}, R. and {Wang}, J.-M. and {Berton}, M.}, title = {{The X-ray weakness of little red dots and JWST-selected AGN: Comparison with local AGN in different accretion regimes}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift, galaxies: nuclei, quasars: general, quasars: supermassive black holes, X-rays: galaxies}, year = {2026}, month = apr, volume = {708}, eid = {A293}, pages = {A293}, doi = {10.1051/0004-6361/202557444}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...708A.293T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, eprint = {2603.10162}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, lrdkeys = {jwst, local counterpart, obscuration, super-eddington, x-ray}, month_numeric = {4} }

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Growth of high-redshift quasars from fermion dark matter seeds

Yu Wang and Remo Ruffini

Journal of High Energy Astrophysics, Apr 2026

Abs DOI ADS arXiv

Quasars hosting \ensuremath≳ 10^9 M_\ensuremath⊙ black holes at z > 6 challenge growth scenarios that start from light seeds and assume accretion within already formed galaxies. Motivated by the James Webb Space Telescope (JWST) discovery of Little Red Dots (LRDs), which suggests that \ensuremath∼ 10^6 M_\ensuremath⊙ black holes can be active in compact, pre-galactic environments, we revisit early black hole growth with a minimal cosmology-based framework. We model the accretion history as the smaller of the Bondi inflow rate and the Eddington-limited rate, where the Bondi rate is set by the supply of overdense primordial gas whose density declines with cosmic expansion, and the Eddington rate captures regulation by radiative feedback. By fitting the observed masses and luminosities of J0313─1806 (z=7.64) and J0100+2802 (z=6.30) with Bayesian inference, we infer initial conditions that favor massive seed black holes with initial mass M_0 \ensuremath∼ 10^6 M_\ensuremath⊙, formed at z\ensure math∼20\ensuremath-30 in environments with baryonic overdensity factors f_\ensuremathρ \ensuremath≳ 50 relative to the cosmic mean. The resulting growth histories include a prolonged supply-limited stage, and they reproduce the observed quasar masses without requiring sustained Eddington accretion or any super-Eddington episodes. The inferred seed mass scale is consistent with black holes produced by the collapse of quantum- degenerate fermion dark matter cores, providing a physically defined pathway to massive seeds at the redshifts implied by LRD phenomenology.

@article{2026JHEAp..5200576W, author = {{Wang}, Yu and {Ruffini}, Remo}, title = {{Growth of high-redshift quasars from fermion dark matter seeds}}, journal = {Journal of High Energy Astrophysics}, keywords = {Accretion, Active galactic nuclei, Astrophysical black holes, High-redshift quasars, Little red dots, Fermion dark matter, Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = apr, volume = {52}, eid = {100576}, pages = {100576}, doi = {10.1016/j.jheap.2026.100576}, archiveprefix = {arXiv}, eprint = {2602.05135}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026JHEAp..5200576W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, exotic physics, heavy seed, theory}, month_numeric = {4} }

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Radiation GRMHD Models of Accretion onto Stellar-mass Black Holes. II. Super-Eddington Accretion

Lizhong Zhang, James M. Stone, Christopher J. White, and 3 more authors

The Astrophysical Journal, Apr 2026

Abs DOI ADS arXiv

We present a comprehensive analysis of super-Eddington black hole accretion simulations that solve the GRMHD equations coupled with angle-discretized radiation transport. The simulations span a range of accretion rates, two black hole spins, and two magnetic field topologies, and include resolution studies as well as comparisons with nonradiative models. Super-Eddington accretion flows consistently develop geometrically thick disks supported by radiation pressure, regardless of magnetic field configuration. Radiation generated in the inner disk drives substantial outflows, forming conical funnel regions that limit photon escape and result in very low radiation efficiency. The accretion flows are highly turbulent, with thermal energy transport dominated by radiation advection rather than diffusion. Angular momentum is primarily carried outward by Maxwell stress, with turbulent Reynolds stress playing a subdominant role. Both strong and weak jets are produced. Strong jets arise from sufficient net vertical magnetic flux and rapid black hole spin, and they can effectively evacuate the funnel, enabling radiation to escape through strong geometric beaming. In contrast, weak jets fail to clear the funnel, which becomes obscured by radiation-driven outflows and leads to distinct observational signatures. Spiral structures are observed in the plunging region, behaving like density waves. These super- Eddington models are applicable to a variety of astronomical systems, including ultraluminous X-ray sources, little red dots, and black hole transients.

@article{2026ApJ..1001..138Z, author = {{Zhang}, Lizhong and {Stone}, James M. and {White}, Christopher J. and {Davis}, Shane W. and {Jiang}, Yan-Fei and {Mullen}, Patrick D.}, title = {{Radiation GRMHD Models of Accretion onto Stellar-mass Black Holes. II. Super-Eddington Accretion}}, journal = {\apj}, keywords = {Radiative magnetohydrodynamics, General relativity, Black hole physics, Accretion, Jets, Ultraluminous x-ray sources, 2009, 641, 159, 14, 870, 2164, High Energy Astrophysical Phenomena}, year = {2026}, month = apr, volume = {1001}, number = {2}, eid = {138}, pages = {138}, doi = {10.3847/1538-4357/ae5521}, archiveprefix = {arXiv}, eprint = {2509.10638}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1001..138Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {kinematics, simulation, super-eddington, theory, x-ray}, month_numeric = {4} }

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Red and tiny: dusty dwarfs and little red dots as seen by ELT

Laura Bisigello

Video Memorie della Societa Astronomica Italiana, Mar 2026

DOI ADS

@article{2026VMSAI...2....7B, author = {{Bisigello}, Laura}, title = {{Red and tiny: dusty dwarfs and little red dots as seen by ELT}}, journal = {Video Memorie della Societa Astronomica Italiana}, year = {2026}, month = mar, volume = {2}, eid = {7}, pages = {7}, doi = {10.36116/VIDEOMEM\_2.2026.07}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026VMSAI...2....7B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, morphology, non-agn, simulation, spectroscopy}, month_numeric = {3} }

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Little Red Dots

Rebecca Boyle

Scientific American, Mar 2026

DOI ADS

@article{2026SciAm.334...36B, author = {{Boyle}, Rebecca}, title = {{Little Red Dots}}, journal = {Scientific American}, year = {2026}, month = mar, volume = {334}, number = {3}, pages = {36}, doi = {10.1038/scientificamerican032026-7sL4BhJRPpda6Lz78S6joL}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026SciAm.334...36B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, catalog, early universe, multi-wavelength, review}, month_numeric = {3} }

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Pulsational Instability of Quasi-stars: Interpreting the Variability of Little Red Dots

Matteo Cantiello, Jake B. Hassan, Rosalba Perna, and 5 more authors

The Astrophysical Journal Letters, Mar 2026

Abs DOI ADS arXiv

The JWST discovery of “little red dots” (LRDs) has revealed a population of compact, red sources at z \ensuremath∼ 5─10 that likely host supermassive black holes. Recent observations of the gravitationally lensed LRD R2211-RX1 reveal century-scale photometric variability and a hysteresis loop in the luminosity─temperature plane, strongly suggesting that the optical emission originates from a pulsating, stellar-like photosphere rather than an accretion disk. This supports the “quasi-star” hypothesis, where a rapidly growing black hole seed is embedded within a massive, radiation-pressure supported envelope. Here, we investigate the pulsational stability of these envelopes using the stellar evolution code MESA coupled with the nonadiabatic oscillation code GYRE. We identify a theoretical “quasi-star instability strip” with a blue edge at T_eff ≍ 5000 \ensuremath- 5200 K. Models hotter than this threshold are stable, consistent with the nonvariable LRD R2211-RX2 (T_eff ≍ 5000 K), while cooler models are unstable to radial pulsations driven by the \ensuremathκ-mechanism in helium and hydrogen ionization zones. For quasi-star masses in the range M_\ensuremath⋆ \ensuremath∼ 10^4─10^5 M_\ensuremath⊙, we find that the unstable fundamental radial modes (\ensuremath\ell = 0, n_p = 1) have periods in the range \ensuremath∼20─180 yr. The first overtone (\ensuremath\ell = 0, n_p = 2) is also unstable or marginally stable in some of our models, with typical pulsation timescales \ensuremath∼10─30 yr. These oscillations match the comoving frame variability timescale of RX1. We argue that these violent pulsations likely drive enhanced mass loss analogous to super-AGB winds, which could affect the duration of the quasi-star phase and regulate the final mass of the seeded black hole.

@article{2026ApJ..1000L...4C, author = {{Cantiello}, Matteo and {Hassan}, Jake B. and {Perna}, Rosalba and {Armitage}, Philip J. and {Begelman}, Mitchell C. and {Jiang}, Yan-Fei and {Ryu}, Taeho and {Townsend}, Richard H. D.}, title = {{Pulsational Instability of Quasi-stars: Interpreting the Variability of Little Red Dots}}, journal = {\apjl}, keywords = {Supermassive black holes, Stellar physics, Stellar pulsations, Stellar evolution, High-redshift galaxies, 1663, 1621, 1625, 1599, 734}, year = {2026}, month = mar, volume = {1000}, number = {1}, eid = {L4}, pages = {L4}, doi = {10.3847/2041-8213/ae4729}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1000L...4C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, exotic physics, jwst, theory, variability}, eprint = {2512.17997}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, month_numeric = {3} }

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A z ≃ 0.4 Galaxy Reflecting the High-redshift Little Red Dots: An Extended Starburst with an Overmassive Black Hole

Xiaoyang Chen, Kohei Ichikawa, Masayuki Akiyama, and 10 more authors

The Astrophysical Journal, Mar 2026

Abs DOI ADS arXiv

One of the most remarkable discoveries of JWST is a population of compact, red sources at z > 4, commonly referred to as Little Red Dots (LRDs). Spectroscopic identifications reported that most LRDs are active galactic nuclei, which are preferentially found around z \ensuremath∼ 6 and could imply a key phase in the formation and growth of black holes (BHs) in the early Universe. Photometric surveys at lower redshift have recently been carried out to trace their evolution across cosmic time, and a small number of LRD-like galaxies have been spectroscopically identified at both Cosmic Noon and in the local Universe. Here we report the discovery of one of the lowest-z LRD-like galaxies, J204837.26-002437.2 (hereafter J2048) at z = 0.4330, using new Gemini-N/GMOS integral field unit observations combined with archival multiband photometric spectral energy distribution data. The GMOS data reveal extended blue emission from starburst with a star formation rate of 400 M_\ensuremath⊙ yr^\ensuremath-1, together with an extended, highly fast ionized outflow. This is the first spectroscopic confirmation of extended host emission and outflow in an LRD-like galaxy, providing a unique laboratory for understanding the nature of their high-redshift counterparts. Moreover, J2048 would host an extremely overmassive BH with a BH-to-stellar mass ratio of ≃60%, with the BH mass and host stellar mass estimated to be 10^10.2 and 10^10.4M_\ensuremath⊙, respectively. We discuss the origin and evolutionary fate of J2048, and the implications that such low-z analogs have for interpreting the properties of high-z LRDs.

@article{2026ApJ...999...30C, author = {{Chen}, Xiaoyang and {Ichikawa}, Kohei and {Akiyama}, Masayuki and {Inayoshi}, Kohei and {Inoue}, Akio K. and {Onoue}, Masafusa and {Toba}, Yoshiki and {Zavala}, Jorge and {Bakx}, Tom and {Kawaguchi}, Toshihiro and {Lee}, Kianhong and {Matsumoto}, Naoki and {Vijarnwannaluk}, Bovornpratch}, title = {{A z ≃ 0.4 Galaxy Reflecting the High-redshift Little Red Dots: An Extended Starburst with an Overmassive Black Hole}}, journal = {\apj}, keywords = {Active galactic nuclei, Ultraluminous infrared galaxies, Supermassive black holes, AGN host galaxies, Galaxy evolution, 16, 1735, 1663, 2017, 594}, year = {2026}, month = mar, volume = {999}, number = {1}, eid = {30}, pages = {30}, doi = {10.3847/1538-4357/ae3683}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...999...30C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, heavy seed, kinematics, spectroscopy, starburst}, eprint = {2510.02801}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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A PANORAMIC of UV-optical morphologies of “Little Red Dots”: Two groups of LRDs distinguished by UV half-light radius

Aidan P. Cloonan, Katherine E. Whitaker, Sinclaire M. Manning, and 13 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

Among the most remarkable results from JWST is the discovery of abundant, compact, and very red sources in the early Universe known as “Little Red Dots” (LRDs). The relative degree to which starlight and active galactic nuclei (AGN) drive the rest- frame UV and optical emission from LRDs remains unclear. With a large sample of LRDs selected photometrically from the pure- parallel PANORAMIC survey, we study their morphology as a function of rest-wavelength and find that the rest-UV light is typically more extended than the rest-optical. This result holds both when measuring LRD sizes with a single Sérsic profile and when comparing the fraction of light from a point source via joint PSF+Sérsic modeling. A shift occurs at the Balmer break, with LRDs becoming highly compact and unresolved (R_50,\rmopt\lesssim100;\rmpc) in the rest-optical relative to the rest-UV. When splitting the sample at the Balmer break into those that are resolved and unresolved, a stacking analysis demonstrates that the latter are compact (R_50\lesssim100;\rmpc) on average across the full rest- UV-optical spectrum. Conversely, those LRDs resolved at the break show extended UV emission (R_50,\rmUV>200;\rmpc) on average. We find a similar dichotomy when repeating with a spectroscopic sample. Altogether, these results are consistent with the rest-UV emission driven by a combination of emission from starlight and a dense, dust-poor cloud of hydrogen gas enveloping an AGN. Differences between LRDs in the relative contribution from the AGN and starlight could reflect an ensemble of black hole seed masses, where a heavier seed produces an LRD of smaller R_50,\rmUV.

@article{2026arXiv260324700C, author = {{Cloonan}, Aidan P. and {Whitaker}, Katherine E. and {Manning}, Sinclaire M. and {Williams}, Christina C. and {Greene}, Jenny E. and {Oesch}, Pascal A. and {Weibel}, Andrea and {Brammer}, Gabriel and {de Graaff}, Anna and {Hviding}, Raphael E. and {Dayal}, Pratika and {Jespersen}, Christian Kragh and {Ji}, Zhiyuan and {Labbe}, Ivo and {Xiao}, Mengyuan and {Zhang}, Yunchong}, title = {{A PANORAMIC of UV-optical morphologies of ``Little Red Dots'': Two groups of LRDs distinguished by UV half-light radius}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = mar, eid = {arXiv:2603.24700}, pages = {arXiv:2603.24700}, archiveprefix = {arXiv}, eprint = {2603.24700}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260324700C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, composite, early universe, morphology, starburst}, month_numeric = {3} }

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The X-Ray Dot: Exotic Dust or a Late-stage Little Red Dot?

Raphael E. Hviding, Anna de Graaff, Hanpu Liu, and 15 more authors

The Astrophysical Journal Letters, Mar 2026

Abs DOI ADS arXiv

JWST’s “little red dots” (LRDs) are increasingly interpreted as active galactic nuclei (AGN) obscured by dense thermalized gas rather than dust as evidenced by their X-ray weakness, blackbody-like continua, and Balmer line profiles. Key questions are how LRDs connect to standard UV-luminous AGN, whether transitional phases exist, and whether they are observable. We present the “X-ray dot” (XRD), a compact source at z = 3.28 observed by the NIRSpec Wide Guaranteed Time Observation survey. The XRD exhibits LRD hallmarks: a blackbody-like (T_eff ≃ 6400 K) red continuum, a faint but blue rest-UV excess, falling mid-IR emission, and broad Balmer lines (FWHM \ensuremath∼ 2700─3200 km s^\ensuremath-1). Unlike LRDs, however, it is remarkably X-ray luminous (L_2\ensuremath-10 keV = 10^44.18 erg s^\ensuremath-1) and has a continuum inflection that is blueward of the Balmer limit. We find that the red rest-optical and blue mid-IR continuum cannot be reproduced by standard dust-attenuated AGN models without invoking extremely steep extinction curves, nor can the weak mid-IR emission be reconciled with well-established X-ray─torus scaling relations. We therefore consider an alternative scenario: the XRD may be an LRD in transition, where the gas envelope dominates the optical continuum but optically thin sight lines allow X-rays to escape. The XRD may thus provide a physical link between LRDs and standard AGN, offering direct evidence that LRDs are powered by supermassive black holes and providing insight into their accretion properties.

@article{2026ApJ..1000L..18H, author = {{Hviding}, Raphael E. and {de Graaff}, Anna and {Liu}, Hanpu and {Goulding}, Andy D. and {Ma}, Yilun and {Greene}, Jenny E. and {Boogaard}, Leindert A. and {Bunker}, Andrew J. and {Cleri}, Nikko J. and {Franx}, Marijn and {Hirschmann}, Michaela and {Leja}, Joel and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Setton}, David J. and {{\"U}bler}, Hannah and {Venturi}, Giacomo and {Wang}, Bingjie}, title = {{The X-Ray Dot: Exotic Dust or a Late-stage Little Red Dot?}}, journal = {\apjl}, keywords = {Active galactic nuclei, X-ray quasars, High-redshift galaxies, 16, 1821, 734}, year = {2026}, month = mar, volume = {1000}, number = {1}, eid = {L18}, pages = {L18}, doi = {10.3847/2041-8213/ae4c88}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1000L..18H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, jwst, sed, spectroscopy, x-ray}, eprint = {2601.09778}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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JWST Reveals Two Overmassive Black Hole Candidates in Dwarf Galaxies at z ≈0.7: Pushing Black Hole Searches into the Dwarf-Galaxy Regime

E. Iani, P. Rinaldi, A. Torralba, and 35 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

We report the discovery and characterization of two compact galaxies, Pelias and Neleus, at z \raisebox-0.5ex~0.71 and z \raisebox-0.5ex~0.75, identified in MACS J0416.1-2403 and GOODS-North. Both exhibit unusual spectral energy distributions (SEDs), with very blue rest-frame UV- optical emission and a steep rise toward near- and mid-infrared wavelengths. JWST/NIRISS and JWST/NIRSpec spectroscopy show strong rest-frame optical lines ([O III] 4959,5007 and Halpha) with extreme equivalent widths (>= 1000 Angstrom), indicating young burst-dominated populations with low metallicities (Z \raisebox-0.5ex~0.1-0.4 Zsun), low dust attenuation (Av \raisebox-0.5ex~0.2 mag), and stellar masses of Mstar \raisebox-0.5ex~10\^7 Msun. Nonetheless, JWST/MIRI photometry reveals a strong mid- infrared excess that cannot be explained by stellar populations or star-formation-heated dust alone, requiring a hot-dust component most naturally associated with a deeply embedded active galactic nucleus (AGN). SED modelling yields log10(Lbol [erg/s]) \raisebox-0.5ex~43.7-44.0, implying black hole masses of log10(MBH [Msun]) \raisebox-0.5ex~5.7-6.7 under the assumption of Eddington-limited accretion. Given the very low stellar masses of the hosts, this corresponds to black-hole-to-stellar mass ratios of about 6-60%, well above the extrapolation of local scaling relations. The lack of X-ray detections suggests that the accretion may be either heavily obscured or intrinsically X-ray weak. Their SEDs also resemble those of Blue Excess Hot Dust Obscured Galaxies and show the characteristic V-shaped continuum seen in Little Red Dots, although with the inflection occurring at redder wavelengths.

@article{2026arXiv260317967I, author = {{Iani}, E. and {Rinaldi}, P. and {Torralba}, A. and {Lyu}, J. and {Navarro-Carrera}, R. and {Rieke}, G. H. and {Sun}, F. and {Willott}, C. and {Zhu}, Y. and {Alonso-Herrero}, A. and {Annunziatella}, M. and {Bergamini}, P. and {Caputi}, K. and {Catone}, M. and {Colina}, L. and {Cooper}, R. and {Costantin}, L. and {Crespo G{\'o}mez}, A. and {Desprez}, G. and {Di Cesare}, C. and {Hayes}, M. J. and {Jermann}, I. and {Kotiwale}, G. and {Kramarenko}, I. and {Langeroodi}, D. and {Mascia}, S. and {Matthee}, J. and {Melinder}, J. and {Muzzin}, A. and {Navarrete}, B. and {Noirot}, G. and {{\"O}stlin}, G. and {Pacucci}, F. and {Rodighiero}, G. and {Sawicki}, M. and {Sun}, Y. and {Wu}, Z. and {Yang}, G.}, title = {{JWST Reveals Two Overmassive Black Hole Candidates in Dwarf Galaxies at z $\approx$ 0.7: Pushing Black Hole Searches into the Dwarf-Galaxy Regime}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = mar, eid = {arXiv:2603.17967}, pages = {arXiv:2603.17967}, archiveprefix = {arXiv}, eprint = {2603.17967}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260317967I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, emission lines, jwst, sed}, month_numeric = {3} }

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Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts

Kohei Inayoshi, Kohta Murase, and Kazumi Kashiyama

The Astrophysical Journal, Mar 2026

Abs DOI ADS arXiv

The birth of seeds of massive black holes (BHs) and nascent galaxies at cosmic dawn takes place in dense gaseous environments, which play a crucial role in shaping their coevolution and radiation spectra. We investigate gas accretion during the assembly of massive halos with M_h \ensuremath≳ 10^10\ensuremath-10^11 M_\ensuremath⊙ at redshifts z ≃ 4─10, driving both rapid BH feeding and concurrent nuclear starbursts. As the BH grows to \ensuremath∼10^6\ensuremath-10^7 M_\ensuremath⊙ via super-Eddington accretion, the accretion power inflates a dense envelope whose effective temperature approaches the Hayashi limit at T_eff ≃ 5000 K, producing red optical emission, while a coeval young stellar population of \ensuremath∼10^7 M_\ensuremath⊙ provides blue UV emission. This early coevolving system naturally reproduces the characteristic spectral features of the so-called little red dots (LRDs), a population of broad-line active galactic nuclei (AGNs), including the V-shaped UV-to-optical spectra and weakness of X-ray, infrared, and radio emission. Massive stars in the nuclear starburst soon explode as supernovae, injecting energy and momentum that expel gas from the nucleus, quench gas supply to the BH envelope, and ultimately drive a transition into normal AGN phases. For individual LRDs, the optical-to-UV luminosity ratio remains nearly constant at L_opt/L_UV ≃ 2─10 from the onset of accretion bursts for ≃15 Myr, one-third of the Salpeter time, until quenching by stellar feedback. While this ratio is sustained for the LRD population at z ≃ 4─8, it declines toward lower redshifts, as BHs can no longer maintain red envelopes, thereby losing the LRD characteristics.

@article{2026ApJ..1000...90I, author = {{Inayoshi}, Kohei and {Murase}, Kohta and {Kashiyama}, Kazumi}, title = {{Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts}}, journal = {\apj}, keywords = {Supermassive black holes, High-redshift galaxies, Quasars, 1663, 734, 1319}, year = {2026}, month = mar, volume = {1000}, number = {1}, eid = {90}, pages = {90}, doi = {10.3847/1538-4357/ae42ce}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1000...90I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, simulation, starburst, super-eddington, theory}, eprint = {2509.19422}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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BlackTHUNDER: Shedding light on a dormant and extreme little red dot at z = 8.50

Gareth C. Jones, Hannah Übler, Roberto Maiolino, and 17 more authors

Monthly Notices of the Royal Astronomical Society, Mar 2026

Abs DOI ADS arXiv

Recent photometric surveys with James Webb Space Telescope (JWST) have revealed a significant population of mysterious objects with red colours, compact morphologies, frequent signs of active galactic nucleus (AGN) activity, and negligible X-ray emission. These ’little red dots’ (LRDs) have been explored through spectral and photometric studies, but their nature is still under debate. As part of the BlackTHUNDER survey, we have observed UNCOVER_20466, one of the most distant LRDs known (), with the JWST/NIRSpec Integral Field Unit (IFU). Previous JWST/NIRCam and JWST/NIRSpec MSA observations of this source revealed its LRD nature, as well as the presence of an AGN. Using our NIRSpec IFU data, we confirm that UNCOVER_20466 is an LRD (based on spectral slopes and compactness) that contains an overmassive black hole. However, our observed Balmer decrements do not suggest strong dust attenuation, resulting in a lower -based bolometric luminosity and () than previously found. This source lies on local relations between and , suggesting that this could be a progenitor of the core of a lower-redshift galaxy. We explore the possible evolution of this source, finding evidence for substantial black hole accretion in the past and a likely origin as a heavy seed at high redshift (). emission is strongly detected, implying . The extremely high / ratio is indicative of not only AGN photoionization and heating, but also extremely high densities (), suggesting that this black hole at such high redshift may be forming in an ultra-dense protogalaxy.

@article{2026MNRAS.546ag115J, author = {{Jones}, Gareth C. and {{\"U}bler}, Hannah and {Maiolino}, Roberto and {Ji}, Xihan and {Marconi}, Alessandro and {D'Eugenio}, Francesco and {Arribas}, Santiago and {Bunker}, Andrew J. and {Carniani}, Stefano and {Charlot}, St{\'e}phane and {Cresci}, Giovanni and {Inayoshi}, Kohei and {Isobe}, Yuki and {Juod{\v{z}}balis}, Ignas and {Mazzolari}, Giovanni and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Perna}, Michele and {Schneider}, Raffaella and {Scholtz}, Jan and {Tacchella}, Sandro}, title = {{BlackTHUNDER: Shedding light on a dormant and extreme little red dot at z = 8.50}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: high-redshift, quasars: supermassive black holes}, year = {2026}, month = mar, volume = {546}, number = {3}, eid = {stag115}, pages = {stag115}, doi = {10.1093/mnras/stag115}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.546ag115J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, early universe, heavy seed, jwst, spectroscopy}, eprint = {2509.20455}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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A possible pathway to UHZ1-type systems at z \ensuremath∼ 10 by heterogeneous mass primordial black holes as dark matter

Alexander Kashlinsky, Fernando Atrio-Barandela, and Diego Martı́n-González

Monthly Notices of the Royal Astronomical Society, Mar 2026

Abs DOI ADS arXiv

Recent space-based observations discovered several unusual objects, exhibiting similar properties, at redshifts . Among them is the UHZ1 system at , containing in stars, with a similarly massive central black hole of . Here we propose a possible mechanism for forming such systems which hinges on the presence of primordial black holes (PBHs) covering a range of masses while contributing a significant fraction of the dark matter (DM). We evaluate the accurate expression for the small-scale power responsible for the collapse of the first haloes in the presence of the PBH population. The extra power in the matter density field, produced by the granulation term, will cause an earlier collapse of DM haloes, populated by PBHs of different masses. In these collapsed and virialized systems the PBHs will undergo 2-body relaxation, driving the more massive PBHs to the halo centre under dynamical friction. We quantify this evolution for a distribution of PBH orbital parameters and halo properties. The analysis shows that PBHs can have appropriate mass functions capable of producing systems with parameters similar to what is observed for UHZ1. We suggest that the proposed mechanism could account for a subset of other systems newly discovered with the James Webbn Space Telescope (JWST) at high redshifts, including the Little Red Dots.

@article{2026MNRAS.546ag124K, author = {{Kashlinsky}, Alexander and {Atrio-Barandela}, Fernando and {Mart{\'\i}n-Gonz{\'a}lez}, Diego}, title = {{A possible pathway to UHZ1-type systems at z {\ensuremath{\sim}} 10 by heterogeneous mass primordial black holes as dark matter}}, journal = {\mnras}, keywords = {quasars: supermassive black holes, cosmology: miscellaneous, cosmology: observations, diffuse radiation, early Universe}, year = {2026}, month = mar, volume = {546}, number = {3}, eid = {stag124}, pages = {stag124}, doi = {10.1093/mnras/stag124}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.546ag124K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, exotic physics, heavy seed, jwst, theory}, eprint = {2601.08936}, archiveprefix = {arXiv}, primaryclass = {astro-ph.CO}, month_numeric = {3} }

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Toward Black Hole Stars: Supermassive Black Hole Growth in Nuclear Clusters via Stellar-object and Gas Accretion

Konstantinos Kritos and Joseph Silk

The Astrophysical Journal Letters, Mar 2026

Abs DOI ADS arXiv

Supermassive black hole (SMBH) growth plausibly occurs via runaway astrophysical black hole mergers in nuclear star clusters that form intermediate mass black hole seeds at high redshifts. Such a model yields an order-of-magnitude higher rate of tidal disruption events than that of compact-object captures. Our prediction, normalized to our proposed resolution of SMBH seeding, yields detectable tidal disruption event rates at high redshift. The resulting dense gas cocoons generate compact galactic nuclei, each incorporating a central, massive, black hole star, with comparable masses in gas, stars, and massive black holes within a scale of around a parsec as inferred from the various Little Red Dot spectral signatures.

@article{2026ApJ..1000L..21K, author = {{Kritos}, Konstantinos and {Silk}, Joseph}, title = {{Toward Black Hole Stars: Supermassive Black Hole Growth in Nuclear Clusters via Stellar-object and Gas Accretion}}, journal = {\apjl}, keywords = {Stellar dynamics, Gravitational wave sources, Transient sources, 1596, 677, 1851}, year = {2026}, month = mar, volume = {1000}, number = {1}, eid = {L21}, pages = {L21}, doi = {10.3847/2041-8213/ae4c52}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1000L..21K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, heavy seed, super-eddington, theory}, eprint = {2602.15929}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, month_numeric = {3} }

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Constraints on dynamically formed massive black holes in little red dots from X-ray non-detections

M. Liempi, D. R. G. Schleicher, M. A. Latif, and 4 more authors

Astronomy & Astrophysics, Mar 2026

Abs DOI ADS arXiv

The existence of extremely massive and compact galaxies, also called little red dots (LRDs), at z \ensuremath≳ 2 challenges models of early structure formation, suggesting extremely rapid stellar and black hole (BH) assembly. These galaxies are efficient environments for rapid BH growth, but several LRDs show no evidence of strong emission from the active galactic nuclei in X-rays. Our work uses a subsample of X-ray non- detected LRDs to determine whether the collision-based BH formation scenario is compatible with the non-detections and to constrain the physical parameters (e.g., metallicity) and observational parameters (e.g., column density). Our results show that LRDs might be ideal birthplaces for the formation of massive BHs, particularly in the case of a mass-radius relation R gal \ensuremath∝ M gal 0.6 (similar to spiral galaxies in the local Universe). Given the high stellar densities, collision-based models suggest seed masses greater than those observed in the local Universe, and these are compatible with the mass-radius relation of high-redshift BHs. We modeled the BH seed formation and subsequent X-ray emission to investigate the physical and observational parameter space to compare with the observed X-ray upper limits in the soft (0.3 \ensuremath- 2 keV) and hard band (2 \ensuremath- 7 keV). We found that exponents in the mass-radius relation above 0.55 favor the collision-based scenario, but consistency with the stacked X-ray analysis requires specific combinations of accretion and obscuration parameters. Additionally, we found that constant or increasing star formation rate scenarios assuming high Eddington ratios and long duty cycles are feasible, but require higher column densities and/or a higher level of metal enrichment in the shielding columns. Alternatively, moderate sub-Eddington accretion rates seem to be sufficient to reconcile the massive seeds with their final observed masses, consistent with the observed X-ray weakness. Overall, we conclude that even if LRDs were initially starburst galaxies, they should evolve into an active galactic nucleus.

@article{2026A&A...708A..44L, author = {{Liempi}, M. and {Schleicher}, D. R. G. and {Latif}, M. A. and {Schneider}, R. and {Flammini Dotti}, F. and {Escala}, A. and {Vergara}, M. C.}, title = {{Constraints on dynamically formed massive black holes in little red dots from X-ray non-detections}}, journal = {\aap}, keywords = {galaxies: evolution, galaxies: formation, galaxies: high-redshift, galaxies: nuclei, quasars: supermassive black holes, X-rays: galaxies}, year = {2026}, month = mar, volume = {708}, eid = {A44}, pages = {A44}, doi = {10.1051/0004-6361/202558108}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...708A..44L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {heavy seed, non-agn, obscuration, theory, x-ray}, eprint = {2602.21002}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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Synthetic Spectral Library of Optically Thick Atmospheres for Little Red Dots

Hanpu Liu, Yan-Fei Jiang, Eliot Quataert, and 3 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

Little Red Dots (LRDs) challenge conventional models of active galactic nuclei. At rest-optical-to-near-infrared (IR) wavelengths, these compact extragalactic objects show blackbody-like continuum emission and spectral features reminiscent of stars, motivating models with an optically thick atmosphere at T_\rm\! eff\sim4000-5000\rm~K. We develop (and publicly release) a synthetic spectral library of optically thick atmospheres with gas conditions tailored for LRDs, parameterized by effective temperature T_\rm\! eff and surface gravity g. Given the uncertain dynamical structure of LRDs, we interpret g most directly as a photospheric density ρ_\rm\! ph. We show that blackbodies are only crude approximations to the emission from LRD-like atmospheres. Spectral features are abundant, many of which are sensitive diagnostics of photospheric density, including the overall curvature of the spectral energy distribution, the rest-1.6\rm~μm spectral “kink” from \rm H^- opacity, and the Ca II triplet (CaT) absorption at rest-8500 \unicodex212B. When compared against a local LRD, \textbackslashegg, all three features consistently indicate a low photospheric density of ρ_\rm\! ph∼10^-11\rm~g~cm^-3 (g\sim10^-3\rm~cm~s^-2 in our library). This disfavors hydrostatic configurations and suggests a mass within the photosphere (black hole plus gas) of 10^4~M_⊙, with an Eddington ratio λ_\rm Eddrsim20, if the CaT width traces turbulent support at the photosphere in spherical symmetry; the inferred mass could be higher depending on the geometry and the radius probed by CaT. For higher redshift LRDs, we advocate for rest-near-IR spectroscopic surveys and high-resolution spectra of potential absorption lines as a test of the optically thick atmosphere scenario and as a unique probe of the central engine mass.

@article{2026arXiv260302317L, author = {{Liu}, Hanpu and {Jiang}, Yan-Fei and {Quataert}, Eliot and {Greene}, Jenny E. and {Ma}, Yilun and {Lin}, Xiaojing}, title = {{Synthetic Spectral Library of Optically Thick Atmospheres for Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics}, year = {2026}, month = mar, eid = {arXiv:2603.02317}, pages = {arXiv:2603.02317}, archiveprefix = {arXiv}, eprint = {2603.02317}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260302317L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, black hole mass, sed, spectroscopy, theory}, month_numeric = {3} }

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The Engine and its Flows: Little Red Dot spectra are shaped by the column densities of their gas envelopes

Jorryt Matthee, Alberto Torralba, Gabriele Pezzulli, and 23 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

JWST data have enabled the abundant identification of compact broad Balmer line sources nicknamed the Little Red Dots. While they share broad lines with active galactic nuclei, they are unusually X-ray and infrared weak. We investigate the origin of the Balmer line profiles based on an empirical analysis of 18 broad Hα-selected sources with high quality spectra at z\approx3-7. The Hα line profiles vary systematically with Balmer break strength: sources with blue UV to optical colors show a narrow core profile, redder sources with Balmer breaks a blue shifted absorption (P Cygni shape), and the reddest sources display absorption-dominated cores. All Hα lines have symmetric exponential wings, which are more dominant and slightly broader in red sources. Balmer absorption is present in \sim60 % of the sample, with Hβ showing relatively stronger absorption. Drawing upon empirical analogies with stellar phenomena, we interpret these trends as being due to radiative processes that depend on variations in the optical depth, ionisation state and column density of a clumpy, partially ionised envelope. We unveil a correlation between the absorber velocity and Balmer break strength, with the densest absorbers inflowing and bluer sources having faster outflows. This indicates viewing angle or evolutionary effects where optically thick gas is inflowing, as suggested in models of super- Eddington accretion, and the engine can more easily drive outflows in directions with lower column densities. This new understanding of Balmer line profiles as tracing gas properties rather than dynamical broadening helps resolve tensions associated with high inferred black hole masses from standard virial calibrations, and reveals the complex gas environment around the hot central engine.

@article{2026arXiv260317667M, author = {{Matthee}, Jorryt and {Torralba}, Alberto and {Pezzulli}, Gabriele and {Naidu}, Rohan P. and {Chisholm}, John and {Mascia}, Sara and {Greene}, Jenny E. and {Ishikawa}, Yuzo and {Gronke}, Max and {Wuyts}, Stijn and {Bordoloi}, Rongmon and {Brammer}, Gabriel and {Chang}, Seok-Jun and {Eilers}, Anna-Christina and {de Graaff}, Anna and {Hviding}, Raphael E. and {Iani}, Edoardo and {Illingworth}, Garth and {Kashino}, Daichi and {Labbe}, Ivo and {Ma}, Yilun and {Maseda}, Michael V. and {Meyer}, Romain and {Nelson}, Erica and {Oesch}, Pascal and {Xiao}, Mengyuan}, title = {{The Engine and its Flows: Little Red Dot spectra are shaped by the column densities of their gas envelopes}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = mar, eid = {arXiv:2603.17667}, pages = {arXiv:2603.17667}, archiveprefix = {arXiv}, eprint = {2603.17667}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260317667M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, jwst, obscuration, spectroscopy, super-eddington}, month_numeric = {3} }

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Constraints on the host galaxy and AGN properties of three z > 6 JWST AGN from NOEMA observations

Giovanni Mazzolari, Hannah Übler, Rodrigo Herrera Camus, and 32 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

We targeted with deep NOEMA observations the [CII]158μm emission of three JWST-discovered AGN at z>6. Two of them have the typical features of Little Red Dots (LRDs), while the third one is a blue, extended, Type I AGN. We do not significantly detect [CII] emission or dust continuum in any of the targets, even after stacking. The resulting [CII] luminosity upper limits, \log (L_[CII]/L_⊙)<7.77-8.1, lie \sim2σ below the values expected from the [CII]-SFR relation, and we explore different scenarios to explain the lack of [CII]. We obtained upper limits on the gas masses of \log (M_gas/M_⊙)<9.26-9.59 corresponding to \log( M_dust/M_⊙)<5.68-6.55 assuming a metallicity dependent dust to gas ratio. Using the continuum non-detections (rms ∼16-25 ~μJy) together with JWST/MIRI constraints, we performed a revised SED-fitting decomposition, resulting in stellar masses up to ∼2 dex lower than previously reported, and implying 0.03≲M_BH/M_*\lesssim0.7. For the two LRDs, the SED is well reproduced by stellar emission in the rest-frame UV, while the rising rest-frame optical slope, flattening toward the near- infrared, is consistent with emission from a Type I AGN partially obscured along the polar direction with E(B-V)_\rm polar≃1, in agreement with attenuation derived from the broad lines Balmer decrement. This decomposition demonstrates that a relatively standard AGN configuration can reproduce the SEDs of the two LRDs, without invoking more exotic scenarios. Finally, we investigate the positions of the three sources in the IRX-β_UV plane, finding that they lie in a parameter space where galaxies are typically characterized by patchy dust distributions. Our analysis highlights the importance of millimeter constraints to characterize the different physical properties of high-z AGN.

@article{2026arXiv260329652M, author = {{Mazzolari}, Giovanni and {{\"U}bler}, Hannah and {Herrera Camus}, Rodrigo and {Davies}, Ric and {Tacconi}, Linda and {Lutz}, Dieter and {F{\"o}rster Schreiber}, Natascha and {D'Eugenio}, Francesco and {Lee}, Minju and {Barfety}, Capucine and {Bertola}, Elena and {Bunker}, Andrew and {Burkert}, Andreas and {Chen}, Jianhang and {Cresci}, Giovanni and {Eisenhauer}, Frank and {Espejo Salcedo}, Juan Manuel and {Flesch}, Simon and {Genzel}, Reinhard and {Ji}, Xihan and {Lee}, Lilian and {Liu}, Daizhong and {Marconcini}, Cosimo and {Maiolino}, Roberto and {Naab}, Thorsten and {Nestor Shachar}, Amit and {Pannikkote}, Meghana and {Parlanti}, Eleonora and {Pastras}, Stavros and {Perna}, Michele and {Pulsoni}, Claudia and {Rodriguez del Pino}, Bruno and {Sturm}, Eckhard and {Shimizu}, Taro and {Tozzi}, Giulia}, title = {{Constraints on the host galaxy and AGN properties of three z > 6 JWST AGN from NOEMA observations}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2026}, month = mar, eid = {arXiv:2603.29652}, pages = {arXiv:2603.29652}, archiveprefix = {arXiv}, eprint = {2603.29652}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260329652M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, host galaxy, jwst, obscuration, sed}, month_numeric = {3} }

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Counting Little Red Dots at z < 4 with Ground-based Surveys and Spectroscopic Follow-up

Yilun Ma, Jenny E. Greene, David J. Setton, and 13 more authors

The Astrophysical Journal, Mar 2026

Abs DOI ADS arXiv

Little red dots (LRDs) are a population of red, compact objects discovered by JWST at z > 4. At 4 4 to \ensuremath∼10^\ensuremath-5.3 cMpc^\ensuremath-3 at 2.7 < z < 3.7 and \ensuremath∼10^\ensuremath-5.7 cMpc^\ensuremath-3 at 1.7 < z < 2.7. We also present the Magellan/FIRE spectrum of our first followed-up candidate, DEEP23-z2LRD1 at z_spec = 2.26, as a proof of concept for our sample selection. Similar to high-redshift LRDs, the spectrum of DEEP23-z2LRD1 exhibits broad H\ensuremathα emission with FWHM ≍ 2400 km s^\ensuremath-1 and with nearly symmetric narrow H\ensuremathα absorption. Additionally, DEEP23-z2LRD1 has extremely narrow [O III] lines with FWHM ≍ 140 km s^\ensuremath-1, suggesting the presence of an accreting black hole in a low-mass host galaxy. Limited by the angular resolution of ground-based surveys, we emphasize that spectroscopic follow-ups are required to characterize the contamination fraction of this sample and pin down LRD number density at z < 4.

@article{2026ApJ..1000...59M, author = {{Ma}, Yilun and {Greene}, Jenny E. and {Setton}, David J. and {Goulding}, Andy D. and {Annunziatella}, Marianna and {Fan}, Xiaohui and {Kokorev}, Vasily and {Labbe}, Ivo and {Li}, Jiaxuan and {Lin}, Xiaojing and {Marchesini}, Danilo and {Matthee}, Jorryt and {Robbins}, Luke and {Sajina}, Anna and {Sawicki}, Marcin and {Telford}, O. Grace}, title = {{Counting Little Red Dots at z < 4 with Ground-based Surveys and Spectroscopic Follow-up}}, journal = {\apj}, keywords = {Active galactic nuclei, Black holes, Galaxy formation, High-redshift galaxies, 16, 162, 595, 734}, year = {2026}, month = mar, volume = {1000}, number = {1}, eid = {59}, pages = {59}, doi = {10.3847/1538-4357/ae4596}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1000...59M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, emission lines, non-jwst, sample selection, spectroscopy}, eprint = {2504.08032}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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The rise and fall of little red dots could be driven by the environment

Rosa M. Mérida, Gaia Gaspar, Yoshihisa Asada, and 9 more authors

Astronomy & Astrophysics, Mar 2026

Abs DOI ADS arXiv

The little red dot (LRD) paradigm comprises three main unknowns that are intrinsically connected: (1) What is the nature of these sources? (2) How do they form? (3) How do they evolve? Larger spectroscopic samples and high-resolution data are needed to delve deeper into the mechanisms governing these sources. Understanding their formation and evolution requires identifying the rise and fall of the key features that characterize these systems, such as their compactness and “V”-shaped spectral energy distributions. In this work, we present a galaxy system nicknamed “The Stingray” that was identified in the Canadian NIRISS Unbiased Cluster Survey (CANUCS). This group contains three sources at z_spec = 5.12, including an active galactic nucleus (AGN), a Balmer break galaxy, and a star-forming satellite. The latter resembles a building blocks system in which interactions boost stellar mass and black hole mass growth beyond what is expected from secular processes alone. The AGN in this system exhibits features indicative of a transitional object, bridging a normal AGN and an LRD phase. These features include a blue rest-frame UV slope, compact size, and a broad H\ensuremathα line (all of which are characteristic of LRDs), but a flatter rest-frame optical slope compared to that observed in LRDs. The features in this source point to the emergence or fading of an LRD, potentially triggered by environmental effects.

@article{2026A&A...707A.212M, author = {{M{\'e}rida}, Rosa M. and {Gaspar}, Gaia and {Asada}, Yoshihisa and {Sawicki}, Marcin and {Christopher Omori}, Kiyoaki and {Willott}, Chris J. and {Martis}, Nicholas S. and {Muzzin}, Adam and {Noirot}, Ga{\"e}l and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Sarrouh}, Ghassan T. E. and {Tripodi}, Roberta}, title = {{The rise and fall of little red dots could be driven by the environment}}, journal = {\aap}, keywords = {galaxies: active, galaxies: evolution, galaxies: high-redshift, galaxies: interactions}, year = {2026}, month = mar, volume = {707}, eid = {A212}, pages = {A212}, doi = {10.1051/0004-6361/202557594}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...707A.212M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, morphology, sed, spectroscopy}, eprint = {2510.06408}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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A Unified Explanation for JWST Little Red Dots and High-Redshift Low-Mass Disk-like Galaxies: Prolate Galaxies Viewed End-on vs Side-on

Yingjie Peng

arXiv e-prints, Mar 2026

Abs ADS arXiv

Recent JWST surveys have revealed two puzzling high-redshift phenomena: (1) an unexpectedly large abundance of flattened, disk-like galaxies at z > 3, and (2) a rare population of compact, extremely red sources at z \raisebox-0.5ex~4-9 (“Little Red Dots,” LRDs) that often show V-shaped SEDs and very broad Balmer lines. These findings lack a consensus interpretation and have motivated models ranging from dusty starbursts to obscured AGN and more exotic scenarios. We propose that both phenomena are linked by a simple geometric consequence of a third clue: mounting evidence from structural modeling and axis-ratio statistics indicates that many low-mass galaxies at z > 3 are intrinsically prolate (cigar-like), not oblate rotation- supported disks. In this picture, a substantial fraction of the flattened, disk-like morphologies reported at z > 3 arise from side-on and intermediate-angle projections of prolate systems, while the rare near end-on views appear extremely compact and high-surface-brightness, and are preferentially reddened by the maximal line-of-sight column, naturally matching key elements of LRD selection. The expected fraction of near end-on systems, P_\textend = 1 - \cos(θ_\textmax), is \raisebox-0.5ex\textasciitilde1-3% for θ_\textmax \raisebox-0.5ex~10\textdegree-15\textdegree, consistent with LRD demographics in wide JWST fields. This orientation-based framework does not exclude AGN or starburst activity; rather, it explains LRD rarity as an orientation effect and provides a natural route to the large columns of gas/dust and scattering depths inferred in recent dense-gas and electron-scattering interpretations of LRD spectra, without fine-tuned new physics. The model makes falsifiable predictions to validate or rule out this geometric interpretation.

@article{2026arXiv260301668P, author = {{Peng}, Yingjie}, title = {{A Unified Explanation for JWST Little Red Dots and High-Redshift Low-Mass Disk-like Galaxies: Prolate Galaxies Viewed End-on vs Side-on}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = mar, eid = {arXiv:2603.01668}, pages = {arXiv:2603.01668}, archiveprefix = {arXiv}, eprint = {2603.01668}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260301668P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, morphology, obscuration, sed, theory}, month_numeric = {3} }

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Radio detection of a local little red dot

L. F. Rodriguez and I. F. Mirabel

Astronomy & Astrophysics, Mar 2026

Abs DOI ADS arXiv

Context. One of the most important discoveries by the James Webb Space Telescope (JWST) is the unexpected existence of very large quantities of so-called little red dots (LRDs) in the early Universe (z > 4). These are compact luminous red galaxies with intriguing physical properties, one of which is the absence of radio detections. Aims. We wish to know if LRDs give off radio emission produced by accreting intermediate-mass or supermassive black holes (IMBHs or SMBHs) or by frequent supernovae from a cluster of massive stars. Methods. Assuming that LRDs at high redshifts have not been detected at radio wavelengths because they reside at large distances and/or the observational capabilities are limited, we present images made from archive Very Large Array (VLA) radio observations of J1047+0739 and J1025+1402. These are two analog candidate LRDs in the Local Universe at redshifts z = 0.1\ensuremath-0.2. Results. The source J1047+0739 at z = 0.1682 is detected at 6.0 GHz in 2018 with the VLA-A as a compact source with a radius smaller than 0.2 arcsec (< 700 pc at d ≃ 750 Mpc). Its flux density was 117 \ensuremath\pm 8 \ensuremathμJy and its in-band spectral index was \ensuremath-0.85 \ensuremath\pm 0.24, which is typical of optically thin synchrotron emission. It was also detected at 5.0 GHz in 2010 with the VLA-C, showing a flux density of 130 \ensuremath\pm 9 \ensuremathμJy. We also detect a compact source very near J1025+1402 (≃2″) with a flux density of 45 \ensuremath\pm 10 \ensuremathμJy that might be tracing a kiloparsec-scale jet emanating from an IMBH or SMBH. Conclusions. The observed flux densities can be provided by either a radio luminous supernova or an accreting IMBH or SMBH. However, the lack of significant variation in the flux density over eight years favors the IMBH─SMBH hypothesis. Radio time monitoring of this and other Local Little Red Dots (LLRDs) might help us solve the mystery of the radio silence of its cosmological counterparts.

@article{2026A&A...707L..17R, author = {{Rodriguez}, L. F. and {Mirabel}, I. F.}, title = {{Radio detection of a local little red dot}}, journal = {\aap}, keywords = {supernovae: general, galaxies: jets, galaxies: nuclei}, year = {2026}, month = mar, volume = {707}, eid = {L17}, pages = {L17}, doi = {10.1051/0004-6361/202558326}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...707L..17R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, local counterpart, non-agn, radio, variability}, eprint = {2512.03331}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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A quasi-star is born: formation and evolution of accreting quasi-stars as a metallicity-independent pathway to Little Red Dots

J. Roman-Garza, D. Schaerer, C. Charbonnel, and 5 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

To investigate the rest-frame optical emission of “Little Red Dots”, we model the formation of and evolution of quasi-stars, i.e. stellar envelopes supported by the accretion luminosity onto a central black hole, originating from rapidly accreting proto- stars reaching the supermassive star regime (>10^4 M_⊙) and undergoing general relativistic instability. We compute stellar evolution models with net mass gain rates =0.01, 0.1, and 1 M_⊙/yr and metallicities Z=0-0.01. For the mass gain rates \ge 0.1 M_⊙/yr, stars remain nearly fully convective with T_\mathrmeff\sim4000-9000\raisebox-0.5ex\textasciitildeK. The general relativistic instability leading to central BH formation occurs at M_⋆\sim3.5\times10^4 M_⊙ (6.6\times10^4 M_⊙) for \dotM_\rm acc=0.1 M_⊙/yr (1 M_⊙/yr), at luminosities L ∼10^9 L_⊙. The lifetime of quasi-stars is estimated to be 10^7-10^8\raisebox-0.5ex\textasciitildeyr, \sim100-1000 times longer than their progenitors. In an environment allowing for rapid accretion the formation, evolution, and properties of quasi-stars are found be essentially independent of metallicity. Comparing the luminosities of our models with those of Little Red Dots at z<4.5 (L_\mathrmbol\sim10^9.5-10^11.5 L_⊙) yields quasi-star masses 10^4.5-10^6.5 M_⊙. The observed minimum luminosity of \sim10^9.5åisebox-0.5ex~\textbackslashLsun\implies accretion rates rsim0.1 M_⊙/yr for Little Red Dots progenitors. Our models offer a metallicity-independent framework supporting quasi-stars as the source of Little Red Dot optical emission, and provide insights into their lifetimes, composition, and progenitor environment.

@article{2026arXiv260321714R, author = {{Roman-Garza}, J. and {Schaerer}, D. and {Charbonnel}, C. and {Fragos}, T. and {Cenci}, E. and {Marques-Chaves}, R. and {Oesch}, P. and {Xiao}, M.}, title = {{A quasi-star is born: formation and evolution of accreting quasi-stars as a metallicity-independent pathway to Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Solar and Stellar Astrophysics, Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = mar, eid = {arXiv:2603.21714}, pages = {arXiv:2603.21714}, archiveprefix = {arXiv}, eprint = {2603.21714}, primaryclass = {astro-ph.SR}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260321714R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, exotic physics, simulation, super-eddington, theory}, month_numeric = {3} }

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Islands of Electromagnetic Tranquility in Our Galactic Core and Little Red Dots that Shelter Molecules and Prebiotic Chemistry

R. Ruffini and Yu Wang

The Astrophysical Journal Letters, Mar 2026

Abs DOI ADS arXiv

Both the Galactic center and little red dots (LRDs) host million-solar- mass black holes within dense, cold reservoirs of molecules associated with dust grains, and are electromagnetically tranquil. These conditions enable complex molecular chemistry and may serve as natural laboratories for prebiotic genetic evolution by allowing the synthesis of organic molecules essential for life.

@article{2026ApJ..1000L..11R, author = {{Ruffini}, R. and {Wang}, Yu}, title = {{Islands of Electromagnetic Tranquility in Our Galactic Core and Little Red Dots that Shelter Molecules and Prebiotic Chemistry}}, journal = {\apjl}, keywords = {Galaxy evolution, Astrobiology, Cosmology, 594, 74, 343}, year = {2026}, month = mar, volume = {1000}, number = {1}, eid = {L11}, pages = {L11}, doi = {10.3847/2041-8213/ae3a76}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1000L..11R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust-reddened, non-agn, obscuration}, eprint = {2509.17484}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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Little Red and Blue Dots: simply stratified Broad Line Regions

J. Scholtz, F. D’Eugenio, R. Maiolino, and 14 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

It has been claimed that a fraction of the so-called Little Red Dots (LRDs) are characterised by exponential broad line profiles, which have been ascribed to broadening from electron scattering by an ionised cocoon. In this work, we investigate the Hα broad line profiles of 32 AGN, including Little Red Dots (LRDs), Little Blue Dots (LBDs), and X-ray detected sources, using high SNR and resolution spectroscopy. We find that while single Gaussian models are statistically rejected, the exponential model is not universally preferred. Lorentzian and multi- Gaussian profiles provide equally good or superior fits for the majority of the sample, with no statistical preference for exponential profiles in \sim60% of cases across all AGN subtypes. There are indications that exponential profiles are preferred more frequently among LBDs, indicating that exponential profiles are not a prerogative of LRDs, which actually seem to more often favour Lorentzian profiles. Furthermore, we demonstrate that exponential wings can emerge naturally from the stratification of BLR clouds in virial motion, without invoking any scattering process. More generally, we also show that stacking multiple broad lines (either from multiple objects, as done in previous works, or from different BLR components within the same object) generally yields an exponential profile, even if none of the individual profiles are exponential. Explaining the exponential profiles in terms of BLR stratification solves various observational tensions with the electron scattering interpretation. While electron scattering may play a role, there is no evidence that it dominates the line profiles and that it significantly affects the inferred black hole masses.

@article{2026arXiv260322277S, author = {{Scholtz}, J. and {D'Eugenio}, F. and {Maiolino}, R. and {Brazzini}, M. and {{\"U}bler}, H. and {Ji}, X. and {Perna}, M. and {Sun}, F. and {Brocchi}, G. and {Carniani}, S. and {Cresci}, G. and {Ivey}, L. R. and {Juod{\v{z}}balis}, I. and {Marconi}, A. and {Mazzolari}, G. and {Risaliti}, G. and {Trefoloni}, B.}, title = {{Little Red and Blue Dots: simply stratified Broad Line Regions}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = mar, eid = {arXiv:2603.22277}, pages = {arXiv:2603.22277}, archiveprefix = {arXiv}, eprint = {2603.22277}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260322277S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, emission lines, kinematics, spectroscopy}, month_numeric = {3} }

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The rest-ultraviolet to infrared spectral energy distributions of heavily reddened quasars are ’V-shaped’ and hot-dust poor

Matthew Stepney, Manda Banerji, Shenli Tang, and 2 more authors

Monthly Notices of the Royal Astronomical Society, Mar 2026

Abs DOI ADS arXiv

We present a rest-ultraviolet to infrared spectral energy distribution (SED) analysis of 63 heavily reddened quasars (HRQs) at redshifts and with dust extinctions . Our analysis demonstrates that SEDs with red optical and blue ultraviolet (UV) continua are very common in HRQs, with 82 per cent of the sample showing a UV-excess relative to the reddened quasar continuum. We model the SEDs by combining a reddened quasar and an unobscured scattered light component, though contributions from a star- forming host galaxy cannot be ruled out. The average scattering fraction is small (0.3 per cent). Higher scattering fractions are ruled out by the colour-cut used to select HRQs, which pre- dates the discovery of the James Webb Space Telescope ’Little Red Dot’ (LRD) population. Hence, LRDs generally have bluer UV continua. Nevertheless, four HRQs satisfy the LRD UV/optical continuum slope selections and are therefore massive cosmic noon analogues of LRDs. Analysis of the near-infrared SEDs of HRQs reveals a deficit of hot dust relative to blue quasars, similar to what is observed in LRDs. This suggests HRQs trace a phase where strong active galactic nucleus feedback processes eject dust from the inner torus. The UV scattering fraction of HRQs is weakly correlated with the amount of hot dust emission and anticorrelated with the line-of-sight extinction, . This is consistent with the hot dust acting as the scattering medium, and the line-of-sight extinction being dominated by dust on interstellar medium scales in the host galaxy.

@article{2026MNRAS.546ag191S, author = {{Stepney}, Matthew and {Banerji}, Manda and {Tang}, Shenli and {Temple}, Matthew J. and {Hewett}, Paul C.}, title = {{The rest-ultraviolet to infrared spectral energy distributions of heavily reddened quasars are 'V-shaped' and hot-dust poor}}, journal = {\mnras}, keywords = {galaxies: evolution, galaxies: photometry, quasars: general}, year = {2026}, month = mar, volume = {546}, number = {4}, eid = {stag191}, pages = {stag191}, doi = {10.1093/mnras/stag191}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.546ag191S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, dust-reddened, multi-wavelength, obscuration, sed}, eprint = {2601.17416}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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A Black Hole Envelope Interpretation for Cosmological Demographics of Little Red Dots

Hiroya Umeda, Kohei Inayoshi, Yuichi Harikane, and 1 more author

The Astrophysical Journal, Mar 2026

Abs DOI ADS arXiv

Little Red Dots (LRDs) newly discovered with JWST are active galactic nuclei (AGNs) that may represent black hole (BH) growth at the earliest cosmic epochs. These sources show puzzling features unlike typical AGNs, including red optical continua, weak hot- dust emission, and a lack of detectable X-rays. Previously, LRDs have often been interpreted as dust-reddened AGNs, leading to severe inconsistencies with the luminosity and BH mass densities inferred for previously known AGNs over 0 < z < 5. The BH envelope (BHE) model has been proposed to explain these characteristics, in which an accreting BH is enshrouded by a dense, optically thick gaseous envelope. In this article, we reanalyze the spectral energy distributions of \ensuremath∼400 photometric LRDs in the COSMOS-Web survey using the BHE model and reassess their implications for cosmological BH evolution. We find that the optical─near-IR spectra of LRDs are well reproduced by blackbody emission with an effective temperature of 4000─6000 K. Within the BHE framework, the inferred bolometric luminosities decrease by \ensuremath≳1─2 orders of magnitude compared to assumptions for dust-reddened AGNs. As a result, the revised luminosity function, BH accretion density, and BH mass function become consistent with those of AGNs at z < 5. The stellar masses of LRD hosts are estimated by attributing the UV excesses to star formation. Although the resulting M_BH/M_\ensuremath⋆ ratio remains higher than the local empirical value, the excess is modest. Overall, the BHE model not only resolves the spectral features of LRDs but also brings their statistical properties into agreement with the broader cosmological BH population.

@article{2026ApJ...999..183U, author = {{Umeda}, Hiroya and {Inayoshi}, Kohei and {Harikane}, Yuichi and {Murase}, Kohta}, title = {{A Black Hole Envelope Interpretation for Cosmological Demographics of Little Red Dots}}, journal = {\apj}, keywords = {Supermassive black holes, Galaxy formation, Active galactic nuclei, 1663, 595, 16}, year = {2026}, month = mar, volume = {999}, number = {2}, eid = {183}, pages = {183}, doi = {10.3847/1538-4357/ae4101}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...999..183U}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, agn-dominated, black hole mass, jwst, sed}, eprint = {2512.04208}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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Halo assembly bias in the early Universe: a clustering probe of the origin of the Little Red Dots

Zihao Wang, Fangzhou Jiang, Haonan Zheng, and 5 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

The clustering of galaxies encodes key information about the structure and assembly history of their host dark matter (DM) haloes, providing a powerful probe of the origin of extreme high- redshift systems. While halo assembly bias has been extensively studied at low redshift, its behavior in the early Universe remains poorly explored. Using the large-volume, high-resolution Shin-Uchuu cosmological N-body simulation, we characterize halo assembly bias associated with formation time, concentration, and angular momentum across a wide range of halo masses and redshifts. We find that the sign and amplitude of assembly bias depend on halo mass for both concentration and spin. High-concentration and low-spin haloes are more strongly clustered below characteristic peak heights of ν∼1.5 and ∼0.75, respectively, while the trends weaken or reverse at higher masses. Halo age bias persists at all redshifts but decreases toward higher masses and earlier cosmic times. We apply these results to assess whether clustering can distinguish competing formation scenarios for the Little Red Dots (LRDs). We find that the direct-collapse-black-hole (DCBH) scenario predicts the strongest large-scale bias and enhanced pair fractions, the self-interacting-dark-matter (SIDM) core-collapse scenario and low-spin compact-galaxy scenarios yield weaker clustering due to lower characteristic halo masses and spin- related secondary bias, and a primordial-black-hole (PBH) scenario predicts unbiased clustering. Our results demonstrate that halo assembly bias and characteristic host masses provide powerful diagnostics for constraining the physical origin of LRDs, offering testable predictions for upcoming clustering measurements with JWST and future deep surveys.

@article{2026arXiv260315736W, author = {{Wang}, Zihao and {Jiang}, Fangzhou and {Zheng}, Haonan and {Shen}, Xuejian and {Jia}, Zixiang and {Ho}, Luis C. and {Inayoshi}, Kohei and {Jiang}, Linhua}, title = {{Halo assembly bias in the early Universe: a clustering probe of the origin of the Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = mar, eid = {arXiv:2603.15736}, pages = {arXiv:2603.15736}, archiveprefix = {arXiv}, eprint = {2603.15736}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260315736W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {clustering, early universe, exotic physics, heavy seed, simulation}, month_numeric = {3} }

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A cosmological framework for stellar collisions at high redshift in proto-globular clusters, nuclear star clusters, and Little Red Dots

Claire E. Williams, Smadar Naoz, Sanaea C. Rose, and 8 more authors

arXiv e-prints, Mar 2026

Abs ADS arXiv

Observations and cosmological simulations indicate that the early Universe hosted numerous compact, high-density stellar systems, where close encounters and physical collisions between stars were likely common. We develop a bottom-up framework for stellar dynamics in such environments, spanning systems with and without intermediate- and supermassive black holes, and covering regimes where stellar collisions may or may not dominate the evolution. This radially-resolved analytic model connects dense star clusters in their cosmological context to observable outcomes mediated by stellar collisions. Initial conditions and environmental properties are drawn from high-resolution cosmological simulations, enabling exploration across a broad region of parameter space. The analytic predictions are validated against Monte Carlo simulations, demonstrating good agreement across key regimes. We find that stellar collisions are ubiquitous in many high-redshift environments, with runaway sequences naturally leading to the formation of very massive stars at early times. Finally, we show that high rates of destructive collisions can rapidly build up extremely dense gaseous environments around massive black holes, potentially providing an analogue to the observed population of Little Red Dots.

@article{2026arXiv260326872W, author = {{Williams}, Claire E. and {Naoz}, Smadar and {Rose}, Sanaea C. and {Burkhart}, Blakesley and {Yoshida}, Naoki and {Chen}, Avi and {Kremer}, Kyle and {Lake}, William and {Marinacci}, Federico and {Menon}, Shyam H. and {Vogelsberger}, Mark}, title = {{A cosmological framework for stellar collisions at high redshift in proto-globular clusters, nuclear star clusters, and Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = mar, eid = {arXiv:2603.26872}, pages = {arXiv:2603.26872}, archiveprefix = {arXiv}, eprint = {2603.26872}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260326872W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, simulation, starburst, theory}, month_numeric = {3} }

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Research Progress on the Discovery of “Little Red Dots” in the Early Universe by JWST

Luyu Wu and Jiasheng Huang

Progress in Astronomy, Mar 2026

Abs DOI ADS

Spectroscopy with the James Webb Space Telescope (JWST) has revealed a sample of compact sources with red colors at rest-frame optical wavelengths, known as Little Red Dots (LRD). The spectral energy distributions (SEDs) of LRDs exhibit a distinct V-shaped structure in the ultraviolet to-optical range and show extreme reddening in the rest-frame infrared. Additionally, some LRDs present broad Balmer emission lines in their spectra, suggesting the possible presence of low-luminosity active galactic nuclei (AGN). However, LRDs exhibit weak X-ray and mid-infrared emission, making it challenging to fully explain their observed properties using traditional AGN models. This review summarizes the latest photo metric and spectroscopic studies of LRDs based on JWST data, systematically outlining their photometric characteristics, spectral properties, and statistical distributions. Furthermore, we discuss the leading physical models proposed for LRDs, including: (1) obscured AGN, where a heavily dust-attenuated low-luminosity AGN dominates the emission; (2) super-Eddington accretion, in which black holes grow at rates exceeding the Eddington limit, influencing the shape of the SED; (3) extreme starburst galaxies, which exhibit intense star formation activity and significant dust attenuation; (4) a composite AGN + starburst model.

@article{2026PrA....44...18W, author = {{Wu}, Luyu and {Huang}, Jiasheng}, title = {{Research Progress on the Discovery of ``Little Red Dots'' in the Early Universe by JWST}}, journal = {Progress in Astronomy}, keywords = {galaxy, AGN, star formation, high redshift, JWST}, year = {2026}, month = mar, volume = {44}, pages = {18-37}, doi = {10.3969/j.issn.1000-8349.2026.01.02}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026PrA....44...18W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, review, sed, spectroscopy, starburst}, month_numeric = {3} }

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Primordial Black Holes as Seeds for Extremely Overmassive Active Galactic Nuclei Observed by JWST

Saiyang Zhang, Boyuan Liu, Volker Bromm, and 1 more author

The Astrophysical Journal Letters, Mar 2026

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has recently identified A2744─QSO1 as a compact, metal-poor, black hole (BH)─dominated galaxy at z ≃ 7. This system exhibits an extreme black-hole-to-stellar mass ratio and unusually low metallicity, posing significant challenges to BH seeding models. Motivated by these discoveries, we perform high-resolution cosmological simulations with a massive primordial black hole (PBH; M_BH = 5 \texttimes 10^7M_\ensuremath⊙) seed, incorporating for the first time a fully coupled treatment of PBH accretion, BH feedback, and Population III/II star formation and stellar feedback. Although PBHs accelerate structure formation through the seed effect, the associated strong thermal feedback from the accretion delays the onset of star formation to z \ensuremath≲ 10, producing short, bursty episodes throughout the subsequent evolution. PBH-driven outflows expel enriched gas from the nucleus, while sustained inflows from the intergalactic medium continuously replenish pristine material. This feedback-regulated cycle naturally yields low accretion rates (ṁBH/ṁedd\ensuremath∼1%\ensuremath-10%), subsolar metallicities (Z/Z_\ensuremath⊙ \ensuremath≲ 10^\ensuremath-2), and extreme M_BH/M_\ensuremath⋆ ratios during both the initial star-forming phase and the subsequent quenching phases, in excellent agreement with JWST observations. Our results demonstrate that massive PBHs offer a viable pathway for forming the most extreme high-redshift systems, providing a physically motivated explanation for the extraordinary properties of A2744─QSO1, as a subclass of the broader population of JWST- discovered “little red dots.”

@article{2026ApJ..1000L..19Z, author = {{Zhang}, Saiyang and {Liu}, Boyuan and {Bromm}, Volker and {K{\"u}hnel}, Florian}, title = {{Primordial Black Holes as Seeds for Extremely Overmassive Active Galactic Nuclei Observed by JWST}}, journal = {\apjl}, keywords = {Dark matter, Early universe, Galaxy formation, Population III stars, Supermassive black holes, 353, 435, 595, 1285, 1663}, year = {2026}, month = mar, volume = {1000}, number = {1}, eid = {L19}, pages = {L19}, doi = {10.3847/2041-8213/ae4bd0}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ..1000L..19Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, heavy seed, jwst, simulation, theory}, eprint = {2512.14066}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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NEXUS: A Spectroscopic Census of Broad-line AGNs and Little Red Dots at 3 \ensuremath≲ z \ensuremath≲ 6

Ming-Yang Zhuang, Junyao Li, Yue Shen, and 5 more authors

The Astrophysical Journal, Mar 2026

Abs DOI ADS arXiv

We present a spectroscopic sample of 24 broad-line AGNs (BLAGNs) at 3 \ensuremath≲ z \ensuremath≲ 6 selected using F322W2+F444W NIRCam/WFSS grism spectroscopy of the central 100 arcmin^2 area of the NEXUS survey. Among these BLAGNs, 15 are classified as Little Red Dots (LRDs) based on their rest- frame UV─optical spectral slopes and compact morphology. The number density of LRDs is \ensuremath∼10^\ensuremath-5 cMpc^\ensuremath-3, with a hint of declining towards lower redshift. These BLAGNs span broad H\ensuremathα luminosities of \ensuremath∼10^42.2─10^43.5 erg s^\ensuremath-1, black hole masses of \ensuremath∼10^6.3─10^8.4 M_\ensuremath⊙, and Eddington ratios of \ensuremath∼0.1─1, though the estimates of black hole mass and Eddington ratio carry large systematic uncertainties. Half of the LRDs show strong Balmer absorption, suggesting high- density gas surrounding the line-emitting region. We detect extended (hundreds of parsecs) rest-frame UV─optical emission from the host galaxy in the majority of these LRDs, which contributes significantly or even dominantly to their total UV emission and largely accounts for the peculiar UV upturn of their spectral energy distribution. We also measure the small- scale (\ensuremath≲1 cMpc) clustering of these BLAGNs and LRDs by cross-correlating with a photometric galaxy sample. Extrapolating the power-law two-point correlation function model to large linear scales, we infer a linear bias of 3.69\ensuremath-2.21+2.78 and typical halo masses of a few \texttimes10^11h^\ensuremath-1 M_\ensuremath⊙ for BLAGNs at the sample median redshift of z \ensuremath∼ 4.5. However, the inferred linear bias and halo masses of LRDs, while formally consistent with those for BLAGNs at \ensuremath∼1.5\ensuremathσ, appear too large to be compatible with their space density, suggesting LRDs may have strong excess clustering on small scales.

@article{2026ApJ...999...31Z, author = {{Zhuang}, Ming-Yang and {Li}, Junyao and {Shen}, Yue and {Lin}, Xiaojing and {Shapley}, Alice E. and {Wang}, Feige and {Wu}, Qiaoya and {Yang}, Qian}, title = {{NEXUS: A Spectroscopic Census of Broad-line AGNs and Little Red Dots at 3 {\ensuremath{\lesssim}} z {\ensuremath{\lesssim}} 6}}, journal = {\apj}, keywords = {Active galactic nuclei, High-redshift galaxies, Supermassive black holes, Clustering, 16, 734, 1663, 1908}, year = {2026}, month = mar, volume = {999}, number = {1}, eid = {31}, pages = {31}, doi = {10.3847/1538-4357/ae3612}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...999...31Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, black hole mass, clustering, emission lines, spectroscopy}, eprint = {2505.20393}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {3} }

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Tentative Detection of Neutral Gas in a Little Red Dot at z = 4.46

Hollis B. Akins, Caitlin M. Casey, John Chisholm, and 7 more authors

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

JWST has revealed a population of broad-line active galactic nuclei at z > 4 with remarkably red colors, so-called “Little Red Dots” (LRDs). Ubiquitous Balmer breaks suggest that they harbor old stellar populations in massive, compact host galaxies. We present Atacama Large Millimeter/submillimeter Array observations of three LRDs at z = 3.10, 4.46, and 7.04, targeting molecular and neutral gas via CO(7─6) and [C I](2─1), respectively. We do not detect CO in any target, placing conservative limits on the host molecular gas mass of \ensuremath≲(1─5) \texttimes 10^10 M_\ensuremath⊙. We report the tentative (\ensuremath∼3.5\ensuremathσ) detection of the [C I](2─1) line in A2744-45924 (z = 4.46), one of the brightest known LRDs. The [C I] line is narrow (FWHM \ensuremath∼ 80 km s^\ensuremath-1), implying a dynamical mass \ensuremath≲10^10 M_\ensuremath⊙, adopting conservative limits for the size of the galaxy. The dynamical mass limit is significantly lower than expected from the local M_BH─M_dyn relation, and is an order of magnitude below the stellar mass derived from spectral energy distribution fitting, potentially supporting a nonstellar origin of the Balmer break. These results, while tentative, paint a picture of LRDs that is markedly different than typical high-z quasars, which live in massive, gas-rich, and actively star- forming host galaxies.

@article{2026ApJ...997..218A, author = {{Akins}, Hollis B. and {Casey}, Caitlin M. and {Chisholm}, John and {Berg}, Danielle A. and {Cooper}, Olivia and {Franco}, Maximilien and {Fujimoto}, Seiji and {Lambrides}, Erini and {Long}, Arianna S. and {McKinney}, Jed}, title = {{Tentative Detection of Neutral Gas in a Little Red Dot at z = 4.46}}, journal = {\apj}, keywords = {AGN host galaxies, Galaxy evolution, High-redshift galaxies, Supermassive black holes, Active galactic nuclei, 2017, 594, 734, 1663, 16}, year = {2026}, month = feb, volume = {997}, number = {2}, eid = {218}, pages = {218}, doi = {10.3847/1538-4357/ae2c77}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...997..218A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, non-agn, spectroscopy}, eprint = {2503.00998}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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HELM’s deep: Highly extincted low-mass galaxies seen by JWST

L. Bisigello, G. Gandolfi, A. Grazian, and 25 more authors

Astronomy & Astrophysics, Feb 2026

Abs DOI ADS arXiv

The dust content of star-forming galaxies is generally positively correlated with their stellar mass. However, some recent James Webb Space Telescope (JWST) studies have shown the existence of a population of dwarf galaxies with an unexpectedly large dust attenuation. Using Cosmic Evolution Early Release Science Survey (CEERS) data, we identified a sample of 1361 highly extincted low-mass (HELM) galaxies, defined as dwarf galaxies (M_* \ensuremath≤ 10^8.5) with A_V > 1 mag or more massive galaxies with an exceptionally high dust attenuation given their stellar mass (i.e. A_V > 1.6 log_10(M_*/ M_\ensuremath⊙)\ensuremath-12.6). The selection was performed using the multi-parameter distribution obtained through a comprehensive spectral energy distribution fitting analysis, based on optical to near-infrared data. After the exclusion of possible contaminants, such as brown dwarfs, little red dots, and high-z (z > 8.5) and ultra-high-z (z > 15) galaxies, the sample mainly includes sources at z < 1, with a tail extending up to z = 7.2. The sample has a median stellar mass of 10^7 M_\ensuremath⊙ and a median dust attenuation of A_V = 2 mag. We analysed the morphology, environment, and star formation rate of these sources to investigate the reason behind their large dust attenuation. In particular, HELM sources have sizes (effective radii, R_e) similar to non-dusty dwarf galaxies and no correlation is visible between the axis ratios (b/a) and the dust attenuation. These findings indicate that it is unlikely that the large dust attenuation is due to projection effects, but a prolate or disc- on oblate geometry is still possible, at least for a sub-sample of the sources. We have found that the distribution of HELM sources is slightly skewed towards more clustered environments than non-dusty dwarfs and tends to be slightly less star- forming. This finding, if confirmed by spectroscopic follow-up, indicates that HELM sources could be going through some environmental processes, such as galaxy interactions.

@article{2026A&A...706A.363B, author = {{Bisigello}, L. and {Gandolfi}, G. and {Grazian}, A. and {Rodighiero}, G. and {Girardi}, G. and {Renzini}, A. and {Vietri}, A. and {McGrath}, E. and {Holwerda}, B. and {Abdurro'uf}, A. and {Castellano}, M. and {Giulietti}, M. and {Gruppioni}, C. and {Hathi}, N. and {Koekemoer}, A. M. and {Lucas}, R. and {Pacucci}, F. and {P{\'e}rez-Gonz{\'a}lez}, P. G. and {Yung}, L. Y. A. and {Arrabal Haro}, P. and {Backhaus}, B. E. and {Bagley}, M. and {Dickinson}, M. and {Finkelstein}, S. and {Kartaltepe}, J. and {Kirkpatrick}, A. and {Papovich}, C. and {Pirzkal}, N.}, title = {{HELM's deep: Highly extincted low-mass galaxies seen by JWST}}, journal = {\aap}, keywords = {galaxies: dwarf, galaxies: peculiar}, year = {2026}, month = feb, volume = {706}, eid = {A363}, pages = {A363}, doi = {10.1051/0004-6361/202556903}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...706A.363B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, morphology, obscuration, sample selection, sed}, eprint = {2512.14822}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots

Seok-Jun Chang, Max Gronke, Jorryt Matthee, and 1 more author

Monthly Notices of the Royal Astronomical Society, Feb 2026

Abs DOI ADS arXiv

Little Red Dots (LRDs) are compact sources at discovered through James Webb Space Telescope spectroscopy. Their spectra exhibit broad Balmer emission lines (), alongside absorption features and a pronounced Balmer break ─ evidence for a dense, neutral hydrogen medium, in which the state is significantly populated. When interpreted as arising from active galactic nucleus broad-line regions, inferred black hole masses from local scaling relations exceed expectations given their stellar masses, challenging models of early black hole─galaxy co-evolution. However, radiative transfer effects in dense media may also impact the formation of hydrogen emission lines. We model three scattering processes shaping hydrogen line profiles: resonance scattering by hydrogen in the state, Raman scattering of ultraviolet (UV) radiation by ground-state hydrogen, and Thomson scattering by free electrons. Using 3D Monte Carlo radiative transfer simulations, we examine their imprint on line shapes and ratios. Resonance scattering produces strong deviations from Case B flux ratios, clear differences between H and H, and encodes gas kinematics in line profiles but cannot broaden H due to conversion to Pa. While Raman scattering can yield broad wings, scattering of the UV continuum is disfavoured given the absence of strong full width at half-maximum variations across transitions. Raman scattering of higher Lyman-series emission can produce H/H wing width ratios of , agreeing with observations. Thomson scattering can reproduce the observed wings under plausible conditions ─ e.g. K and ─ and lead to black hole mass overestimates by factors . Our results provide a framework for interpreting hydrogen lines in LRDs and similar systems.

@article{2026MNRAS.545f2131C, author = {{Chang}, Seok-Jun and {Gronke}, Max and {Matthee}, Jorryt and {Mason}, Charlotte}, title = {{Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots}}, journal = {\mnras}, keywords = {line: formation, radiative transfer, scattering, galaxies: active, galaxies: high-redshift, quasars: emission lines, Astrophysics of Galaxies}, year = {2026}, month = feb, volume = {545}, number = {4}, eid = {staf2131}, pages = {staf2131}, doi = {10.1093/mnras/staf2131}, archiveprefix = {arXiv}, eprint = {2508.08768}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.545f2131C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, simulation, theory}, month_numeric = {2} }

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Extreme Emission Line Galaxies in CEERS Are Powered by Star Formation, not AGN

Kelcey Davis, Madisyn Brooks, Jonathan R. Trump, and 28 more authors

arXiv e-prints, Feb 2026

Abs ADS arXiv

We present a spectroscopic study of photometrically identified extreme emission-line galaxies (EELGs) with observed-frame equivalent widths (EWs) >5000 A of either H alpha or H beta + [OIII] in the CEERS legacy deep field utilizing JWST NIRSpec spectroscopy from the CAPERS, RUBIES, THRILS and CEERS surveys. This master sample allows for performance tests of photometric selections and unveils what types of sources, either AGN or young star formation, were producing excessive ionizing radiation in the early Universe. We identify AGN through broad H alpha emission- lines and report 6 new broad-line AGN at 3.5<z<7 identified by the deep (\raisebox-0.5ex\textasciitilde8 hr) G395M THRILS survey. We investigate the photometrically selected EELGs in a color-color plot designed for “Little Red Dot” selection and demonstrate that it effectively removes AGN with non-extreme lines from the sample. EELGs with and without broad lines show similar optical line ratios. We compare emission-line morphology to EWs and continuum morphologies and find that [OIII] morphology is more compact at higher EW. \raisebox-0.5ex\textasciitilde10% of photometrically selected EELGs have broad Balmer lines, jumping to 35% in deep spectroscopy which indicates a significant fraction of photometrically selected EELGs may host AGN. However, many AGN selected as EELGs have incorrectly high photometric EWs. For sources with extreme emission-line EWs that pass our photometric criteria and host an AGN, we find that the narrow H alpha component dominates over the broad, especially in the highest-EW sources. This implies that even when an AGN is present, it does not dominate the extreme emission.

@article{2026arXiv260223310D, author = {{Davis}, Kelcey and {Brooks}, Madisyn and {Trump}, Jonathan R. and {Fern{\'a}ndez}, Vital and {Hutchison}, Taylor A. and {Larson}, Rebecca L. and {Taylor}, Anthony J. and {McGrath}, Elizabeth J. and {Barro}, Guillermo and {Koekemoer}, Anton M. and {Arrabal Haro}, Pablo and {Dickinson}, Mark and {Backhaus}, Bren E. and {Cleri}, Nikko J. and {Finkelstein}, Steven L. and {Ganapathy}, Ananya and {Simons}, Raymond C. and {Amor{\'\i}n}, Ricardo O. and {de la Vega}, Alexander and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Hu}, Weida and {Johnson}, Jarrett L. and {Kartaltepe}, Jeyhan S. and {Kocevski}, Dale and {Llerena}, Mario and {Lucas}, Ray A. and {Marshall}, Madeline A. and {Pacucci}, Fabio and {Pentericci}, Laura and {Upton Sanderbeck}, Phoebe R.}, title = {{Extreme Emission Line Galaxies in CEERS Are Powered by Star Formation, not AGN}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = feb, eid = {arXiv:2602.23310}, pages = {arXiv:2602.23310}, archiveprefix = {arXiv}, eprint = {2602.23310}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260223310D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, non-agn, spectroscopy, starburst}, month_numeric = {2} }

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Direct pathway to the Early Supermassive Black Holes: A Red Super-Eddington Quasar in a Massive Starburst Host at z=7.2

Qinyue Fei, Seiji Fujimoto, Gabriel Brammer, and 24 more authors

arXiv e-prints, Feb 2026

Abs ADS arXiv

We present a panchromatic optical-mm characterization of GNz7q, a recently identified X-ray weak, rapidly growing red quasar embedded within a dusty starburst galaxy at z=7.1899, using the full suite of JWST/NIRCam, NIRSpec, MIRI, and archival NOEMA observations. Our deep NIRSpec/G395M spectroscopy reveals unambiguous broad Balmer emission (FWHM =2221\pm20kms^-1), confirming a super-Eddington accreting black hole (λ_\rm Edd=2.7\pm0.4) with a mass of \log(M_\rm BH/M_⊙)=7.55\pm0.34, using accretion-rate corrected BH mass estimators. After subtracting the point source, we robustly detect stellar emission from the host galaxy across multiple NIRCam and MIRI filters. Out joint morphological-spectral analysis yields a stellar mass of \log (M_*/M_⊙)=10.5\pm0.4 and an intense star formation rate of \rm SFR=330\pm97 M_⊙\,\rm yr^-1, confirming the host as a massive, dusty starburst galaxy. We find that GNz7q lies on the local M_\rm BH-M_* relation (M_\rm BH/M_*≃0.001) and is well positioned to evolve into the locus of massive SDSS quasars with \log (M_\rm BH/M_⊙)≈9 and M_*≈10^11 M_⊙at z∼6, owing to its remarkably rapid growth in both the black hole and its host galaxy. This stands in stark contrast to many recently reported JWST AGN populations at similar redshifts, including the little red dots (LRDs), whose weak or undetected star formation makes it difficult for them to grow into the massive galaxies hosting SDSS-like quasars. These results suggest that GNz7q marks as a rare, pivotal phase of early BH-galaxy co-eolution, plausibly providing a crucial direct pathway to the supermassive black hole systems within the first billion years of the Universe.

@article{2026arXiv260212325F, author = {{Fei}, Qinyue and {Fujimoto}, Seiji and {Brammer}, Gabriel and {Li}, Ruancun and {Ho}, Luis C. and {Bromm}, Volker and {{\'A}lvarez-M{\'a}rquez}, Javier and {Asada}, Yoshihisa and {Barro}, Guillermo and {Colina}, Luis and {Dayal}, Pratika and {Finkelstein}, Steven L. and {Fynbo}, Johan P. U. and {Ginolfi}, Michele and {Inayoshi}, Kohei and {Kokorev}, Vasily and {Leung}, Gene C. K. and {Matthee}, Jorryt and {Meyer}, Romain A. and {Naidu}, Rohan P. and {Onoue}, Masafusa and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Steinhardt}, Charles L. and {Valentino}, Francesco and {Walter}, Fabian and {Xiao}, Mengyuan and {Zhang}, Haowen}, title = {{Direct pathway to the Early Supermassive Black Holes: A Red Super-Eddington Quasar in a Massive Starburst Host at $z=7.2$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = feb, eid = {arXiv:2602.12325}, pages = {arXiv:2602.12325}, archiveprefix = {arXiv}, eprint = {2602.12325}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260212325F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {host galaxy, jwst, spectroscopy, starburst, super-eddington}, month_numeric = {2} }

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Back to Normal Again: Possible Destinies of JWST overmassive SMBHs and “Little Red Dots” in the View of Shin-Uchuu Simulation

Haojie Hu, Hiroto Yanagisawa, Moka Nishigaki, and 3 more authors

arXiv e-prints, Feb 2026

Abs ADS arXiv

The James Webb Space Telescope (JWST) has enabled the discovery of hundreds of supermassive black holes (SMBHs) at redshifts zrsim 4-7. A non-negligible fraction of these SMBHs are hosted in galaxies with BH-to-galaxy mass ratios (M_\rm BH/M_⋆) being excessively larger than that for local SMBHs by ∼1-2 dex. The origin of these “overmassive“ BHs remains elusive, demanding either a heavy seed formation scenario or rapid growth of seed BHs. Their deviation from local scaling relations challenges our understanding of how SMBHs and their host galaxies coevolve across cosmic time. In this paper, we apply phenomenological modelings for BHs and galaxies to dark matter halo merger histories from N-body simulations to investigate the subsequent evolution of JWST-discovered “overmassive” SMBHs. We find that early evolution of “overmassive” SMBHs is dominated by stunted accretion leading to gradual decreases in M_\rm BH/M_⋆ratios. In contrast, less massive SMBHs experience super-Eddington accretion during their early evolution, resulting in a slow increase of mass ratios toward M_\rm BH/M_⋆∼0.01. Convergence occurs at M_\rm BH∼10^8~M_⊙with M_\rm BH/M_⋆∼0.01. At lower redshift, nearly all SMBHs evolve onto local relations, as expected given that our models adopt empirical relations derived from low-redshift observations. This suggests that the global feedback mechanisms regulating the coevolution of M_\rm BH/M_⋆ratios are implicitly encoded in local relations in terms of star-formation rate distribution, black hole accretion rate distribution and their active (quiescent) fractions.

@article{2026arXiv260214496H, author = {{Hu}, Haojie and {Yanagisawa}, Hiroto and {Nishigaki}, Moka and {Kiyota}, Tomokazu and {Ishiyama}, Tomoaki and {Ohsuga}, Ken}, title = {{Back to Normal Again: Possible Destinies of JWST overmassive SMBHs and ``Little Red Dots'' in the View of Shin-Uchuu Simulation}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = feb, eid = {arXiv:2602.14496}, pages = {arXiv:2602.14496}, archiveprefix = {arXiv}, eprint = {2602.14496}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260214496H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {heavy seed, jwst, simulation, super-eddington, theory}, month_numeric = {2} }

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RUBIES: A spectroscopic census of little red dots: All point sources with v-shaped continua have broad lines (Corrigendum)

Raphael E. Hviding, Anna de Graaff, Tim B. Miller, and 16 more authors

Astronomy & Astrophysics, Feb 2026

DOI ADS

@article{2026A&A...706C...3H, author = {{Hviding}, Raphael E. and {de Graaff}, Anna and {Miller}, Tim B. and {Setton}, David J. and {Greene}, Jenny E. and {Labb{\'e}}, Ivo and {Brammer}, Gabriel and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Cleri}, Nikko J. and {Leja}, Joel and {Maseda}, Michael V. and {McConachie}, Ian and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Oesch}, Pascal A. and {Wang}, Bingjie and {Whitaker}, Katherine E. and {Williams}, Christina C.}, title = {{RUBIES: A spectroscopic census of little red dots: All point sources with v-shaped continua have broad lines (Corrigendum)}}, journal = {\aap}, keywords = {errata, addenda, galaxies: active, galaxies: high-redshift}, year = {2026}, month = feb, volume = {706}, eid = {C3}, pages = {C3}, doi = {10.1051/0004-6361/202659153e}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...706C...3H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {catalog, emission lines, spectroscopy}, month_numeric = {2} }

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Little Red Dots and Their Progenitors from Direct Collapse Black Holes

Junehyoung Jeon, Boyuan Liu, Volker Bromm, and 7 more authors

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has discovered a new population of objects, the Little Red Dots (LRDs), characterized by V-shaped spectra indicative of strong breaks around the Balmer limit and a compact morphology that gave them their name. A popular explanation is that they are a subpopulation of active galactic nuclei (AGN) and/or supermassive black holes (SMBHs) predominantly found in the high-redshift Universe (z \ensuremath≳ 3). Similarly, direct collapse black holes (DCBHs), theorized to form from collapsing massive, extremely metal-poor gas clouds, have been invoked to explain high-redshift quasars, the most massive AGN subpopulation. Here, we employ the semianalytical code A-SLOTH to produce a population of DCBHs and compare them against observed LRD demographics and properties. Specifically, we compare the DCBH- seeded SMBH population against the standard stellar-remnant seeds and find that the DCBH models agree better with the observed LRD population statistics and host halo properties. Furthermore, for the most extreme and earliest LRD detections, interpreted to be systems with an AGN but small stellar component, DCBHs are able to reproduce the observed spectral shape and properties under multiple scenarios—high dust attenuation or AGN surrounded by dense gas—that have been proposed to explain the unique shape of LRD spectra. Even when super-Eddington accretion, invoked previously to explain the nature of LRDs, is enforced on stellar-remnant seeds, the spectral characteristics of extreme LRDs cannot be reproduced. We emphasize the importance of gas-metallicity observations as an additional dimension besides the widely used SMBH to stellar mass ratios to further constrain the progenitors of LRDs.

@article{2026ApJ...998..148J, author = {{Jeon}, Junehyoung and {Liu}, Boyuan and {Bromm}, Volker and {Fujimoto}, Seiji and {Taylor}, Anthony J. and {Kokorev}, Vasily and {Larson}, Rebecca L. and {Chisholm}, John and {Finkelstein}, Steven L. and {Kocevski}, Dale D.}, title = {{Little Red Dots and Their Progenitors from Direct Collapse Black Holes}}, journal = {\apj}, keywords = {Early universe, Galaxy formation, Supermassive black holes, Active galactic nuclei, Theoretical models, 435, 595, 1663, 16, 2107}, year = {2026}, month = feb, volume = {998}, number = {1}, eid = {148}, pages = {148}, doi = {10.3847/1538-4357/ae3725}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...998..148J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, heavy seed, jwst, sed, theory}, eprint = {2508.14155}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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MIDIS: The identification of deep MIRI-red sources as candidates for extreme Balmer-break and line emitting galaxies at high-z

I. Jermann, G. Brammer, S. Gillman, and 27 more authors

arXiv e-prints, Feb 2026

Abs ADS arXiv

We investigate the detection and nature of 5.6\raisebox-0.5ex~\ensuremathμm MIRI-red sources in the MIRI Deep Imaging Survey (MIDIS), covering 2.4\raisebox-0.5ex\textasciitildearcmin^2 in the Hubble Ultra Deep Field. MIDIS is the deepest JWST/MIRI survey to date, probing faint limits and enabling studies of rare high-redshift galaxy populations. We define MIRI-red sources as those detected at 5σ significance in MIRI/F560W with red colors: m_\rm F444W - m_\rm F560W \ge 0.5. Using an empirical methodology, we estimate the purity and completeness of MIRI detections and find that a 5-sigma detection at 28.75 mag has a purity of 92\% and completeness of 54\%. We identify seven MIRI-red galaxy candidates, including an F115W dropout consistent with a high-redshift galaxy candidate. We explore possible physical origins for the MIRI-red population, including active galactic nuclei, dust-obscured galaxies, extreme emission-line galaxies, evolved stellar populations, and Little Red Dots (LRDs). Given the proximity of the F444W and F560W filters and the depth of MIDIS, MIRI-red galaxies are consistent with emission-line galaxies with EW_0(Hα) \ge 750 Å or EW_0(Hβ+ [OIII]) \ge 600 Å, or high-redshift Balmer breaks of at least 1.6. We also discuss an extreme MIRI- red galaxy undetected in F444W, a potential MIRI-only source, for which we derive EW_0(Hα) ∼6000 Å and EW_0(Hβ+ [OIII]) ∼4000 Å, or high-z LRD analogs with Balmer breaks of 6.3. Finally, we find fewer MIRI-red detections than expected from extrapolations of the Hα or Hβ+[OIII] line luminosity functions, consistent with previous deep searches, while the absence of z>10 LRD candidates agrees with theoretical expectations for the MIDIS volume.

@article{2026arXiv260217329J, author = {{Jermann}, I. and {Brammer}, G. and {Gillman}, S. and {Greve}, T. R. and {Boogaard}, L. A. and {Melinder}, J. and {Meyer}, R. A. and {P{\'e}rez-Gonz{\'a}lez}, P. G. and {Rinaldi}, P. and {Colina}, J. L. and {{\"O}stlin}, G. and {Wright}, G. and {{\'A}lvarez-M{\'a}rquez}, J. and {Bik}, A. and {Caputi}, K. I. and {Crespo G{\'o}mez}, A. and {Costantin}, L. and {Hjorth}, J. and {Iani}, E. and {Kendrew}, S. and {Labiano}, A. and {Langeroodi}, D. and {Peissker}, F. and {Prieto-Jim{\'e}nez}, C. and {Pye}, J. P. and {Tikkanen}, T. V. and {Walter}, F. and {van der Werf}, P. and {Henning}, T. and {Shuntov}, M.}, title = {{MIDIS: The identification of deep MIRI-red sources as candidates for extreme Balmer-break and line emitting galaxies at high-z}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = feb, eid = {arXiv:2602.17329}, pages = {arXiv:2602.17329}, archiveprefix = {arXiv}, eprint = {2602.17329}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260217329J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, photometry, sed}, month_numeric = {2} }

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The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes

Xiaojing Lin, Xiaohui Fan, Zheng Cai, and 25 more authors

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

JWST observations have revealed a population of high-redshift “little red dots” (LRDs) that challenge conventional active galactic nucleus (AGN) models. We report the discovery of three local LRDs at z = 0.1─0.2, initially selected from the Sloan Digital Sky Survey database, with follow-up optical/near-IR spectroscopy and photometry. They exhibit properties fully consistent with those of high-redshift LRDs, including broad hydrogen and helium emission lines, compact morphologies, V-shaped UV-optical spectral energy distribution, declining near-IR continua, and no significant variability. Two sources were targeted but not detected in X-rays with statistical significance. All three sources show blue-shifted He I absorption, while two exhibit H\ensuremathα and Na D absorption lines. We detect full Balmer and Paschen line series in all three objects, along with abundant narrow [Fe II] emission in two. The emission-line analyses suggest narrow lines originate from AGN-powered, metal- poor regions with minimal dust; broad lines come from inner regions with exceptionally high density or atypical dust properties; and [Fe II] emission arises from dense gas between broad- and narrow-line regions. One of our objects, J1025+1402 (nicknamed “The Egg”), shows extremely high equivalent width Na D, K I, and Ca II triplet absorption lines, along with other potential low-ionization absorption features, suggesting the presence of a cool (\ensuremath∼5000 K), metal-enriched gas envelope. The optical/near-IR continua of these LRDs are also consistent with theoretical models featuring an atmosphere around black holes (BHs). The Wide-field Infrared Survey Explorer─detected IR emission is consistent with weak dust emission of T \ensuremath∼ 10^2─10^3 K. We propose a conceptual model consisting of a largely thermalized cool-gas envelope surrounding the central BH and an extended emission-line region with high-density outflowing gas to explain the observed properties of these local LRDs.

@article{2026ApJ...997..364L, author = {{Lin}, Xiaojing and {Fan}, Xiaohui and {Cai}, Zheng and {Bian}, Fuyan and {Liu}, Hanpu and {Sun}, Fengwu and {Ma}, Yilun and {Greene}, Jenny E. and {Strauss}, Michael A. and {Green}, Richard and {Lyu}, Jianwei and {Champagne}, Jaclyn B. and {Goulding}, Andy D. and {Inayoshi}, Kohei and {Jin}, Xiangyu and {Leung}, Gene C. K. and {Li}, Mingyu and {Liu}, Weizhe and {Liu}, Yichen and {Mao}, Junjie and {Pudoka}, Maria Anne and {Tee}, Wei Leong and {Wang}, Ben and {Wang}, Feige and {Wu}, Yunjing and {Yang}, Jinyi and {Zhang}, Haowen and {Zhu}, Yongda}, title = {{The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes}}, journal = {\apj}, keywords = {Black holes, Active galactic nuclei, High-redshift galaxies, 162, 16, 734, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, Solar and Stellar Astrophysics}, year = {2026}, month = feb, volume = {997}, number = {2}, eid = {364}, pages = {364}, doi = {10.3847/1538-4357/ae2bdf}, archiveprefix = {arXiv}, eprint = {2507.10659}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...997..364L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, local counterpart, sed, spectroscopy}, month_numeric = {2} }

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Improved measurements of the age of JWST galaxies at z = 6 \ensuremath- 10

M. López-Corredoira and C. M. Gutiérrez

Monthly Notices of the Royal Astronomical Society, Feb 2026

Abs DOI ADS arXiv

From James Webb Space Telescope (JWST) surveys, 31 galaxies with average redshift 7.3 are selected containing large Balmer break, Lyman- break (V-shaped SED versus ). Apart from Hubble Space Telescope (HST) and JWST-NIRCam (Near-infrared camera) photometry for these galaxies, there are JWST-NIRSpec spectra for 13 galaxies and mid-infrared photometry (mostly JWST-MIRI) for 15 of them. Spectroscopical analyses included Balmer emission lines, Balmer + 4000 Å breaks or Ca II lines. Spectral energy distribution (SED) fitting with photometry include old and young stellar populations, emission lines associated to H II regions, active galactic nucleus (AGN), interstellar dust extinction, and intergalactic extinction from neutral hydrogen. By adopting realistic extinction curves and taking into account the V-shaped SED and low emission at near-infrared at rest, the analyses show that AGN contribution in these galaxies (’little red dots’ most of them) should be small on average in the reddest wavelengths, though important for few of the 31 galaxies. Average age of the 31 galaxies: (95 per cent CL) Gyr, while the average age of the Lambda cold dark matter (CDM) universe is 0.70 Gyr. This corresponds to a formation epoch (97.5 per cent CL). Reddest galaxies present largest ages. One of these very red galaxies gets an age incompatible to be younger than the age of the Universe within . TP-AGB effect cannot explain this tension. None the less, there may be other uncertainties in the models, so this tension is a provisional result and further research is needed to confirm it.

@article{2026MNRAS.546ag089L, author = {{L{\'o}pez-Corredoira}, M. and {Guti{\'e}rrez}, C. M.}, title = {{Improved measurements of the age of JWST galaxies at z = 6 {\ensuremath{-}} 10}}, journal = {\mnras}, keywords = {galaxies: high-redshift, cosmology: observations, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2026}, month = feb, volume = {546}, number = {2}, eid = {stag089}, pages = {stag089}, doi = {10.1093/mnras/stag089}, archiveprefix = {arXiv}, eprint = {2601.16772}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.546ag089L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, photometry, sed, spectroscopy}, month_numeric = {2} }

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Little Red Dots as Obscured Little Blue Dots: A Super-Eddington Unification Model

Piero Madau and Roberto Maiolino

arXiv e-prints, Feb 2026

Abs ADS arXiv

We test whether “Little Red Dots” (LRDs) are dust-reddened, high- inclination counterparts of compact, blue broad-line AGNs (“Little Blue Dots”, LBDs) powered by super-Eddington accretion. We model the central engine as a geometrically thick, radiation-pressure supported accretion flow whose funnel yields strongly anisotropic, intrinsically blue ionizing continua, coupled to an equatorially concentrated BLR and a dusty screen with modest covering factor. Using inclination-dependent SEDs as input to Cloudy, we show that the extreme broad Halpha equivalent widths (EWs) of JWST LRDs are reproduced with global BLR covering factors of only 15%, consistent with standard Type 1 AGNs. Large Balmer EWs arise because self-shadowing suppresses the high-inclination optical continuum while the BLR is illuminated by an EUV-rich SED. Weak high-ionization lines follow from orientation-dependent suppression of the XUV/soft X-ray continuum toward equatorial directions, without requiring a fully enclosing gaseous “cocoon”. With a gray attenuation law of AV = 2.8 along LRD-selected sightlines, the fiducial model matches the V-shaped UV-optical continua and large Balmer decrements; strong Balmer breaks occur only for the most obscured views. A compact equatorial dust component tied to the BLR and normalized by energy conservation intercepts and reradiates only a small fraction of Lbol, producing a modest hot-dust bump and far-IR/sub-mm emission consistent with current limits and implying small dust masses. The model unifies LRD and LBD observables via orientation, predicting correlated trends in Halpha EW, Balmer decrement, Balmer break, high-ionization line strengths, and IR emission.

@article{2026arXiv260222386M, author = {{Madau}, Piero and {Maiolino}, Roberto}, title = {{Little Red Dots as Obscured Little Blue Dots: A Super-Eddington Unification Model}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = feb, eid = {arXiv:2602.22386}, pages = {arXiv:2602.22386}, archiveprefix = {arXiv}, eprint = {2602.22386}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260222386M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, dust-reddened, jwst, sed, super-eddington}, month_numeric = {2} }

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Black holes disguised as little red dots

Jorryt Matthee

Science, Feb 2026

Abs DOI ADS

There may be a newly identified early phase of supermassive black hole growth

@article{2026Sci...391..767M, author = {{Matthee}, Jorryt}, title = {{Black holes disguised as little red dots}}, journal = {Science}, year = {2026}, month = feb, volume = {391}, number = {6787}, pages = {767-768}, doi = {10.1126/science.adz8603}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026Sci...391..767M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, heavy seed, super-eddington, theory}, month_numeric = {2} }

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Supermassive Stars Match the Spectral Signatures of JWST’s Little Red Dots

Devesh Nandal and Abraham Loeb

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has unveiled a population of enigmatic, compact sources at high redshift known as “little red dots” (LRDs), whose physical nature remains a subject of intense debate. Concurrently, the rapid assembly of the first supermassive black holes (SMBHs) requires the formation of heavy seeds, for which supermassive stars (SMSs) are leading theoretical progenitors. In this work, we perform the first quantitative test of the hypothesis that LRDs are the direct observational manifestation of these primordial SMSs. We present a novel, first-principles pipeline generating synthetic spectra for a nonrotating, metal-free SMS up to 10^6 M_\ensuremath⊙. We establish that its luminosity (L_\ensuremathλ ≍ 1.7 \texttimes 10^44 erg s^\ensuremath-1 \ensuremathμm^\ensuremath-1 at 4050 Å) provides a decisive constraint, matching prominent LRDs. Our model self-consistently reproduces their defining spectral features: the V-shaped Balmer break morphology is shown to be an intrinsic photospheric effect, while the complex line phenomenology, strong H\ensuremathβ in emission with other Balmer lines in absorption arises from non-LTE effects in a single stellar atmosphere. With wind and macroturbulent broadening, we match LRD spectra at z = 7.76 and z = 3.55, including the H\ensuremathβ width of MoM-BH*-1 to within 4%. We predict a luminosity-dependent observability window, \ensuremath∼10^4 yr for the most luminous systems and 10^5─10^6 yr if L_\ensuremathλ(4050 Å) is lower by 1─2 dex. These results provide a self-consistent alternative to multicomponent obscured active galactic nucleus scenarios and suggest JWST may be witnessing luminous stages of SMBH progenitors before collapse.

@article{2026ApJ...998..124N, author = {{Nandal}, Devesh and {Loeb}, Abraham}, title = {{Supermassive Stars Match the Spectral Signatures of JWST's Little Red Dots}}, journal = {\apj}, keywords = {Massive stars, Stellar evolutionary models, Supermassive black holes, Early universe, Stellar accretion, Stellar properties, 732, 2046, 1663, 435, 1578, 1624, Astrophysics of Galaxies, Solar and Stellar Astrophysics}, year = {2026}, month = feb, volume = {998}, number = {1}, eid = {124}, pages = {124}, doi = {10.3847/1538-4357/ae32f3}, archiveprefix = {arXiv}, eprint = {2507.12618}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...998..124N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {exotic physics, heavy seed, jwst, sed, spectroscopy}, month_numeric = {2} }

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Discovery of an X-Ray Luminous Radio-loud Quasar at z = 3.4: A Possible Transitional Super-Eddington Phase

Sakiko Obuchi, Kohei Ichikawa, Satoshi Yamada, and 11 more authors

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

We report the multiwavelength properties of eROSITA Final Equatorial Depth Survey (eFEDS) J084222.9+001000 (hereafter ID830), a quasar at z = 3.4351, identified as the most X-ray luminous radio-loud quasar in the eFEDS field. ID830 shows a rest-frame 0.5─2 keV luminosity of log(L0.5\ensuremath-2keV/ergs\ensur emath-1)=46.20\ensuremath\pm0.12, with a steep X-ray photon index (\ensuremathΓ = 2.43 \ensuremath\pm 0.21), and a significant radio counterpart detected with the Very Large Array FIRST 1.4 GHz and Very Large Array Sky Survey 3 GHz bands. The rest-frame UV to optical spectra from Sloan Digital Sky Survey and Subaru/MOIRCS J band show a dust-reddened quasar feature with A_V = 0.39 \ensuremath\pm 0.08 mag, and the expected bolometric active galactic nuclei luminosity from the dust-extinction-corrected UV luminosity reaches L_bol,3000Å = (7.62 \ensuremath\pm 0.31) \texttimes 10^46 erg s^\ensuremath-1. We estimate a black hole mass of M_BH = (4.40 \ensuremath\pm 0.72) \texttimes 10^8 M_\ensuremath⊙ based on the Mg II\ensuremathλ2800 emission-line width, and Eddington ratios from the dust-extinction-corrected UV continuum luminosity and X-ray luminosity that reach \ensuremathλ_Edd,UV = 1.44 \ensuremath\pm 0.24 and \ensuremathλ_Edd,X = 12.8 \ensuremath\pm 3.9, respectively, both indicating super-Eddington accretion. ID830 shows a high ratio of UV to X-ray luminosities, \ensuremathα_OX = \ensuremath-1.20 \ensuremath\pm 0.07 (or \ensuremathα_OX = \ensuremath-1.42 \ensuremath\pm 0.07 after correcting for jet-linked X-ray excess), higher than quasars and little red dots in the super-Eddington phase with similar UV luminosities, with \ensuremathα_OX < \ensuremath-1.8. Such a high \ensuremathα_OX suggests the coexistence of a prominent radio jet and X-ray corona in this high-Eddington- accretion phase. We propose that ID830 may be in a transitional phase after an accretion burst, evolving from a super-Eddington to a sub-Eddington state, which could naturally describe the high \ensuremathα_OX.

@article{2026ApJ...997..156O, author = {{Obuchi}, Sakiko and {Ichikawa}, Kohei and {Yamada}, Satoshi and {Kawakatu}, Nozomu and {Liu}, Teng and {Matsumoto}, Naoki and {Merloni}, Andrea and {Takahashi}, Kosuke and {Zaw}, Ingyin and {Chen}, Xiaoyang and {Hada}, Kazuhiro and {Igo}, Zsofi and {Suh}, Hyewon and {Wolf}, Julien}, title = {{Discovery of an X-Ray Luminous Radio-loud Quasar at z = 3.4: A Possible Transitional Super-Eddington Phase}}, journal = {\apj}, keywords = {Supermassive black holes, Active galactic nuclei, Radio jets, 1663, 16, 1347}, year = {2026}, month = feb, volume = {997}, number = {2}, eid = {156}, pages = {156}, doi = {10.3847/1538-4357/ae1d6d}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...997..156O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, multi-wavelength, radio, x-ray}, eprint = {2511.05029}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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Tracking the Assembly of Supermassive Black Holes: A Comparison of Diverse Models across Cosmic Time

Antonio J. Porras-Valverde, Angelo Ricarte, Priyamvada Natarajan, and 3 more authors

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

Galaxies grow alongside central supermassive black holes (SMBHs) through fueling and feedback. However, the origins of this coevolution remain unclear and vary across modeling frameworks. Using semianalytic models (SAMs), we trace SMBH mass assembly across M_BH \ensuremath∼ 10^6\ensuremath-10 M_\ensuremath⊙. We find significant discrepancies between observations and physics-based models of the local black hole mass function (BHMF), likely from differences in the stellar mass function and scaling relations used to infer the BHMF. Most physics-based models agree at z \ensuremath∼ 1─4 and broadly match the JWST broad-line active galactic nucleus (AGN) BHMFs at z = 4─5. These models also reproduce the observed bolometric AGN luminosity evolution, except the SAM DARK SAGE, which predicts an excess. Interestingly, this pronounced “knee” in the bolometric AGN luminosity function predicted by DARK SAGE around L_bol \ensuremath∼ 10^46 erg s^\ensuremath-1 is consistent with the inferred abundance and luminosity of “little red dots” at z = 5─6, under the assumption that they are powered entirely by AGN activity. In contrast to other models, DARK SAGE deploys multiple growth channels for SMBHs that include mergers, hot- mode accretion, merger-driven cold-accretion, and secular- instability-driven accretion. We analyze the black hole mass buildup and accretion histories in DARK SAGE, which, unlike other models, also allows for super-Eddington accretion, and we find that, on average, SMBHs primarily grow through secular disk instabilities and merger-driven cold gas accretion modes. We also find that black hole mergers contribute the majority of the growth of \ensuremath∼60% of the total mass budget only for the most massive SMBHs by z = 0.

@article{2026ApJ...998...48P, author = {{Porras-Valverde}, Antonio J. and {Ricarte}, Angelo and {Natarajan}, Priyamvada and {Somerville}, Rachel S. and {Gabrielpillai}, Austen and {Yung}, L. Y. Aaron}, title = {{Tracking the Assembly of Supermassive Black Holes: A Comparison of Diverse Models across Cosmic Time}}, journal = {\apj}, keywords = {Astrophysical black holes, Galaxy formation, 98, 595, Astrophysics of Galaxies}, year = {2026}, month = feb, volume = {998}, number = {1}, eid = {48}, pages = {48}, doi = {10.3847/1538-4357/ae2fb1}, archiveprefix = {arXiv}, eprint = {2504.11566}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...998...48P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, simulation, super-eddington, theory}, month_numeric = {2} }

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Little Red Dots: One Photometric Tag Concealing Diverse Spectroscopic Flavors of Massive Star Formation and Black Hole Activity

Pablo G. Pérez-González, Guillermo Barro, Stefano Carniani, and 62 more authors

arXiv e-prints, Feb 2026

Abs ADS arXiv

We compile JWST/NIRSpec prism and MIRI data for 249 Little Red Dots (LRDs) at 2.3<z<9.3, forming a representative spectroscopic subset of NIRCam-selected LRDs. We derive a median stacked spectrum covering rest-frame 0.09-1.2 μm, with MIRI photometry extending the spectral energy distribution to 4 μm. Four additional stacks for subsamples defined by optical-to-UV luminosity ratios show that LRDs form a heterogeneous population spanning diverse continuum slopes and line properties. Assuming LRDs host super-massive black holes (BHs) surrounded by dense gas clouds, and stars accompany this core, we infer masses of M _BH\sim10^6.0-6.5\raisebox-0.5ex\textasciitildeM_⊙and M_\bigstar\sim10^8.3 M_⊙, corresponding to BH-to- stellar mass ratios of 1-2%. The stacks show ubiquitous UV and optical FeII emission, indicating a direct view of the broad- line region and high (but sub-Eddington) accretion (λ_Edd=0.6\pm0.2). We find a significant stellar contribution in the far-UV, reaching \sim80% in the bluest systems. Possible Wolf-Rayet features (HeIIλ4687, nitrogen lines) are identified, tracing a young (3-7 Myr) compact starburst event. We also detect strong Balmer breaks and atypical Balmer, Paschen, [OIII], and optical and near-infrared HeI line ratios, and an absorption at \sim4550 Angstrom (probably linked to FeII), all consistent with radiative- transfer effects in high-density gas with warm temperatures (4000-7000 K). We find a diversity of LRD flavors modulated by the luminosity ratio between between a short (\lesssim20 Myr) and intense phase of BH activity, the most extreme stage lasting \sim3-7 Myr, characterized by near-Eddington-limit radiation, and a nuclear and compact starburst dominated by massive stars (even super-massive, \mathrmM_\mathrmSMS\sim10^5 M_⊙), all embedded in dense gas with modest dust content producing a variety of optical depths.

@article{2026arXiv260220247P, author = {{P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Barro}, Guillermo and {Carniani}, Stefano and {D'Eugenio}, Francesco and {Rieke}, George H. and {Tripodi}, Roberta and {Bunker}, Andrew J. and {Ji}, Xihan and {Marques-Chaves}, Rui and {Schaerer}, Daniel and {Venturi}, Giacomo and {Ar{\'e}valo-Gonz{\'a}lez}, Flor and {Arribas}, Santiago and {Rinaldi}, Pierluigi and {Rodr{\'\i}guez Del Pino}, Bruno and {Witstok}, Joris and {Bhatawdekar}, Rachana and {Boogaard}, Leindert A. and {Charlot}, Stephane and {Chevallard}, Jacopo and {Costantin}, Luca and {Curti}, Mirko and {Curtis-Lake}, Emma and {Daddi}, Emanuele and {Davis}, Kelcey and {Dickinson}, Mark and {Donnan}, Callum T. and {Donnan}, Fergus R. and {Dunlop}, James S. and {Eisenstein}, Daniel J. and {Ferguson}, Henry C. and {Fern{\'a}ndez Aranda}, Rom{\'a}n and {Finkelstein}, Steven L. and {Fujimoto}, Seiji and {Gandolfi}, Giovanni and {Giavalisco}, Mauro and {Grogin}, Norman A. and {Hamed}, Mahmoud and {Hirschmann}, Michaela and {Kartaltepe}, Jeyhan S. and {Kocevski}, Dale D. and {Koekemoer}, Anton M. and {Leung}, Gene C. K. and {Lofaro}, Cristina M. and {Lucas}, Ray A. and {McLeod}, Derek J. and {Melinder}, Jens and {{\"O}stlin}, Goran and {Papovich}, Casey and {Pentericci}, Laura and {P{\'e}rez-D{\'\i}az}, Borja and {Rieke}, Marcia and {Scholtz}, Jan and {Somerville}, Rachel S. and {Stanton}, Thomas M. and {Stevenson}, Struan D. and {Shivaei}, Irene and {Tacchella}, Sandro and {Trump}, Jonathan R. and {{\"U}bler}, Hannah and {Wang}, Xin and {Williams}, Christina C. and {Willmer}, Christopher N. A. and {Yung}, L. Y. Aaron and {Zhu}, Yongda}, title = {{Little Red Dots: One Photometric Tag Concealing Diverse Spectroscopic Flavors of Massive Star Formation and Black Hole Activity}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = feb, eid = {arXiv:2602.20247}, pages = {arXiv:2602.20247}, archiveprefix = {arXiv}, eprint = {2602.20247}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260220247P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, composite, jwst, spectroscopy, starburst}, month_numeric = {2} }

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Evolutionary Tracks and Spectral Properties of Quasi-stars and Their Correlation with Little Red Dots

Andrew D. Santarelli, Ebraheem Farag, Earl P. Bellinger, and 4 more authors

The Astrophysical Journal Letters, Feb 2026

Abs DOI ADS arXiv

JWST has revealed a population of red, compact, high-redshift (z \ensuremath∼ 3─10) objects referred to as “Little Red Dots” (LRDs). These objects exhibit unusual spectral features reminiscent of stellar spectra with blackbody-like spectral energy distributions, large hydrogen Balmer breaks, Balmer line absorption, and classical stellar absorption features such as calcium H&K and the calcium triplet. Following the recent suggestion that these may be actively accreting direct-collapse black holes in the process of assembly, i.e., quasi-stars, we present evolutionary models of quasi-stars using our recently released, publicly available MESA-QUEST modeling framework. We compute a grid of models spanning a range of black hole masses and predict the luminosities, temperatures, surface gravities, and lifetimes of these objects. We find that these models lie along a Hayashi track once they hit their “late stage,” which constitutes the majority of their lives (\ensuremath∼20 Myr). We present scaling relations for estimating the mass of a quasi-star as a function of the bolometric luminosity, as well as the bolometric luminosity as a function of the effective temperature for the Hayashi track. The short lifetimes in tandem with the observed number density of LRDs imply the possibility that every supermassive black hole detected at these epochs was once a quasi-star. We compare synthetic spectra of our quasi- star models to observations of LRDs, and show that these models are broadly capable of reproducing the continuum spectra of observed LRDs. These results indicate that quasi-stars are promising candidates for the origin of supermassive black holes via direct collapse in the early Universe.

@article{2026ApJ...998L...4S, author = {{Santarelli}, Andrew D. and {Farag}, Ebraheem and {Bellinger}, Earl P. and {Natarajan}, Priyamvada and {Naidu}, Rohan P. and {Campbell}, Claire B. and {Caplan}, Matthew E.}, title = {{Evolutionary Tracks and Spectral Properties of Quasi-stars and Their Correlation with Little Red Dots}}, journal = {\apjl}, keywords = {Black holes, Supermassive black holes, Stellar evolutionary models, Galaxies, Active galactic nuclei, 162, 1663, 2046, 573, 16, Astrophysics of Galaxies, High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics}, year = {2026}, month = feb, volume = {998}, number = {1}, eid = {L4}, pages = {L4}, doi = {10.3847/2041-8213/ae3713}, archiveprefix = {arXiv}, eprint = {2510.17952}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...998L...4S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {exotic physics, heavy seed, jwst, simulation, theory}, month_numeric = {2} }

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The warm outer layer of a little red dot as the source of [Fe II] and collisional Balmer lines with scattering wings

Alberto Torralba, Jorryt Matthee, Gabriele Pezzulli, and 22 more authors

Astronomy & Astrophysics, Feb 2026

Abs DOI ADS arXiv

The population of the little red dots (LRDs) may represent a key phase of supermassive black hole (SMBH) growth. A cocoon of dense excited gas is emerging as a key component to explain the most striking properties of LRDs, such as strong Balmer breaks and Balmer absorption, as well as the weak IR emission. To dissect the structure of LRDs, we analyzed new deep JWST/NIRSpec PRISM and G395H spectra of FRESCO-GN-9771, one of the most luminous known LRDs at z = 5.5. These spectra reveal a strong Balmer break, broad Balmer lines, and very narrow [O III] emission. We revealed a forest of optical [Fe II] lines, which we argue are emerging from a dense (n_H = 10^9 \ensuremath- 10 cm^\ensuremath-3) warm layer with electron temperature T_e ≍ 7000 K. The broad wings of H\ensuremathα and H\ensuremathβ have an exponential profile due to electron scattering in this same layer. The high H\ensuremathα : H\ensuremathβ : H\ensuremathγ flux ratio of ≍10.4 : 1 : 0.14 is an indicator of collisional excitation and resonant scattering dominating the Balmer line emission. A narrow H\ensuremathγ component, unseen in the other two Balmer lines due to outshining by the broad components, could trace the ISM of a normal host galaxy with a star formation rate of \ensuremath∼5 M_\ensuremath⊙ yr^\ensuremath-1. The warm layer is mostly opaque to Balmer transitions, producing a characteristic P Cygni profile in the line centers suggesting outflowing motions. This same layer is responsible for shaping the Balmer break. The broadband spectrum can be reasonably matched by a simple photoionized slab model that dominates the \ensuremathλ > 1500 Å continuum and a low-mass (\ensuremath∼10^8 M_\ensuremath⊙) galaxy that could explain the narrow [O III], with only a subdominant contribution to the UV continuum. Our findings indicate that Balmer lines are not directly tracing the gas kinematics near the SMBH and that the BH mass scale is likely much lower than virial indicators suggest.

@article{2026A&A...707A..75T, author = {{Torralba}, Alberto and {Matthee}, Jorryt and {Pezzulli}, Gabriele and {Naidu}, Rohan P. and {Ishikawa}, Yuzo and {Brammer}, Gabriel B. and {Chang}, Seok-Jun and {Chisholm}, John and {de Graaff}, Anna and {D'Eugenio}, Francesco and {Di Cesare}, Claudia and {Eilers}, Anna-Christina and {Greene}, Jenny E. and {Gronke}, Max and {Iani}, Edoardo and {Kokorev}, Vasily and {Kotiwale}, Gauri and {Kramarenko}, Ivan and {Ma}, Yilun and {Mascia}, Sara and {Navarrete}, Benjam{\'\i}n and {Nelson}, Erica and {Oesch}, Pascal and {Simcoe}, Robert A. and {Wuyts}, Stijn}, title = {{The warm outer layer of a little red dot as the source of [Fe II] and collisional Balmer lines with scattering wings}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift, galaxies: nuclei, quasars: supermassive black holes}, year = {2026}, month = feb, volume = {707}, eid = {A75}, pages = {A75}, doi = {10.1051/0004-6361/202557537}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...707A..75T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, obscuration, spectroscopy}, eprint = {2510.00103}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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Little red dots: the assembly of early supermassive black holes in the JWST Era

David D. Vaida and Ryan Jeffrey Farber

Frontiers in Astronomy and Space Sciences, Feb 2026

Abs DOI ADS arXiv

Since the launch of the James Webb Space Telescope (JWST) in late 2021, our understanding of high-redshift objects has faced several upheavals. JWST has discovered much more massive galaxies and supermassive black holes (SMBH) than cosmological models had expected. Furthermore, JWST observations have revealed an entirely novel population of high-redshift objects. Characterized by a dominant red rest-frame optical continuum and point-like morphology, these “little red dots” (LRD) have set off a flurry of observational and theoretical follow-up. The current identity of LRD is highly debated, yet falling into two main scenarios: active galactic nuclei (i.e., SMBH) or compact star-forming regions. If star-forming, LRD would represent the highest stellar densities ever observed. If SMBH, their high Eddington fractions, and already high masses, help elucidate the growth of the most massive SMBH found by JWST in the early Universe ( z \ensuremath≳ 4 ). In this mini-review, we present the observational evidence accumulated to date, including sub-millimeter probes of LRD dust masses, constraints on radio and X-ray emission from stacking, and rest-frame ultraviolet and optical measurements provided by JWST. Furthermore, we highlight how identifying additional LRD that are truly primarily SMBH-driven may help to shed light on the formation of ’overly massive’ SMBH discovered by JWST within the first billion years since the Big Bang.

@article{2026FrASS..1379045V, author = {{Vaida}, David D. and {Farber}, Ryan Jeffrey}, title = {{Little red dots: the assembly of early supermassive black holes in the JWST Era}}, journal = {Frontiers in Astronomy and Space Sciences}, keywords = {AGN, direct collapse black holes, JWST, little red dots, primordial black holes, super-Eddington accretion, supermassive black holes, supermassive stars}, year = {2026}, month = feb, volume = {13}, eid = {1779045}, pages = {1779045}, doi = {10.3389/fspas.2026.1779045}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026FrASS..1379045V}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, heavy seed, jwst, review, super-eddington}, eprint = {2601.00089}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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Water absorption confirms cool atmospheres in two little red dots

Bingjie Wang, Joel Leja, Ivo Labbe, and 35 more authors

arXiv e-prints, Feb 2026

Abs ADS arXiv

Little red dots (LRDs) are an abundant population of compact high- redshift sources with red rest-frame optical continua, discovered by the James Webb Space Telescope (JWST). Their red colors and power sources have been attributed either to dust reddening of standard hot accretion disks or to intrinsically cool thermal emission from dense hydrogen envelopes, in both cases surrounding accreting supermassive black holes. These scenarios predict order-of-magnitude differences in emission temperature but have lacked decisive temperature diagnostics. Here we report a prominent absorption feature at rest-frame ∼1.4 \,μ\mathrmm in two out of four LRDs at z ∼2 with high signal-to-noise JWST spectra, among the coolest from a large LRD sample. The feature matches the shape and wavelength of the water absorption band seen in cool stars. Atmosphere models require T ≲3000 \mathrmK to reproduce it, confirming unambiguously the presence of a cool, dense gas component contributing 20-30% to the emergent continuum. A composite model reproduces both the absorption and the rest- frame optical-to-infrared continuum shape and suggests a temperature range (\sim2000 \mathrmK - 4000  \mathrmK) rather than a single blackbody predicted by some gas envelope models. Molecular absorption demonstrates that the red continua of some LRDs are intrinsic rather than dust-reddened, implying order-of-magnitude lower bolometric luminosities and black-hole masses, and providing a new diagnostic of the emitting gas.

@article{2026arXiv260206024W, author = {{Wang}, Bingjie and {Leja}, Joel and {Labbe}, Ivo and {Greene}, Jenny E. and {Liu}, Hanpu and {de Graaff}, Anna and {Hviding}, Raphael E. and {Matthee}, Jorryt and {Quataert}, Eliot and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Brammer}, Gabriel and {Burgasser}, Adam J. and {Chen}, Yi-Xian and {Cleri}, Nikko J. and {Cutler}, Sam E. and {Dayal}, Pratika and {Furtak}, Lukas J. and {Fujimoto}, Seiji and {Glazebrook}, Karl and {Goulding}, Andy D. and {Helton}, Jakob M. and {Hirschmann}, Michaela and {Jiang}, Yan-Fei and {Kokorev}, Vasily and {Ma}, Yilun and {Miller}, Tim B. and {Naidu}, Rohan P. and {Oesch}, Pascal and {Pan}, Richard and {Papovich}, Casey and {Price}, Sedona H. and {Rix}, Hans-Walter and {Setton}, David J. and {Sun}, Wendy Q. and {Weaver}, John R. and {Whitaker}, Katherine E. and {Zitrin}, Adi}, title = {{Water absorption confirms cool atmospheres in two little red dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = feb, eid = {arXiv:2602.06024}, pages = {arXiv:2602.06024}, archiveprefix = {arXiv}, eprint = {2602.06024}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260206024W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, jwst, non-agn, sed, spectroscopy}, month_numeric = {2} }

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Limitations on Morphological Fitting for JWST “Little Red Dots”

Kelly E. Whalen, Kimberly A. Weaver, Ryan C. Hickox, and 1 more author

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

Early results from JWST have uncovered a peculiar class of objects referred to as “little red dots” (LRDs). The extremely compact morphologies of these LRDs are often invoked to point towards an active galactic nucleus (AGN)-dominated picture in the context of their conflicting multiwavelength properties. In this work, we assess the capability of pysersic and GALFIT—commonly used tools in LRD morphological studies—to recover input parameters for a simulated suite of LRD-like objects in the F444W band. We find that (1) these tools have difficulty recovering input parameters for simulated images with signal-to-noise ratio (SNR) \ensuremath≲ 25; (2) estimated point-spread function (PSF) fraction could be a more robust physically motivated description of LRD compactness; and (3) almost all permutations of modeled LRDs with SNR \ensuremath≲ 50 cannot be differentiated from a point source, regardless of intrinsic extent. This has serious implications on how we interpret morphological results for increasingly large photometric samples of LRDs, especially at extremely high z or in relatively shallow fields. We present results of Sérsic and two-component fitting to a sample of observed LRDs to compare with our mock sample fitting. We find that \ensuremath∼85% of observed LRDs are PSF dominated, consistent with the AGN-dominated interpretation. The remaining \ensuremath∼15% have low estimated PSF fractions (two-component fit) and sizes \ensuremath≳150 pc (Sérsic fit). This morphological diversity of LRDs suggests that that the population likely is not homogeneous. It possibly has a primary subset of LRDs consistent with the AGN-dominated hypothesis, and a secondary population more consistent with arising perhaps from extremely compact starbursts.

@article{2026ApJ...998..133W, author = {{Whalen}, Kelly E. and {Weaver}, Kimberly A. and {Hickox}, Ryan C. and {Lambrides}, Erini}, title = {{Limitations on Morphological Fitting for JWST ``Little Red Dots''}}, journal = {\apj}, keywords = {Active galaxies, Active galactic nuclei, Starburst galaxies, AGN host galaxies, High-redshift galaxies, 17, 16, 1570, 2017, 734, Astrophysics of Galaxies}, year = {2026}, month = feb, volume = {998}, number = {1}, eid = {133}, pages = {133}, doi = {10.3847/1538-4357/ae31e5}, archiveprefix = {arXiv}, eprint = {2509.21236}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...998..133W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, jwst, morphology, simulation, starburst}, month_numeric = {2} }

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Abundant Population of Broad H\ensuremathα Emitters in the GOODS-N Field Revealed by CONGRESS, FRESCO, and JADES

Junyu Zhang, Eiichi Egami, Fengwu Sun, and 15 more authors

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

We present a spectroscopic search for broad H\ensuremathα emitters at z ≍ 3.7─6.5 in the GOODS-N field, utilizing JWST/NIRCam slitless spectroscopy from FRESCO and CONGRESS, complemented by JADES imaging. We identify 19 broad H\ensuremathα emitters with FWHM > 1000 km s^\ensuremath-1 at z ≍ 4─5.5, including nine new sources. The broad H\ensuremathα luminosity function derived from our sample is consistent with those of other JWST- selected broad-line active galactic nuclei (AGN) reported in the literature. The black hole masses and AGN bolometric luminosities inferred from the broad H\ensuremathα components indicate that most sources are accreting at \ensuremath∼10% of the Eddington limit. We derive their host stellar masses via spectral energy distribution (SED) fitting and find higher M_BH/M_* ratios relative to the local M_BH─M_* relations, consistent with previous studies. We find that 42% of the sample do not satisfy the widely used color selection criteria for little red dots (LRDs), with the majority of these sources lacking the characteristic steep rest-optical red slope, indicating that the LRD selection is highly incomplete when selecting AGN galaxies. A comparison of the average SEDs between our sample and LRDs selected in the same field reveals that the steep red slopes observed in some LRDs are likely due to line-boosting effects as previously suggested. Furthermore, we find that 68% of color-selected LRDs with H\ensuremathα detections in the NIRCam/grism spectra do not exhibit broad-line features. While the limited sensitivity of the grism spectra may hinder the detection of broad-line components in faint sources, our findings still highlight the enigmatic nature of the LRD population.

@article{2026ApJ...997..250Z, author = {{Zhang}, Junyu and {Egami}, Eiichi and {Sun}, Fengwu and {Lin}, Xiaojing and {Lyu}, Jianwei and {Zhu}, Yongda and {Rinaldi}, Pierluigi and {Sun}, Yang and {Bunker}, Andrew J. and {Bhatawdekar}, Rachana and {Helton}, Jakob M. and {Maiolino}, Roberto and {Ma}, Zheng and {Robertson}, Brant and {Tacchella}, Sandro and {Venturi}, Giacomo and {Williams}, Christina C. and {Willott}, Chris}, title = {{Abundant Population of Broad H{\ensuremath{\alpha}} Emitters in the GOODS-N Field Revealed by CONGRESS, FRESCO, and JADES}}, journal = {\apj}, keywords = {AGN host galaxies, Active galactic nuclei, Supermassive black holes, High-redshift galaxies, 2017, 16, 1663, 734}, year = {2026}, month = feb, volume = {997}, number = {2}, eid = {250}, pages = {250}, doi = {10.3847/1538-4357/ae2681}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...997..250Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, agn-dominated, black hole mass, jwst, spectroscopy}, eprint = {2505.02895}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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JWST Insights into Narrow-line Little Red Dots

Zijian Zhang, Linhua Jiang, Weiyang Liu, and 2 more authors

The Astrophysical Journal, Feb 2026

Abs DOI ADS arXiv

JWST has revealed a population of red and compact objects with unique “V-shaped” spectral energy distributions (SEDs) known as “Little Red Dots” (LRDs). Many LRDs exhibit broad Balmer lines and thus likely host active galactic nuclei (AGNs). Here we present a study of five LRDs without broad H\ensuremathα lines at z \ensuremath≥ 5. They are selected from 32 LRDs that have NIRSpec high- or medium- resolution grating spectra covering H\ensuremathα, and their H\ensuremathα line widths are around 250 km s^\ensuremath-1. Compared to normal star-forming galaxies, narrow-line LRDs tend to have relatively higher H\ensuremathα line widths and luminosities. If they are dominated by galaxies, our SED modeling suggests that they are dusty, compact star-forming galaxies with high stellar masses and star formation rates. Alternatively, if their SEDs are produced by AGNs, the inferred black hole masses (<10^6 M_\ensuremath⊙) place them at the low-mass end of the AGN population. They may represent an early stage of super- Eddington growth, where the black holes have yet to accumulate significant masses. With large uncertainties, these black holes appear slightly overmassive relative to the local M_BH─M_*relation, but consistent or undermassive with respect to the M_BH─\ensuremathσ_stellar and M_BH─M_dyn relations. These narrow-line LRDs offer new insights into the diversity of LRDs. Finally, we find that \ensuremath∼44% of high-redshift broad-line AGNs exhibit V-shaped SEDs. In addition, \ensuremath∼20% of the previous LRD candidates are not real LRDs, and their V-shaped SEDs are caused by strong line emission.

@article{2026ApJ...998..170Z, author = {{Zhang}, Zijian and {Jiang}, Linhua and {Liu}, Weiyang and {Ho}, Luis C. and {Inayoshi}, Kohei}, title = {{JWST Insights into Narrow-line Little Red Dots}}, journal = {\apj}, keywords = {AGN host galaxies, Active galaxies, 2017, 17}, year = {2026}, month = feb, volume = {998}, number = {1}, eid = {170}, pages = {170}, doi = {10.3847/1538-4357/ae33c4}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...998..170Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, jwst, sed, spectroscopy, super-eddington}, eprint = {2506.04350}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {2} }

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Origins of the UV continuum and Balmer emission lines in Little Red Dots: observational validation of dense gas envelope models enshrouding the AGN

Yoshihisa Asada, Kohei Inayoshi, Qinyue Fei, and 2 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

We present a statistical study on the origins of the UV continuum and narrow/broad emission lines in little red dots (LRDs), a newly discovered class of active galactic nuclei (AGNs). Leveraging all archived JWST/NIRSpec data, we build a sample of 28 spectroscopically-confirmed LRDs at 5<z_\rm spec<7.2, by requiring broad Hα emission, blue UV colors, V-shaped continua, and compact morphologies. We define a control sample of 9 blue, compact, broad-line AGNs without red optical continua (hereafter little blue dots; LBDs), and examine correlations between rest UV and the narrow/broad Hα luminosities in these populations. In LRDs, both narrow and broad Hα components are tightly correlated with the UV continuum, and the luminosity ratios are consistent with those in young starburst galaxies. In contrast, the UV to broad Hα ratios in LBDs closely match local unobscured AGNs and are statistically different from LRDs. The Lyα occurrence rates and strengths do not differ between LRDs and LBDs and are comparable to normal star-forming galaxies. These results are consistent with a scenario where the central BH in LRDs is enshrouded by a dense opaque gas envelope – in this model, the UV continuum as well as narrow and even broad Hα emissions are not powered by AGNs but predominantly by young massive stars surrounding the envelope, while the envelope radiates as a ∼5000 K blackbody. As the envelope dissipates, direct AGN emission can emerge, potentially transforming LRDs into LBDs and marking the end of a short-lived phase of rapid black hole growth.

@article{2026arXiv260110573A, author = {{Asada}, Yoshihisa and {Inayoshi}, Kohei and {Fei}, Qinyue and {Fujimoto}, Seiji and {Willott}, Chris}, title = {{Origins of the UV continuum and Balmer emission lines in Little Red Dots: observational validation of dense gas envelope models enshrouding the AGN}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jan, eid = {arXiv:2601.10573}, pages = {arXiv:2601.10573}, archiveprefix = {arXiv}, eprint = {2601.10573}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260110573A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, sed, starburst}, month_numeric = {1} }

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Little Red Dots and Supermassive Black Hole Seed Formation in Ultralight Dark Matter Halos

Dongsu Bak and Jae-Weon Lee

arXiv e-prints, Jan 2026

Abs DOI ADS arXiv

We investigate how supermassive black hole (SMBH) seeds form in the early Universe at the centers of ultralight dark matter (ULDM) halos. Focusing on the ULDM Jeans scale, we identify the critical conditions under which high-redshift baryonic gas, strongly confined by central solitonic cores of the halos, undergoes direct and monolithic collapse. The solitonic potential naturally drives rapid inflow and shock heating, allowing the gas to exceed the critical atomic-cooling and fragmentation-suppression threshold of ∼3 \times 10^4 \rm K without invoking an external UV background. We derive semi- analytic relations for the halo mass, soliton mass, baryonic core radius, and thermodynamic state of the gas, including the effects of baryonic contraction. These relations simultaneously determine the minimum and maximum SMBH seed masses as functions of redshift. In this framework, pristine gas clouds that satisfy the temperature threshold collapse without fragmentation, forming SMBH seeds with characteristic masses of order ∼10^5M_⊙, while systems below the threshold are expected to form compact star clusters instead. Our model also implies an upper limit on the attainable SMBH mass, predicting a maximum mass scale of order \sim10^10M_⊙, consistent with the most massive quasars observed to date. The ULDM particle mass required to reproduce the inferred seed mass scale, m ≃10^-22\rm eV, coincides with the value favored by galactic- scale observations, providing a unified explanation for the characteristic masses of both galactic cores and early SMBH seeds. Our model predicts efficient SMBH seed formation at redshifts z rsim 10 and offers a natural interpretation of recently observed little red dots as SMBHs embedded in compact, hot, ionized gas clouds.

@article{2026arXiv260121676B, author = {{Bak}, Dongsu and {Lee}, Jae-Weon}, title = {{Little Red Dots and Supermassive Black Hole Seed Formation in Ultralight Dark Matter Halos}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jan, eid = {arXiv:2601.21676}, pages = {arXiv:2601.21676}, doi = {10.48550/arXiv.2601.21676}, archiveprefix = {arXiv}, eprint = {2601.21676}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260121676B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, exotic physics, super-eddington, theory}, month_numeric = {1} }

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A Comprehensive Photometric Selection of “Little Red Dots” in MIRI Fields: An Infrared-Bright Little Red Dot at z = 3.1386 with Warm Dust Emission

Guillermo Barro, Pablo G. Pérez-González, Dale D. Kocevski, and 13 more authors

The Astrophysical Journal, Jan 2026

Abs DOI ADS arXiv

JWST has revealed a population of compact “Little Red Dots” (LRDs) at z \ensuremath≳ 4, with red rest-frame optical and blue UV colors. These objects are likely compact dusty starbursts or heavily reddened AGNs, playing a pivotal role in early black hole growth, dust production, and stellar assembly. We introduce a new photometric selection to identify LRDs over a broad range in redshifts and rest-frame UV to near-IR (NIR) colors enabling a more complete census of the population. This method identifies 248 LRDs with F444W 6 \ensuremathμm and peaks near \ensuremath∼40 \ensuremathμm, providing the first direct evidence of warm dust emission (T = 50─100 K) in an LRD.

@article{2026ApJ...997...48B, author = {{Barro}, Guillermo and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Kocevski}, Dale D. and {McGrath}, Elizabeth J. and {Leung}, Gene C. K. and {Cullen}, Fergus and {Dunlop}, James S. and {Ellis}, Richard S. and {Finkelstein}, Steven L. and {Grogin}, Norman A. and {Illingworth}, Garth and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Lucas}, Ray A. and {McLure}, Ross J. and {Yang}, Guang}, title = {{A Comprehensive Photometric Selection of ``Little Red Dots'' in MIRI Fields: An Infrared-Bright Little Red Dot at z = 3.1386 with Warm Dust Emission}}, journal = {\apj}, keywords = {AGN host galaxies, Compact galaxies, High-redshift galaxies, Infrared excess galaxies, 2017, 285, 734, 789}, year = {2026}, month = jan, volume = {997}, number = {1}, eid = {48}, pages = {48}, doi = {10.3847/1538-4357/ae0704}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...997...48B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, photometry, sample selection, sed}, eprint = {2412.01887}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Little Red Dots as Late-stage Quasi-stars

Mitchell C. Begelman and Jason Dexter

The Astrophysical Journal, Jan 2026

Abs DOI ADS arXiv

We argue that the “Little Red Dots” (LRDs) discovered with the James Webb Space Telescope are quasi-stars in their late stages of evolution. Quasi-stars are hypothetical objects predicted to form following the core collapse of supermassive stars and consist of black holes (BHs) accreting from massive envelopes at a super-Eddington rate. We show that models of late-stage quasi- stars, with BH masses exceeding \ensuremath∼10% of the total, predict thermal and radiative properties that are insensitive to both BH and envelope mass and spectrally resemble LRDs. Specifically, we show that they are likely to exhibit reddish colors, a strong Balmer break, and possess conditions favorable to the production of Balmer lines that are broadened by electron scattering. Their huge electron column densities suppress any X-rays. Late-stage quasi-stars, with BH masses \ensuremath≳10^6 M_\ensuremath⊙, should dominate the overall quasi-star population. Their short predicted lifetimes (tens of Myr), coupled with the high observed comoving density of LRDs, suggest that most or all supermassive BHs go through a quasi-star/LRD phase during their formation and growth.

@article{2026ApJ...996...48B, author = {{Begelman}, Mitchell C. and {Dexter}, Jason}, title = {{Little Red Dots as Late-stage Quasi-stars}}, journal = {\apj}, keywords = {Accretion, Active galactic nuclei, High-redshift galaxies, Quasars, Supermassive black holes, 14, 16, 734, 1319, 1663}, year = {2026}, month = jan, volume = {996}, number = {1}, eid = {48}, pages = {48}, doi = {10.3847/1538-4357/ae274a}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...996...48B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, sed, theory}, eprint = {2507.09085}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Investigating the growth of little red dot descendants at z < 4 with the JWST

Jean-Baptiste Billand, David Elbaz, Fabrizio Gentile, and 16 more authors

Astronomy & Astrophysics, Jan 2026

Abs DOI ADS arXiv

Context. One of the most remarkable and unexpected results of the James Webb Space Telescope is the discovery of a population of compact red galaxies: the so-called little red dots (LRDs). The existence of these galaxies raises many questions, including that of their nature and origin, as well as that of their evolution. Indeed, these compact red sources exhibit a pronounced decline in number density by nearly two orders of magnitude from z = 6 to z = 3. Aims. In this paper, we investigate the possible evolution of this galaxy population at a lower redshift. To this end, we have identified a sample of candidates in the CEERS images that could represent the descendants of LRDs by assuming a single evolutionary path: the development of a blue star-forming outskirt while retaining a inner red core. Methods. Our color─magnitude selection identifies red galaxies as red as LRDs at z < 4, defined by a compact, red, inner region and blue outskirts. The red core is associated with the LRD population, while the blue periphery traces recently formed young stars. Morphological properties were derived by fitting single Sérsic profiles, while other physical quantities were obtained through spectral energy distribution (SED) fitting, assuming a stellar-only model for both the inner region and the outskirts. Results. The selected galaxies are likely “post-LRDs” galaxies, showing similar properties to LRDs under a stellar-only model: stellar masses of M_* ≍ 10^10 M_\ensuremath⊙, central densities \ensuremathΣ_* ≍ 10^11 M_\ensuremath⊙ kpc^\ensuremath-2, similar rest-frame red colors, and a \ensuremath∼1 kpc offset below the size─mass relation. Their number density at z = 3 \ensuremath\pm 0.5 (10^\ensuremath-4.15 Mpc^\ensuremath-3) matches that of LRDs at 5 < z < 7, supporting an evolutionary connection. We find a strong redshift-dependent increase in both outskirts’ mass fraction and galaxy size, from \ensuremath∼250 pc at z = 5 to \ensuremath∼600 pc at z = 3, indicating overall stellar growth. Meanwhile, the core remains as red and as massive, but the characteristic V shaped SED fades as the extended star- forming envelope becomes dominant. Conclusions. These findings support an evolutionary scenario in which LRDs gradually acquire an extended stellar component over cosmic time by cold accretion. This growth affects the initial LRD state in two key ways: the physical size increases and the characteristic V shaped SED in the core becomes less distinct and disappears. As a result, the original selection criteria based on both of them can no longer identify this population as it evolves, providing an explanation for their observed decline in number density.

@article{2026A&A...706A..29B, author = {{Billand}, Jean-Baptiste and {Elbaz}, David and {Gentile}, Fabrizio and {Tarrasse}, Maxime and {Franco}, Maximilien and {Magnelli}, Benjamin and {Daddi}, Emanuele and {Lyu}, Yipeng and {Dekel}, Avishai and {Pacucci}, Fabio and {Sangalli}, Valentina and {Dickinson}, Mark and {Giavalisco}, Mauro and {Holwerda}, Benne W. and {Kocevski}, Dale D. and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Lucas}, Ray A. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G.}, title = {{Investigating the growth of little red dot descendants at z < 4 with the JWST}}, journal = {\aap}, keywords = {galaxies: evolution, galaxies: formation, galaxies: high-redshift, galaxies: structure}, year = {2026}, month = jan, volume = {706}, eid = {A29}, pages = {A29}, doi = {10.1051/0004-6361/202556303}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...706A..29B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, jwst, morphology, non-agn, sed}, eprint = {2507.04011}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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The Little Blue and Red Dots Rosetta Stones: Non-Gaussian broad lines, hot dust, and X-ray weakness

M. Brazzini, F. D’Eugenio, R. Maiolino, and 31 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

The population of Active Galactic Nuclei (AGN) newly discovered by the James Webb Space Telescope (JWST) exhibits peculiar properties that distinguish it from both local type I AGN and high-redshift quasars. Most of these sources are compact, appearing as ’little dots’: among them, the sub-class (10-30% of the total) characterized by significantly red optical colors has been named ’Little Red Dots’ (LRDs), while here we analogously introduce the term ’Little Blue Dots’ (LBDs) for the remaining, bluer sources (70-90%). We then present a comparative analysis of the prototypical representatives (’Rosetta Stones’) of the two classes: GN-28074 at z=2.26, the Red Rosetta Stone, and GS-3073 at z=5.55, the Blue Rosetta Stone. In both Rosetta Stones the broad Balmer lines are better described by exponential profiles rather than single Gaussians, similarly to normal low-redshift type I AGN, indicating that exponential profiles are not unique to LRDs. They are both extremely X-ray weak, show strong auroral [OIII] 4363 emission, weak hot dust mid-IR emission, and no time variability. However, they differ in terms of excitation diagnostics: the HeII 4686 line is undetected in the Red Rosetta but strongly detected in the Blue Rosetta in both narrow and broad components, with the latter much broader than hydrogen Balmer lines. This supports BLR stratification and disfavors the cocoon electron-scattering scenario. An additional difference is the presence of prominent Balmer absorption in the Red Rosetta – indicative of extremely dense gas along the line of sight – but absent in the Blue Rosetta. Taken together, these results suggest that LRDs and LBDs share the same central engine as standard type I AGN, while differing in the amount and geometry of dense gas surrounding the accretion disk, and/or in their accretion properties.

@article{2026arXiv260122214B, author = {{Brazzini}, M. and {D'Eugenio}, F. and {Maiolino}, R. and {Lyu}, J. and {DeCoursey}, C. and {{\"U}bler}, H. and {Ji}, X. and {Juod{\v{z}}balis}, I. and {Scholtz}, J. and {Jones}, G. C. and {Hainline}, K. and {Dalla Bont{\`a}}, E. and {{\'e}rez-Gonz{\'a}lez}, P. G. P and {Geris}, S. and {Harshan}, A. and {Feruglio}, C. and {Bischetti}, M. and {Mazzolari}, G. and {Rieke}, G. and {Alberts}, S. and {Trefoloni}, B. and {Carniani}, S. and {Parlanti}, E. and {Marconi}, A. and {Risaliti}, G. and {Ramos Almeida}, C. and {Rinaldi}, P. and {Perna}, M. and {Zamora}, S. and {Lamperti}, I. and {Venturi}, G. and {Cresci}, G. and {Bunker}, Andrew J. and {Ivey}, L. R.}, title = {{The Little Blue and Red Dots Rosetta Stones: Non-Gaussian broad lines, hot dust, and X-ray weakness}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jan, eid = {arXiv:2601.22214}, pages = {arXiv:2601.22214}, archiveprefix = {arXiv}, eprint = {2601.22214}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260122214B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, emission lines, jwst, x-ray}, month_numeric = {1} }

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Pseudo Little Red Dot: an Active Black Hole Embedded in a Dense and Dusty, Metal-Poor Starburst Galaxy at z=5.96

Karina I. Caputi, Ryan A. Cooper, Pierluigi Rinaldi, and 2 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

We present a study of Pseudo-LRD-NOM (Pseudo little red dot with no metal lines), a highly magnified low-mass galaxy behind the lensing cluster Abell 370 at z=5.96. We classify this object as a pseudo-LRD because its red rest-frame optical colour is mainly driven by a prominent Halpha line (with EW0 >\raisebox-0.5ex~800 Angstroms) present in its JWST NIRSpec spectrum. Halpha is dominated by a narrow component and also has a minor broad component indicative of an active black hole with M_BH = 2.9x10\^6 Msun. A narrow Hbeta emission line is also detected (with S/N = 8), producing a Balmer decrement (narrow) Halpha/Hbeta = 11. The rest-frame UV spectral slope is beta_UVspec = -1.2. All these features can be ascribed to high dust attenuation. However, no [OIII]5007 or any other metal lines are detected in the spectrum, so [OIII]5007/Hbeta \raisebox-0.5ex~10\^6 cm\^{-3}) and extremely low gas/stellar metallicities (Z = 0.01-0.1 Zsun). The demagnified stellar mass is 1.62\^{+1.54}_{-0.79} x10\^7 Msun and the stellar-mass surface density is Sigma* = 418\^{+725}_{-310} Msun/pc\^2, similar to that of massive/nuclear star clusters. Pseudo-LRD-NOM provides evidence of massive black-hole growth occurring in a high-density, dusty starburst which is at the early stages of its chemical enrichment, and is likely a precursor to a real LRD.

@article{2026arXiv260111466C, author = {{Caputi}, Karina I. and {Cooper}, Ryan A. and {Rinaldi}, Pierluigi and {Navarro-Carrera}, Rafael and {Iani}, Edoardo}, title = {{Pseudo Little Red Dot: an Active Black Hole Embedded in a Dense and Dusty, Metal-Poor Starburst Galaxy at z=5.96}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = jan, eid = {arXiv:2601.11466}, pages = {arXiv:2601.11466}, archiveprefix = {arXiv}, eprint = {2601.11466}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260111466C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, jwst, spectroscopy, starburst}, month_numeric = {1} }

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Rapid emergence of overmassive black holes in the early Universe

Sunmyon Chon, Shingo Hirano, Tomoaki Ishiyama, and 2 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

The origin of supermassive black holes (SMBHs) remains a long-standing problem in astrophysics. Recent JWST observations reveal an unexpectedly abundant population of overmassive black holes at z>4-6, where the BH masses lie far above local scaling relations and not reproduced by current cosmological models. How such overmassive black holes form and rapidly grow within young galaxies has remained unclear. Here we present fully cosmological radiation-hydrodynamic simulations that, for the first time, self-consistently follow the birth, early growth, and emergent observable signatures of SMBHs in proto-cluster environments. We find that heavy seeds of order 10^6 M_\textsun naturally form, exceeding typical theoretical expectations by an order of magnitude. These seeds rapidly develop dense, optically thick disks whose strong electron scattering produces broad Hα emission comparable to that seen in little red dots (LRDs). Sustained super-Eddington accretion then drives fast growth to ∼3 \times 10^7 ~M_\textsun by z ∼8. These results provide a unified physical scenario in which LRDs correspond to a short-lived, enshrouded phase of heavy-seed formation, naturally evolving into the overmassive quasars detected by JWST and ultimately the progenitors of today’s SMBHs.

@article{2026arXiv260104955C, author = {{Chon}, Sunmyon and {Hirano}, Shingo and {Ishiyama}, Tomoaki and {Chang}, Seok-Jun and {Springel}, Volker}, title = {{Rapid emergence of overmassive black holes in the early Universe}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, Solar and Stellar Astrophysics}, year = {2026}, month = jan, eid = {arXiv:2601.04955}, pages = {arXiv:2601.04955}, archiveprefix = {arXiv}, eprint = {2601.04955}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260104955C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, simulation}, month_numeric = {1} }

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JADES and BlackTHUNDER: rest-frame Balmer-line absorption and the local environment in a Little Red Dot at z = 5

Francesco D’Eugenio, Ignas Juodžbalis, Xihan Ji, and 33 more authors

Monthly Notices of the Royal Astronomical Society, Jan 2026

Abs DOI ADS arXiv

We present a ’Little Red Dot’ (LRD) broad-line active galactic nucleus (AGN) at , observed with NIRSpec/MSA (micro-shutter assembly) and NIRSpec/IFU (integral-field unit) by the JADES (JWST Advanced Deep Extragalactic Survey) and BlackTHUNDER (Black holes in THe early Universe aNd their DensE surRoundings) surveys. Combining spatially resolved and high-resolution spectroscopy, we characterize its central engine, host, and environment. H has multiple components, including two broad Gaussians, yielding a black-hole mass , while [O III]5007 gives a galaxy dynamical mass , suggesting an overmassive black hole relative to the host galaxy. The target is immersed in a 7-kpc wide pool of ionized gas and has three neighbours: a satellite galaxy, a possible satellite/gas cloud, and a tentatively detected spatially detached outflow. H shows strong, rest-frame absorption, deeper than the continuum, ruling out a stellar origin. The velocity and velocity dispersion are and . There is tentative evidence (2.6\ensuremathσ) of temporal variability in the equivalent width of the H absorber over two rest-frame months, suggesting a highly dynamic nucleus. Notably, while the H absorber is clearly visible and even dominant in the high-resolution G395H observations, it is not detected in the medium-resolution G395M data of the same epoch. This implies that the current incidence rate of absorbers in LRDs ─ and especially of rest-frame absorbers ─ may be severely underestimated, because most LRDs rely on lower resolution spectroscopy. The high incidence rate of rest-frame absorbers in LRDs may indicate a configuration that is either intrinsically stationary, such as a rotating disc, or that exhibits time- averaged stability, such as an oscillatory ’breathing mode’ accretion with cyclic expansion and contraction of the gas around the supermassive black hole.

@article{2026MNRAS.545f2117D, author = {{D'Eugenio}, Francesco and {Juod{\v{z}}balis}, Ignas and {Ji}, Xihan and {Scholtz}, Jan and {Maiolino}, Roberto and {Carniani}, Stefano and {Perna}, Michele and {Mazzolari}, Giovanni and {{\"U}bler}, Hannah and {Arribas}, Santiago and {Bhatawdekar}, Rachana and {Bunker}, Andrew J. and {Cresci}, Giovanni and {Curtis-Lake}, Emma and {Hainline}, Kevin and {Inayoshi}, Kohei and {Isobe}, Yuki and {Ji}, Zhiyuan and {Johnson}, Benjamin D. and {Jones}, Gareth C. and {Looser}, Tobias J. and {Nelson}, Erica J. and {Parlanti}, Eleonora and {Pusk{\'a}s}, D{\'a}vid and {Rinaldi}, Pierluigi and {Robertson}, Brant and {Rodr{\'\i}guez Del Pino}, Bruno and {Shivaei}, Irene and {Sun}, Fengwu and {Tacchella}, Sandro and {Venturi}, Giacomo and {Volonteri}, Marta and {Williams}, Christina C. and {Willmer}, Christopher N. A. and {Willott}, Chris and {Witstok}, Joris}, title = {{JADES and BlackTHUNDER: rest-frame Balmer-line absorption and the local environment in a Little Red Dot at z = 5}}, journal = {\mnras}, keywords = {galaxies: active, quasars: supermassive black holes, galaxies: Seyfert}, year = {2026}, month = jan, volume = {545}, number = {3}, eid = {staf2117}, pages = {staf2117}, doi = {10.1093/mnras/staf2117}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.545f2117D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, spectroscopy, variability}, eprint = {2506.14870}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Hedorah, the first yellow supergiant Kaiju star candidate at z\approx3 revealed by behind AS1063

J. M. Diego, J. M. Palencia, C. Goolsby, and 6 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

We present a new free-form lens model for the z=0.348 galaxy cluster AS1063, based on previously spectroscopically confirmed lensed galaxies and new images from the GLIMPSE program. We use the ultra-deep data to identify new counterimages for previously confirmed (spectroscopically) lensed systems. We use the full set of spectroscopically confirmed systems to derive a new lens model, which is later used to confirm many of the previous lensed system candidates and discover new lensed system candidates in the images. We compute the geometric redshifts, time delays, and magnification for all counterimages (confirmed and not confirmed). Among the new systems we find a peculiar multiply lensed galaxy with a strong emission line at ≈4\,μm that likely corresponds to H-β and/or OIII at z≈7.5. This galaxy could be a little-red-dot or an extreme emission line galaxy. We also identify a yellow supergiant lensed star candidate at z≈3.1. This star shows some similarities with previous Kaiju stars and we nickname it “Hedorah”, in honor of the famous yellow-eyed Kaiju. Previous lensed stars at z>0.1 are either blue supergiants or red supergiants, making Hedorah the first yellow supergiant discovered beyond z=0.1 and confirming that, despite their rarity, they can also be found at these redshifts. Since many Cepheid stars are yellow supergiants, we consider the possibility that Hedorah could also be the first Cepheid discovered at cosmological distances, but we conclude that Hedorah is more likely a hypergiant yellow star approaching the end of its life. Alternatively, Hedorah could be a small group of stars, although this is less likely based on Hedorah’s peculiar colors and additionally may require the more exotic fuzzy dark matter to help explain the lack of counterimage.

@article{2026arXiv260111704D, author = {{Diego}, J. M. and {Palencia}, J. M. and {Goolsby}, C. and {Conselice}, C. J. and {Lagattuta}, D. J. and {Mahler}, G. and {Richard}, J. and {Sharon}, K. and {Williams}, L. L. R.}, title = {{Hedorah, the first yellow supergiant Kaiju star candidate at $z\approx3$ revealed by behind AS1063}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, Solar and Stellar Astrophysics}, year = {2026}, month = jan, eid = {arXiv:2601.11704}, pages = {arXiv:2601.11704}, archiveprefix = {arXiv}, eprint = {2601.11704}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260111704D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, non-agn, non-jwst, spectroscopy}, month_numeric = {1} }

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What You See Is What You Get: Empirically Measured Bolometric Luminosities of Little Red Dots

Jenny E. Greene, David J. Setton, Lukas J. Furtak, and 27 more authors

The Astrophysical Journal, Jan 2026

Abs DOI ADS arXiv

New populations of red active galactic nuclei (known as “little red dots”) discovered by JWST exhibit remarkable spectral energy distributions. Leveraging X-ray through far-infrared observations of two of the most luminous known little red dots, we directly measure their bolometric luminosities. We find evidence that more than half of the bolometric luminosity likely emerges in the rest-frame optical, with L_bol/L_5100 = 5, roughly half the value for “standard” active galactic nuclei. Meanwhile, the X-ray emitting corona, UV-emitting blackbody, and reprocessed mid to far-infrared emission are all considerably subdominant, assuming that the far-infrared luminosity is well below current measured limits. We present new bolometric corrections that dramatically lower inferred bolometric luminosities by a factor of 10 compared to published values in the literature. These bolometric corrections are in accord with expectations from models in which gas absorption and reprocessing are responsible for the red rest-frame optical colors of little red dots. We discuss how this lowered luminosity scale suggests a lower mass scale for the population by at least an order of magnitude (e.g., \ensuremath∼10^5─10^7 M_\ensuremath⊙ black holes, and \ensuremath∼10^8 M_\ensuremath⊙ galaxies), alleviating tensions with clustering, overmassive black holes, and the integrated black hole mass density in the Universe.

@article{2026ApJ...996..129G, author = {{Greene}, Jenny E. and {Setton}, David J. and {Furtak}, Lukas J. and {Naidu}, Rohan P. and {Volonteri}, Marta and {Dayal}, Pratika and {Labbe}, Ivo and {van Dokkum}, Pieter and {Bezanson}, Rachel and {Brammer}, Gabriel and {Cutler}, Sam E. and {Glazebrook}, Karl and {de Graaff}, Anna and {Hirschmann}, Michaela and {Hviding}, Raphael E. and {Kokorev}, Vasily and {Leja}, Joel and {Liu}, Hanpu and {Ma}, Yilun and {Matthee}, Jorryt and {Nanayakkara}, Themiya and {Oesch}, Pascal A. and {Pan}, Richard and {Price}, Sedona H. and {Spilker}, Justin S. and {Wang}, Bingjie and {Weaver}, John R. and {Whitaker}, Katherine E. and {Williams}, Christina C. and {Zitrin}, Adi}, title = {{What You See Is What You Get: Empirically Measured Bolometric Luminosities of Little Red Dots}}, journal = {\apj}, keywords = {Active galactic nuclei, High-redshift galaxies, Supermassive black holes, 16, 734, 1663}, year = {2026}, month = jan, volume = {996}, number = {2}, eid = {129}, pages = {129}, doi = {10.3847/1538-4357/ae1836}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...996..129G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, jwst, multi-wavelength, sed, x-ray}, eprint = {2509.05434}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Supermassive Dark Stars and Their Remnants as a Possible Solution to Three Recent Cosmic Dawn Puzzles

Cosmin Ilie, Jillian Paulin, Andreea Petric, and 1 more author

Universe, Jan 2026

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has begun to revolutionize our view of the Cosmos. The discovery of Blue Monsters (i.e., ultra- compact yet very bright high-z galaxies) and the Little Red Dots (i.e., very compact dustless strong Balmer break cosmic dawn sources) pose significant challenges to pre-JWST era models of the assembly of first stars and galaxies. In addition, JWST data further strengthen the problem posed by the origin of the supermassive black holes that power the most distant quasars observed. Stars powered by Dark Matter annihilation (i.e., Dark Stars) can form out of primordial gas clouds during the cosmic dawn era and subsequently might grow via accretion and become supermassive. In this paper we argue that Supermassive Dark Stars (SMDSs) offer natural solutions to the three puzzles mentioned above.

@article{2026Univ...12....1I, author = {{Ilie}, Cosmin and {Paulin}, Jillian and {Petric}, Andreea and {Freese}, Katherine}, title = {{Supermassive Dark Stars and Their Remnants as a Possible Solution to Three Recent Cosmic Dawn Puzzles}}, journal = {Universe}, keywords = {Dark Matter (DM), Dark Stars (DSs), high-z galaxies, supermassive black holes (SMBHs), little red dots (LRDs), blue monsters, over-massive BH galaxies (OBGs)}, year = {2026}, month = jan, volume = {12}, number = {1}, eid = {1}, pages = {1}, doi = {10.3390/universe12010001}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026Univ...12....1I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, exotic physics, jwst, super-eddington, theory}, eprint = {2511.08477}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Formation of the Little Red Dots from the Core Collapse of Self-interacting Dark Matter Halos

Fangzhou Jiang, Zixiang Jia, Haonan Zheng, and 5 more authors

The Astrophysical Journal Letters, Jan 2026

Abs DOI ADS arXiv

We present a statistical study of black hole (BH) formation and growth seeded by gravothermal core collapse of self-interacting dark matter (SIDM) halos at high redshift, using a cosmological semianalytical framework based on Monte Carlo merger trees. We demonstrate that gravothermal collapse naturally leads to BH formation in high-concentration halos at a characteristic mass scale set by the SIDM cross section and occurs predominantly in the early Universe. This mechanism is particularly promising for explaining the abundance of the little red dots (LRDs)—early active galactic nuclei whose BHs appear dramatically overmassive relative to their host galaxies. By incorporating this seeding process with simple models of BH growth and assuming a 100% duty cycle, we broadly reproduce the observed LRD mass function for velocity-dependent cross sections of \ensuremathσ_0m \ensuremath∼ 30 cm^2 g^\ensuremath-1 and \ensuremathω \ensuremath∼ 80 km s^\ensuremath-1, which are consistent with independent constraints from local galaxies. While higher values of \ensuremathσ_0m (or \ensuremathω) would overpredict the low-mass (or high- mass) end of the BH mass function, such deviations could be reconciled by invoking a reduced duty cycle or lower Eddington ratio. Our results suggest that the demographics of high- redshift BHs can serve as a novel and complementary probe of SIDM physics.

@article{2026ApJ...996L..19J, author = {{Jiang}, Fangzhou and {Jia}, Zixiang and {Zheng}, Haonan and {Ho}, Luis C. and {Inayoshi}, Kohei and {Shen}, Xuejian and {Vogelsberger}, Mark and {Feng}, Wei-Xiang}, title = {{Formation of the Little Red Dots from the Core Collapse of Self-interacting Dark Matter Halos}}, journal = {\apjl}, keywords = {Dark matter, Supermassive black holes, Galaxy dark matter halos, Early universe, 353, 1663, 1880, 435}, year = {2026}, month = jan, volume = {996}, number = {1}, eid = {L19}, pages = {L19}, doi = {10.3847/2041-8213/ae247a}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...996L..19J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, non-agn, simulation, theory}, eprint = {2503.23710}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Lord of LRDs: insights into a ’Little Red Dot’ with a low-ionization spectrum at z = 0.1

Xihan Ji, Francesco D’Eugenio, Ignas Juodžbalis, and 14 more authors

Monthly Notices of the Royal Astronomical Society, Jan 2026

Abs DOI ADS arXiv

Recent observations by the James Webb Space Telescope (JWST) have revealed a puzzling population of optically red and compact galaxies with peculiar ’V’-shaped spectra at high redshift, known as ’Little Red Dots’ (LRDs). Until now, most spectroscopically confirmed LRDs are found at and it has been speculated that LRDs are tracing the early stages of black hole evolution. We report an independent rediscovery of a broad-line active galactic nucleus (AGN), SDSS J102530.29+140207.3, at , which shows spectral features matching those of LRDs seen in the early Universe, including the V-shaped spectrum, broad Balmer lines (with widths of 1000─2000 ), and deep Balmer absorption. We present a new GTC observation of this LRD, which reveals an optical continuum similar to those of G-to-K giant stars including an unambiguous G-band absorption originating from the CH molecule. In addition, this local LRD shows a series of absorption lines potentially related to low-ionization ions or atoms but are deeper than what is observed in empirical stellar templates. We further identify a series of [Fe II] emission lines indicative of low-ionization gas, which we find also present in a JWST-selected LRD at . We find small but statistically significant variability in the H of SDSS J102530.29+140207.3 consistent with previous findings. Finally, we report new observations with NuSTAR. We confirm the extreme X-ray weakness of this LRD, which might imply Compton-thick gas obscuration with . All evidence suggests SDSS J102530.29+140207.3 has a complex gaseous environment and the strong ionic, atomic, and molecular absorptions are hard to explain with typical stellar and AGN models.

@article{2026MNRAS.545f2235J, author = {{Ji}, Xihan and {D'Eugenio}, Francesco and {Juod{\v{z}}balis}, Ignas and {Walton}, Dominic J. and {Fabian}, Andrew C. and {Maiolino}, Roberto and {Ramos Almeida}, Cristina and {Acosta Pulido}, Jose A. and {Belokurov}, Vasily A. and {Isobe}, Yuki and {Jones}, Gareth and {Maraston}, Claudia and {Scholtz}, Jan and {Simmonds}, Charlotte and {Tacchella}, Sandro and {Terlevich}, Elena and {Terlevich}, Roberto}, title = {{Lord of LRDs: insights into a 'Little Red Dot' with a low-ionization spectrum at z = 0.1}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: dwarf, Astrophysics of Galaxies}, year = {2026}, month = jan, volume = {545}, number = {3}, eid = {staf2235}, pages = {staf2235}, doi = {10.1093/mnras/staf2235}, archiveprefix = {arXiv}, eprint = {2507.23774}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.545f2235J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, local counterpart, spectroscopy, variability, x-ray}, month_numeric = {1} }

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Signatures of exploding supermassive PopIII stars at high redshift in JWST, EUCLID, and Roman Space Telescope

Cédric Jockel, Kyohei Kawaguchi, Sho Fujibayashi, and 1 more author

Monthly Notices of the Royal Astronomical Society, Jan 2026

Abs DOI ADS arXiv

Recently discovered supermassive black holes with masses of at redshifts ─11 in active galactic nuclei (AGNs) pose severe challenges to our understanding of supermassive black hole formation. One proposed channel are rapidly accreting supermassive PopIII stars (SMSs) that form in large primordial gas haloes and grow up to . They eventually collapse due to the general relativistic instability and could lead to supernova- like explosions. This releases massive and energetic ejecta that then interact with the halo medium via an optically thick shock. We develop a semi-analytic model to compute the shock properties, bolometric luminosity, emission spectrum, and photometry over time. The initial data are informed by stellar evolution and general relativistic SMS collapse simulations. We find that SMS explosion light curves reach a brightness and last 10─200 yr in the source frame ─ up to 250─3000 yr with cosmic time dilation. This makes them quasi-persistent sources which vary indistinguishably to little red dots and AGN within 0.5─ yr. Bright SMS explosions are observable in long-wavelength JWST (James Webb Space Telescope) filters up to (24─26 mag) and pulsating SMSs up to . EUCLID and the Roman Space Telescope (RST) can detect SMS explosions at ─12. Their deep fields could constrain the SMS rate down to Mpcyr, which is much deeper than JWST bounds. Based on cosmological simulations and observed star formation rates, we expect to image up to several hundred SMS explosions with EUCLID and dozens with RST deep fields.

@article{2026MNRAS.545f1949J, author = {{Jockel}, C{\'e}dric and {Kawaguchi}, Kyohei and {Fujibayashi}, Sho and {Shibata}, Masaru}, title = {{Signatures of exploding supermassive PopIII stars at high redshift in JWST, EUCLID, and Roman Space Telescope}}, journal = {\mnras}, keywords = {radiation: dynamics, stars: Population III, quasars: supermassive black holes, dark ages, reionization, first stars, early Universe, transients: supernovae}, year = {2026}, month = jan, volume = {545}, number = {2}, eid = {staf1949}, pages = {staf1949}, doi = {10.1093/mnras/staf1949}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.545f1949J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, non-agn, photometry, simulation}, eprint = {2507.15556}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, month_numeric = {1} }

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The Properties of Little Red Dot Galaxies in the ASTRID Simulation

Patrick LaChance, Rupert A. C. Croft, Tiziana Di Matteo, and 5 more authors

The Open Journal of Astrophysics, Jan 2026

Abs DOI ADS arXiv

We present simulated counterparts of the “Little Red Dot” (LRD) galaxies observed with JWST, using the large cosmological hydrodynamic simulation, ASTRID. We create mock observations of the galaxies ( 5\ensuremath≤z\ensuremath≤8) in ASTRID, and find seventeen which fit the color and size criteria of LRDs. These LRDs are galaxies with high stellar masses (), and massive black holes (). The host galaxies are dense, with stellar half mass radii (), and dust attenuation in the F444W band above 1.25. Their star formation has been recently quenched. They host relatively bright AGN that are dust-obscured and contribute significantly to the rest-frame optical red slope and have relatively low luminosity in the rest-frame ultraviolet, where the host galaxy’s stars are more dominant. These LRDs are in an evolutionary phase of miniquenching that is the result of AGN feedback from their massive black holes. The LRDs in ASTRID are bright with F444W magnitudes of 23.5\ensuremath-25.5. The less massive and fainter galaxies in ASTRID lack the dust concentration necessary to produce the red slope of an LRD, though this could be an effect of limited resolution. Most of the highest Eddington black holes are not LRDs due to insufficient dust attenuation from their host galaxies, which are also experiencing relatively high star formation rates. This results in their spectra being too flat, despite their highly accreting black holes.

@article{2026OJAp....955493L, author = {{LaChance}, Patrick and {Croft}, Rupert A. C. and {Matteo}, Tiziana Di and {Zhou}, Yihao and {Pacucci}, Fabio and {Ni}, Yueying and {Chen}, Nianyi and {Bird}, Simeon}, title = {{The Properties of Little Red Dot Galaxies in the ASTRID Simulation}}, journal = {The Open Journal of Astrophysics}, year = {2026}, month = jan, volume = {9}, pages = {55493}, doi = {10.33232/001c.155493}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026OJAp....955493L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, dust-reddened, early universe, simulation}, eprint = {2505.20439}, archiveprefix = {arXiv}, primaryclass = {astro-ph.CO}, month_numeric = {1} }

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Bridging Quasars and Little Red Dots: Insights into Broad-line Active Galactic Nuclei at z = 5─8 from the First JWST COSMOS-3D Dataset

Xiaojing Lin, Xiaohui Fan, Feige Wang, and 31 more authors

The Astrophysical Journal, Jan 2026

Abs DOI ADS arXiv

We report the discovery of 13 broad-line active galactic nuclei (AGNs) at z = 5─8 from the first 10% of JWST Cycle 3 Treasury Program COSMOS-3D. These AGNs are identified by their broad H\ensuremathα or H\ensuremathβ emission lines through NIRCam grism slitless spectroscopy. One object at z = 7.646 with broad H\ensuremathβ emission has an F444W magnitude of 23.6 mag, making it one of the brightest z > 7.5 broad-line AGNs yet known. Among the 13 AGNs, 10 objects exhibit reddened optical continua with slopes \ensuremathβ_opt > 0. The remaining three resemble UV-luminous quasars at similar redshift but with \ensuremathβ_opt less blue than those of typical unobscured quasars. We also obtain MIRI photometry (7.7─18 \ensuremathμm) for two AGNs and place strong constraints on their rest-frame near-IR spectral energy distribution. We find no significant variability in the rest-frame UV by comparing the COSMOS-3D and COSMOS-Web F115W images taken apart by 60 days in the rest-frame. We compute the H\ensuremathα luminosity function (LF) at z ≍ 5─6 and find potential redshift evolution compared to z ≍ 4─5. We also derive the H\ensuremathβ LF at z \ensuremath∼ 8 by combining our sample with those from the literature. The broad H\ensuremathβ emitters in this work suggest a number density 2 orders of magnitude higher than that predicted by the quasar LF based on rest-frame UV-selected samples. As a preview, our work showcases the ability of the COSMOS-3D grism survey to provide a complete view of the properties, growth, and evolution of bright broad-line AGNs at z > 5.

@article{2026ApJ...996...93L, author = {{Lin}, Xiaojing and {Fan}, Xiaohui and {Wang}, Feige and {Sun}, Fengwu and {Champagne}, Jaclyn B. and {Egami}, Eiichi and {Kakiichi}, Koki and {Lyu}, Jianwei and {Tee}, Wei Leong and {Yang}, Jinyi and {Bian}, Fuyan and {Bosman}, Sarah E. I. and {Cai}, Zheng and {Casey}, Caitlin M. and {Decarli}, Roberto and {Faisst}, Andreas L. and {Finkelstein}, Steven L. and {Fujimoto}, Seiji and {Harish}, Santosh and {Ilbert}, Olivier and {Inoue}, Akio K. and {Jin}, Xiangyu and {Kartaltepe}, Jeyhan S. and {Kocevski}, Dale D. and {Li}, Mingyu and {Liu}, Weizhe and {Liu}, Yichen and {Schindler}, Jan-Torge and {Shuntov}, Marko and {Tanaka}, Takumi S. and {Vestergaard}, Marianne and {Wu}, Yunjing and {Zhang}, Haowen and {Zhang}, Zijian}, title = {{Bridging Quasars and Little Red Dots: Insights into Broad-line Active Galactic Nuclei at z = 5─8 from the First JWST COSMOS-3D Dataset}}, journal = {\apj}, keywords = {Active galactic nuclei, Supermassive black holes, High-redshift galaxies, 16, 1663, 734}, year = {2026}, month = jan, volume = {996}, number = {1}, eid = {93}, pages = {93}, doi = {10.3847/1538-4357/ae1b9b}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...996...93L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, sed, spectroscopy}, eprint = {2504.08039}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Mysterious ’little red dots’ could be black holes in disguise

Rodrigo Nemmen

Nature, Jan 2026

Abs DOI ADS

Analysis indicates that the light from ’little red dots’ is generated by young supermassive black holes obscured by dense clouds of gas.

@article{2026Natur.649..557N, author = {{Nemmen}, Rodrigo}, title = {{Mysterious 'little red dots' could be black holes in disguise}}, journal = {\nat}, keywords = {Astronomy and astrophysics}, year = {2026}, month = jan, volume = {649}, number = {8097}, pages = {557-558}, doi = {10.1038/d41586-025-04089-y}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026Natur.649..557N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, early universe, sed, spectroscopy}, month_numeric = {1} }

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The Little Red Dots Are Direct Collapse Black Holes

Fabio Pacucci, Andrea Ferrara, and Dale D. Kocevski

arXiv e-prints, Jan 2026

Abs ADS arXiv

The discovery by JWST of a substantial population of compact “Little Red Dots” (LRDs) presents a major puzzle: their observed spectra defy standard astrophysical interpretations. Here, we show that LRD spectra are naturally reproduced by emission from an accreting Direct Collapse Black Hole (DCBH). Using radiation- hydrodynamic simulations, we follow the growth of the DCBH seed via a dense, compressionally heated, collisionally ionized accretion flow. The model self-consistently reproduces the screen responsible for the observed Balmer absorption, while allowing UV/optical emission to partially escape, along with reprocessed infrared radiation. Crucially, this structure is not a blackbody and requires no stellar contribution: the UV continuum originates entirely from reprocessed DCBH radiation, attenuated only by a small amount of dust with an extinction curve consistent with high-redshift galaxies. This single framework simultaneously explains the key observational puzzles of LRDs: (a) weak X-ray emission, (b) metal and high-ionization lines alongside absent star-formation features, (c) overmassive black holes, (d) compact morphology, (e) abundance and redshift evolution – linking them directly to pristine atomic-cooling halos, (f) long-lived (>100 Myr), slowly variable phases driven by radiation pressure. Our findings indicate that JWST is witnessing the widespread formation of heavy black hole seeds in the early Universe.

@article{2026arXiv260114368P, author = {{Pacucci}, Fabio and {Ferrara}, Andrea and {Kocevski}, Dale D.}, title = {{The Little Red Dots Are Direct Collapse Black Holes}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2026}, month = jan, eid = {arXiv:2601.14368}, pages = {arXiv:2601.14368}, archiveprefix = {arXiv}, eprint = {2601.14368}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260114368P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, month_numeric = {1} }

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Little red dots as young supermassive black holes in dense ionized cocoons

V. Rusakov, D. Watson, G. P. Nikopoulos, and 14 more authors

Nature, Jan 2026

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has uncovered many compact galaxies at high redshift with broad hydrogen and helium lines, including the enigmatic population of little red dots (LRDs)^1,2. The nature of these galaxies is debated and is attributed to supermassive black holes (SMBHs)^3,4 or intense star formation^5. They exhibit unusual properties for SMBHs, such as black holes that are overmassive for their host galaxies^4 and extremely weak X-ray^6, 7, 8, 9─10 and radio^6,11, 12─13 emission. Here we show that in most objects studied with the highest-quality JWST spectra, the lines are broadened by electron scattering with a narrow intrinsic core. The data require very high electron column densities and compact sizes (light days), which, when coupled with their high luminosities, can be explained only by SMBH accretion. The narrow intrinsic line cores imply black hole masses of 10^5\ensuremath-7M_\ensuremath⊙, two orders of magnitude lower than previous estimates. These are the lowest mass black holes known at high redshift, to our knowledge, and suggest a population of young SMBHs. They are enshrouded in a dense cocoon of ionized gas producing broad lines from which they are accreting close to the Eddington limit, with very mild neutral outflows. Reprocessed nebular emission from this cocoon dominates the optical spectrum, explaining most LRD spectral characteristics, including the weak radio and X-ray emission^14,15.

@article{2026Natur.649..574R, author = {{Rusakov}, V. and {Watson}, D. and {Nikopoulos}, G. P. and {Brammer}, G. and {Gottumukkala}, R. and {Harvey}, T. and {Heintz}, K. E. and {Damgaard}, R. and {Sim}, S. A. and {Sneppen}, A. and {Vijayan}, A. P. and {Adams}, N. and {Austin}, D. and {Conselice}, C. J. and {Goolsby}, C. M. and {Toft}, S. and {Witstok}, J.}, title = {{Little red dots as young supermassive black holes in dense ionized cocoons}}, journal = {\nat}, keywords = {Physical Sciences, Astronomical and Space Sciences}, year = {2026}, month = jan, volume = {649}, number = {8097}, pages = {574-579}, doi = {10.1038/s41586-025-09900-4}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026Natur.649..574R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, eprint = {2503.16595}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Do Little Red Dots Vary?

Amy Secunda, Rachel S. Somerville, Yan-Fei Jiang, and 3 more authors

The Astrophysical Journal, Jan 2026

Abs DOI ADS arXiv

Little red dots (LRDs), high-redshift, compact, red objects with V-shaped spectra, are one of the most exciting and perplexing discoveries made by the James Webb Space Telescope (JWST). While the simplest explanation for LRDs is that they are high-redshift active galactic nuclei (AGN), due to their compactness and frequent association with broad-line emission, the lack of corresponding X-ray emission and observed variability casts doubt on this picture. Here, we simulate LRD light curves using both traditional models for sub-Eddington AGN variability derived empirically from lower-redshift AGN observations and moderately super-Eddington AGN disk models from radiation magnetohydrodynamic simulations to examine the reason for the lack of variability. We find that even though most LRDs have only been observed two to four times in a given wave band, we should still be detecting significantly more variability if traditional sub-Eddington AGN variability models can be applied to LRDs. Instead, our super-Eddington model light curves are consistent with the lack of observed LRD variability. In addition, the ongoing high-cadence NEXUS campaign will detect changes in magnitude \ensuremath∆m > 1 for traditional sub-Eddington models, but will only observe significant continuum variability for the lowest-mass LRDs for our super- Eddington AGN models. Even if LRDs lack continuum variability, we find that the ongoing spectroscopic JWST campaign TWINKLE should observe broad emission line variability as long as soft X-ray irradiation manages to reach the broad-line region from the inner disk. Our models show that super-Eddington accretion can easily explain the lack of continuum variability in LRDs.

@article{2026ApJ...996....6S, author = {{Secunda}, Amy and {Somerville}, Rachel S. and {Jiang}, Yan-Fei and {Greene}, Jenny E. and {Furtak}, Lukas J. and {Zitrin}, Adi}, title = {{Do Little Red Dots Vary?}}, journal = {\apj}, keywords = {Active galactic nuclei, High energy astrophysics, Active galaxies, James Webb Space Telescope, Radiative magnetohydrodynamics, 16, 739, 17, 2291, 2009}, year = {2026}, month = jan, volume = {996}, number = {1}, eid = {6}, pages = {6}, doi = {10.3847/1538-4357/ae1f08}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026ApJ...996....6S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, simulation, theory, variability}, eprint = {2509.03571}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Inside the cocoon: a comprehensive explanation of the spectra of Little Red Dots

A. Sneppen, D. Watson, J. H. Matthews, and 10 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

JWST has revealed a population of compact galaxies in the early Universe with broad emission lines and strong Balmer breaks; among them the so-called “little red dots” (LRDs). Their nature remains uncertain with hypotheses including exotic phenomena. We assemble a sample of LRD-like objects at z>3 and use self- consistent radiative-transfer calculations to show that a supermassive black hole accreting from a dense gas cocoon accurately reproduces the detailed spectra. We show that the cocoons must be non-spherical, with comparable amounts of inflowing and outflowing material. And we predict correlations between Balmer break strength, Balmer line-absorption and scattering line width, which we confirm in our observed sample. We reproduce all LRD-like properties without requiring star-like atmospheres and we determine the typical black hole in our sample to be of order a million solar masses, with ionized cocoon masses of tens of solar masses potentially supplied from a much larger cold-gas reservoir.

@article{2026arXiv260118864S, author = {{Sneppen}, A. and {Watson}, D. and {Matthews}, J. H. and {Nikopoulos}, G. and {Allen}, N. and {Brammer}, G. and {Damgaard}, R. and {Heintz}, K. E. and {Knigge}, C. and {Long}, K. S. and {Rusakov}, V. and {Sim}, S. A. and {Witstok}, J.}, title = {{Inside the cocoon: a comprehensive explanation of the spectra of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2026}, month = jan, eid = {arXiv:2601.18864}, pages = {arXiv:2601.18864}, archiveprefix = {arXiv}, eprint = {2601.18864}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260118864S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, early universe, simulation, spectroscopy}, month_numeric = {1} }

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A weak Ly\ensuremathα halo for an extremely bright little red dot: Indications of enshrouded supermassive black hole growth

Alberto Torralba, Jorryt Matthee, Gabriele Pezzulli, and 13 more authors

Astronomy & Astrophysics, Jan 2026

Abs DOI ADS arXiv

The abundant population of little red dots (LRDs), compact objects with red UV to optical colors and broad Balmer lines at high redshift, is revealing new insights into the properties of early active galactic nuclei (AGN). Perhaps the most surprising features of this population are the presence of Balmer absorption and ubiquitous strong Balmer breaks. Recent models link these features to an active supermassive black hole (SMBH) cocooned in very dense gas (N_H \ensuremath∼ 10^24 cm^\ensuremath-2). We present a stringent test of such models using VLT/MUSE observations of A2744-45924, the most luminous LRD known to date (L_H\ensuremathα ≍ 10^44 erg s^\ensuremath-1), located behind the Abell-2744 lensing cluster at z = 4.464 (\ensuremathμ = 1.8). We detect a moderately extended Ly\ensuremathα nebula (h ≍ 5.7 pkpc), spatially offset from the point-like H\ensuremathα seen by JWST by ≍1.6 pkpc. The Ly\ensuremathα emission is narrow (FWHM = 270 \ensuremath\pm 15 km s^\ensuremath-1), and faint (Ly\ensuremathα = 0.07H\ensuremathα) compared to Ly\ensuremathα nebulae typically observed around quasars of similar luminosity. We detect compact N IV]\ensuremathλ1486 emission, spatially aligned with H\ensuremathα, and a spatial shift in the far-UV continuum matching the Ly\ensuremathα offset. We discuss that H\ensuremathα and Ly\ensuremathα have distinct physical origins: H\ensuremathα originates from the AGN, while Ly\ensuremathα is powered by star formation. In the environment of A2744-45924, we identified four extended Ly\ensuremathα halos (\ensuremath∆z < 0.02, \ensuremath∆r < 100 pkpc). Their Ly\ensuremathα luminosities match the expectations based on H\ensuremathα emission, and show no evidence for radiation from A2744-45924 affecting its surroundings. The lack of strong, compact, and broad Ly\ensuremathα and the absence of a luminous extended halo, suggest that the UV AGN light is obscured by dense gas cloaking the SMBH with a covering factor close to unity.

@article{2026A&A...705A.147T, author = {{Torralba}, Alberto and {Matthee}, Jorryt and {Pezzulli}, Gabriele and {Urrutia}, Tanya and {Gronke}, Max and {Mascia}, Sara and {D'Eugenio}, Francesco and {Di Cesare}, Claudia and {Eilers}, Anna-Christina and {Greene}, Jenny E. and {Iani}, Edoardo and {Ishikawa}, Yuzo and {Mackenzie}, Ruari and {Naidu}, Rohan P. and {Navarrete}, Benjam{\'\i}n and {Kotiwale}, Gauri}, title = {{A weak Ly{\ensuremath{\alpha}} halo for an extremely bright little red dot: Indications of enshrouded supermassive black hole growth}}, journal = {\aap}, keywords = {galaxies: active, galaxies: halos, galaxies: high-redshift}, year = {2026}, month = jan, volume = {705}, eid = {A147}, pages = {A147}, doi = {10.1051/0004-6361/202555596}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026A\&A...705A.147T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, spectroscopy}, eprint = {2505.09542}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {1} }

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Distant ’little red dot’ galaxies may contain baby black holes

Alex Wilkins

New Scientist, Jan 2026

DOI ADS

@article{2026NewSc.269S..13W, author = {{Wilkins}, Alex}, title = {{Distant 'little red dot' galaxies may contain baby black holes}}, journal = {New Scientist}, year = {2026}, month = jan, volume = {269}, number = {3579}, pages = {13-13}, doi = {10.1016/S0262-4079(26)00117-X}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026NewSc.269S..13W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, heavy seed, non-agn, theory}, month_numeric = {1} }

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JADES: A Prominent Galaxy Overdensity Candidate within the First 500 Myr

Zihao Wu, Daniel J. Eisenstein, Benjamin D. Johnson, and 20 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

We report a galaxy overdensity candidate at z≈10.5 in the JWST Advanced Deep Extragalactic Survey (JADES). This overdensity contains 18 galaxies with consistent photometric redshifts and robust F115W dropouts within 8 comoving Mpc in projection. The galaxy number density is four times higher than the field expectation, accounting for one-third of comparably bright galaxies and nearly 50% of the total star formation rate at 10<z_\mathrmphot<12 in the GOODS-S field. Two compact members of the overdensity show potential Balmer breaks suggestive of evolved stellar populations or little red dots (LRDs). One-third of galaxies have close companions or substructures within 1 kpc at consistent photometric redshifts, implying more frequent interactions in an overdense environment. Most galaxies have stellar masses of 0.6-3\times10^8 M_⊙, half-light radii of \sim200 pc, and star formation rates of \sim5 M_⊙\mathrmyr^-1, with no significant deviation from typical high-redshift scaling relations. We find tentative evidence for a spatially varying Lyα transmission inferred photometrically, consistent with an emerging ionized bubble. This overdensity provides a rare opportunity for probing the environmental impact on galaxy evolution and the onset of cosmic reionization within the first 500 Myr.

@article{2026arXiv260115960W, author = {{Wu}, Zihao and {Eisenstein}, Daniel J. and {Johnson}, Benjamin D. and {Hainline}, Kevin and {Baker}, William M. and {Bunker}, Andrew J. and {Cameron}, Alex J. and {Curtis-Lake}, Emma and {Danhaive}, A. Lola and {Hausen}, Ryan and {Helton}, Jakob M. and {Ji}, Zhiyuan and {Looser}, Tobias J. and {Maiolino}, Roberto and {Mengistu}, Petra and {Rinaldi}, Pierluigi and {Robertson}, Brant E. and {Sun}, Fengwu and {Tacchella}, Sandro and {Trussler}, James A. A. and {Williams}, Christina C. and {Willmer}, Christopher N. A. and {Witstok}, Joris}, title = {{JADES: A Prominent Galaxy Overdensity Candidate within the First 500 Myr}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jan, eid = {arXiv:2601.15960}, pages = {arXiv:2601.15960}, archiveprefix = {arXiv}, eprint = {2601.15960}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260115960W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {clustering, early universe, jwst, photometry, starburst}, month_numeric = {1} }

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VENUS: Two Faint Little Red Dots Separated by \sim70\,\mathrmpc Hidden in a Single Lensed Galaxy at z\sim7

Hiroto Yanagisawa, Masami Ouchi, Miriam Golubchik, and 47 more authors

arXiv e-prints, Jan 2026

Abs ADS arXiv

We report the identification of a pair of faint little red dots (LRDs), dubbed Red Eyes, in a strongly-lensed galaxy at z\sim7 behind the PLCKG004.5-10.5 cluster, identified from the JWST Treasury program VENUS. Red Eyes are spatially resolved on the image plane with distinct colors, while the critical curve lies far north of Red Eyes, clearly requiring two different LRDs rather than a single LRD. Red Eyes is an extremely close pair of LRDs separated by \sim70\,\mathrmpc in the source plane with a magnification of μ\sim20, which consistently explains another counter-image detected to the north-west. Red Eyes is hosted in a typical star-forming galaxy with M_\mathrmUV,int∼-19, but its own UV emission is very faint (M_\mathrmUV,int rsim -16). Moreover, Red Eyes does not reside at the galaxy center but lies at an offset position of approximately one effective radius R_\mathrme away from the galaxy center. If observed without lensing, Red Eyes would appear as a typical star-forming galaxy at z∼7 with M_\mathrmUV∼-19, showing no apparent LRD signatures in either morphology or SED. These results suggest that multiple off-center LRDs, similar to Red Eyes, may be commonly hidden in a typical high-z star-forming galaxy. In this case, various plausible scenarios may emerge, one of which is that intermediate-mass black holes (IMBHs) with M_\mathrmBH\sim10^4\text–6 M_⊙may form in star clusters on a stellar disk and contribute to the growth of the central supermassive black hole via mergers, with some IMBHs detectable as luminous LRDs in a sufficiently active and massive phase.

@article{2026arXiv260106015Y, author = {{Yanagisawa}, Hiroto and {Ouchi}, Masami and {Golubchik}, Miriam and {Oguri}, Masamune and {Fujimoto}, Seiji and {Kokorev}, Vasily and {Brammer}, Gabriel and {Sun}, Fengwu and {Nakane}, Minami and {Harikane}, Yuichi and {Umeda}, Hiroya and {Akins}, Hollis B. and {Atek}, Hakim and {Bauer}, Franz E. and {Brada{\v{c}}}, Maru{\v{s}}a and {Chisholm}, John and {Coe}, Dan and {Diego}, Jose M. and {Ferguson}, Henry C. and {Finkelstein}, Steven L. and {Furtak}, Lukas J. and {Inayoshi}, Kohei and {Koekemoer}, Anton M. and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Ono}, Yoshiaki and {Pan}, Richard and {Richard}, Johan and {Robbins}, Luke and {Willott}, Chris and {Zitrin}, Adi and {Amor{\'\i}n}, Ricardo O. and {Bradley}, Larry D. and {Bromm}, Volker and {Conselice}, Christopher J. and {Dayal}, Pratika and {Kartaltepe}, Jeyhan S. and {Lopes}, Paulo A. A. and {Lucas}, Ray A. and {Magdis}, Georgios E. and {Martis}, Nicholas S. and {Papovich}, Casey and {Schaerer}, Daniel and {Valentino}, Francesco and {Vanzella}, Eros and {Allingham}, Joseph F. V. and {Grogin}, Norman A. and {Gonz{\'a}lez-Otero}, Mauro and {Ricotti}, Massimo and {Windhorst}, Rogier A.}, title = {{VENUS: Two Faint Little Red Dots Separated by $\sim70\,\mathrm{pc}$ Hidden in a Single Lensed Galaxy at $z\sim7$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2026}, month = jan, eid = {arXiv:2601.06015}, pages = {arXiv:2601.06015}, archiveprefix = {arXiv}, eprint = {2601.06015}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260106015Y}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, morphology, non-agn}, month_numeric = {1} }

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2025

(Re)solving the complex multi-scale morphology and V-shaped SED of a newly discovered strongly-lensed Little Red Dot in Abell 383

Josephine F. W. Baggen, Pieter van Dokkum, Ivo Labbé, and 1 more author

arXiv e-prints, Dec 2025

Abs ADS arXiv

We present a luminous Little Red Dot (LRD) at z=6.027, doubly imaged by the galaxy cluster Abell 383 and observed with JWST/NIRCam. The source shows the characteristic “V-shaped” SED and pronounced Balmer break that define the LRD population. Owing to its large magnifications, μ\sim11 for image S1 and μ\sim7 for S2, the system is exceptionally bright and highly stretched, providing a rare, spatially resolved view of an LRD. The images reveal a complex morphology with a compact red dot, a spatially offset blue dot, and faint emission bridging and surrounding the two. After correcting for lensing, we find that both dots are extremely small but resolved, with rest-frame UV sizes of ∼20 pc (red) and \sim60 pc (blue). These compact dots are embedded in a more extended, line-dominated cloud traced most clearly in F356W ([OIII]+Hβ), which reaches scales of order \sim1 kpc. SED decomposition shows that the blue component has a flat UV continuum consistent with a young stellar population, whereas the red component has a steep red SED that can be interpreted as either an evolved stellar population with high stellar mass (\log M_⋆/M_⊙>10) or a reddened AGN. If this object is representative of the LRD population, our results imply that the V-shaped SEDs of LRDs do not arise from individual compact sources but instead from the superposition of two physically distinct components. Separated by only \sim300 pc in the source plane, these components would blend into a single compact source in unlensed observations with the canonical LRD colors. This system therefore provides a rare opportunity to resolve the internal structure of an LRD and to gain direct insight into the physical nature of this population.

@article{2025arXiv251203239B, author = {{Baggen}, Josephine F. W. and {van Dokkum}, Pieter and {Labb{\'e}}, Ivo and {Brammer}, Gabriel}, title = {{(Re)solving the complex multi-scale morphology and V-shaped SED of a newly discovered strongly-lensed Little Red Dot in Abell 383}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.03239}, pages = {arXiv:2512.03239}, archiveprefix = {arXiv}, eprint = {2512.03239}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251203239B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, morphology, non-agn, sed, starburst}, month_numeric = {12} }

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Dust Budget Crisis in Little Red Dots

Kejian Chen, Zhengrong Li, Kohei Inayoshi, and 1 more author

The Astrophysical Journal Letters, Dec 2025

Abs DOI ADS arXiv

Little red dots (LRDs), a population of active galactic nuclei (AGNs) recently identified by JWST, are characterized by their compact morphology and red optical continuum emission, which is often interpreted as evidence for significant dust extinction of A_V \ensuremath≳ 3 mag. However, the dust-reddened AGN scenario is increasingly challenged by their faint near-to- far-infrared emission and a potential “dust budget crisis” in cases when the host galaxy is either undetectably low-mass or absent. In this study, we reevaluate the dust extinction level in LRDs by modeling the UV-to-infrared spectra for various extinction laws and a broad range of dusty distribution parameters. Comparing the predicted infrared fluxes with observational data from JWST MIRI, Herschel, and the Atacama Large Millimeter/submillimeter Array, our analysis finds that the visual extinction is tightly and consistently constrained to A_V \ensuremath≲ 1.0─1.5 mag for A2744─45924, RUBIES-BLAGN-1, and stacked spectral energy distributions from a large sample of LRDs under the SMC extinction law, with slightly weaker constraints for those with gray extinction in the UV range. The revised A_V values yield radiative efficiencies of \ensuremath∼10% for the LRD population, easing the tension with the Sołtan argument for the bulk AGN population at lower redshifts. Moreover, this moderate extinction (or dust- free) scenario, with reprocessed emission spectra testable by future far-infrared observatories, provides a paradigm shift in understanding the natures, environments, and evolutionary pathways of massive black holes in the early Universe.

@article{2025ApJ...994L..42C, author = {{Chen}, Kejian and {Li}, Zhengrong and {Inayoshi}, Kohei and {Ho}, Luis C.}, title = {{Dust Budget Crisis in Little Red Dots}}, journal = {\apjl}, keywords = {Galaxy formation, High-redshift galaxies, Quasars, Supermassive black holes, Interstellar medium, Astrophysical dust processes, 595, 734, 1319, 1663, 847, 99}, year = {2025}, month = dec, volume = {994}, number = {2}, eid = {L42}, pages = {L42}, doi = {10.3847/2041-8213/ae1955}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994L..42C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, early universe, jwst, multi-wavelength, sed}, eprint = {2505.22600}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {12} }

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Active galactic nuclei-heated dust revealed in “little red dots”

I. Delvecchio, E. Daddi, B. Magnelli, and 11 more authors

Astronomy & Astrophysics, Dec 2025

Abs DOI ADS arXiv

Little red dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this work, we performed a comprehensive stacking analysis of NIRCam, MIRI, and ALMA images of a large and homogeneously selected sample of LRDs from multiple JWST Legacy fields. We report clear evidence of hot-dust emission in the median stacked spectral energy distribution (SED) that features a rising near-infrared continuum up to rest-frame \ensuremathλ_rest \ensuremath∼ 3 \ensuremathμm, which is best explained by a standard dusty active galactic nucleus (AGN) structure. Although LRDs are likely to be a heterogeneous population, our findings suggest that most (\ensuremath≳50%) LRDs show AGN-heated dust emission, regardless of whether the optical and ultraviolet (UV) continua are stellar or AGN-dominated. In either case, the best-fit dusty-AGN SED, combined with the lack of X-ray detection in the deep Chandra stacks, suggests that Compton-thick (N_H > 3 \texttimes 10^24 cm^\ensuremath-2) gas obscuration is common, and likely confined within the dust sublimation radius (R_sub \ensuremath∼ 0.1 pc). Therefore, we argue that AGN-heated dust does not directly obscure either the optical-UV continuum or the broad-line region emission, in order to explain the observed blue UV slopes and prominent Balmer features. While a gas-dust displacement is in line with several models, the formation scenario (in-situ or ex- situ) of this pre-enriched hot dust remains unclear.

@article{2025A&A...704A.313D, author = {{Delvecchio}, I. and {Daddi}, E. and {Magnelli}, B. and {Elbaz}, D. and {Giavalisco}, M. and {Traina}, A. and {Lanzuisi}, G. and {Akins}, H. B. and {Belli}, S. and {Casey}, C. M. and {Gentile}, F. and {Gruppioni}, C. and {Pozzi}, F. and {Zamorani}, G.}, title = {{Active galactic nuclei-heated dust revealed in ``little red dots''}}, journal = {\aap}, keywords = {galaxies: active, galaxies: evolution, galaxies: high-redshift, quasars: general, quasars: supermassive black holes}, year = {2025}, month = dec, volume = {704}, eid = {A313}, pages = {A313}, doi = {10.1051/0004-6361/202557164}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...704A.313D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, sed, x-ray}, eprint = {2509.07100}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {12} }

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On the Fate of Little Red Dots

Andrés Escala, Lucas Zimmermann, Sebastián Valdebenito, and 3 more authors

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

We study the stability and possible fates of little red dots (LRDs) under the stellar-only interpretation of their observational features. This is performed by a combination of analyzing the relevant timescales in their stellar dynamics and also the application of recent numerical results on the evolution of the densest stellar systems. We find that these objects typically have t_age \ensuremath∼ t_coll < t_relax and are therefore in an unexplored regime never observed before for a stellar system and are potentially highly unstable to runaway collisions. We study different scenarios for the evolution of LRDs and conclude that in a fair fraction of those systems, the formation of a massive black hole (MBH) by runaway stellar collisions seems unavoidable, in all the possibilities studied within the stellar-only interpretation. This evolutionary path would naturally explain many of the problematic characteristics of Little Red Dots, including that these objects are probably transient in the history of the Universe, that most of them would not emit X-rays since they would not yet have become MBHs, and once they do, they would constitute a significant portion of the mass of LRDs. We conclude that LRDs are the most favorable known places to find a recently formed MBH seed or, in the process of formation, that are most probably formed directly within the supermassive range.

@article{2025ApJ...995...44E, author = {{Escala}, Andr{\'e}s and {Zimmermann}, Lucas and {Valdebenito}, Sebasti{\'a}n and {Vergara}, Marcelo C. and {Schleicher}, Dominik R. G. and {Liempi}, Mat{\'\i}as}, title = {{On the Fate of Little Red Dots}}, journal = {\apj}, keywords = {Astrophysical black holes, 98, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2025}, month = dec, volume = {995}, number = {1}, eid = {44}, pages = {44}, doi = {10.3847/1538-4357/ae200e}, archiveprefix = {arXiv}, eprint = {2509.20453}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...995...44E}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, simulation, starburst, theory, x-ray}, month_numeric = {12} }

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Radio Constraints Disfavor Little Red Dots as Scaled-down Super-Eddington Quasars

Carl Audric Guia and Fabio Pacucci

Research Notes of the American Astronomical Society, Dec 2025

Abs DOI ADS

The Little Red Dots (LRDs) exhibit signatures of active galactic nucleus yet remain undetected in radio and X-ray observations, including deep stacking analyses. These properties have motivated models in which LRDs host supermassive black holes accreting at super- Eddington rates. We test whether LRDs could be scaled-down analogs of super-Eddington quasars like RACS J0320-35 at z = 6.13, whose spectral energy distribution is well reproduced by super-Eddington models. Using observed rest-frame UV luminosities of LRDs, we construct radio predictions for scaled- down versions of RACS J0320-35, then compare them with observational upper limits on radio emission. Most predictions at z < 5 exceed the radio stacking limits of \ensuremath∼10 \ensuremathμJy for LRDs, except for faint LRDs with UV luminosity \ensuremath∼10^43 erg s^\ensuremath-1. However, our predictions remain well below radio detection limits for individual sources in the VLA Sky Survey. We conclude that LRDs are unlikely to be scaled-down versions of super-Eddington quasars, although deeper radio surveys like DSA-2000 will improve constraints.

@article{2025RNAAS...9..355G, author = {{Guia}, Carl Audric and {Pacucci}, Fabio}, title = {{Radio Constraints Disfavor Little Red Dots as Scaled-down Super-Eddington Quasars}}, journal = {Research Notes of the American Astronomical Society}, keywords = {Active galactic nuclei, Early universe, Quasars, Radio sources, Supermassive black holes, 16, 435, 1319, 1358, 1663}, year = {2025}, month = dec, volume = {9}, number = {12}, eid = {355}, pages = {355}, doi = {10.3847/2515-5172/ae3179}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025RNAAS...9..355G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {non-agn, radio, sed, theory, x-ray}, month_numeric = {12} }

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A Critical Evaluation of the Physical Nature of the Little Red Dots

Kohei Inayoshi and Luis C. Ho

arXiv e-prints, Dec 2025

Abs ADS arXiv

Little Red Dots (LRDs) are a newly identified class of active galactic nuclei (AGNs) uncovered by JWST deep surveys. Their enigmatic properties challenge the canonical AGN paradigm and have stimulated ideas on early massive black hole (BH) formation. In this review, we summarize how early BHs shape the characteristic features of LRDs, how their nuclear environments differ from those of normal AGNs, and how future observations can distinguish between competing scenarios. Our main conclusions are as follows: (1) LRDs show broad-line emission consistent with mass accretion onto BHs with M_\rm BH≃10^6-7~M_⊙, suggesting that AGN activity is a plausible origin of their dominant red optical emission. (2) Stellar components can reproduce the continuum energetics through dusty star formation. However, the required stellar mass would be too large to remain consistent with other LRD properties. Therefore, a purely stellar origin is unlikely to be the dominant power source, although star formation may still contribute to the UV emission. (3) The coexistence of broad-line emission with Balmer absorption and break features on LRD spectra, neither of which can be explained by stellar populations, suggests that nuclear BHs are enshrouded by dense gas with a high covering fraction. (4) Gas-enshrouded AGNs can produce red optical spectra without requiring dust reddening through a combination of gas attenuation and thermal self-emission with an effective temperature of T_\rm eff≃5000~\rm K, which also accounts for the flat infrared continuum. (5) From the spectral features and redshift evolution, LRDs are likely a transient phase in early BH growth, possibly the first accretion episodes of newborn BHs. (6) Testing models for LRD spectra and origins through time variability, ionizing sources, post-LRD objects, and low-redshift analogs is particularly promising.

@article{2025arXiv251203130I, author = {{Inayoshi}, Kohei and {Ho}, Luis C.}, title = {{A Critical Evaluation of the Physical Nature of the Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.03130}, pages = {arXiv:2512.03130}, archiveprefix = {arXiv}, eprint = {2512.03130}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251203130I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, theory}, month_numeric = {12} }

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BlackTHUNDER ─ A non-stellar Balmer break in a black hole-dominated little red dot at z = 7.04

Xihan Ji, Roberto Maiolino, Hannah Übler, and 34 more authors

Monthly Notices of the Royal Astronomical Society, Dec 2025

Abs DOI ADS arXiv

Recent observations from James Webb Space Telescope (JWST) have revealed an abundant population of active galactic nuclei (AGNs) and the so-called ’Little Red Dots’ (LRDs) at , many of which are characterized by V-shaped UV-to-optical continua with turnovers around the Balmer limit. The physical nature of these LRDs is unclear, and it remains debated whether the peculiar spectral shape originates from AGN, compact galaxies, or both. We present the analysis of new NIRSpec-IFU data from the BlackTHUNDER JWST Large Programme and archival NIRSpec-MSA data of a lensed LRD at . The spectra confirm the presence of a smooth Balmer break and a broad H tracing the Broad Line Region (BLR) of an AGN. The small velocity dispersion of the H narrow component indicates a small dynamical mass of the host galaxy of , which implies that the stellar population cannot contribute more than 10 per cent to the optical continuum. We show that the Balmer break can be well described by an AGN continuum absorbed by very dense () and nearly dust-free gas along our line of sight (possibly gas in the BLR or its surrounding). The same gas is expected to produce H absorption, at a level consistent with a tentative detection () in the high-resolution spectrum. Such a non-stellar origin of the Balmer break may apply to other LRDs, and would alleviate the issue of extremely high stellar mass surface densities inferred in the case of a stellar interpretation of the Balmer break. We note that this is a rare case of a black hole that is overmassive relative to both the host galaxy stellar and dynamical masses. We finally report indications of variability and the first attempt of AGN reverberation mapping at such an early epoch.

@article{2025MNRAS.544.3900J, author = {{Ji}, Xihan and {Maiolino}, Roberto and {{\"U}bler}, Hannah and {Scholtz}, Jan and {D'Eugenio}, Francesco and {Sun}, Fengwu and {Perna}, Michele and {Turner}, Hannah and {Carniani}, Stefano and {Arribas}, Santiago and {Bennett}, Jake S. and {Bunker}, Andrew and {Charlot}, St{\'e}phane and {Cresci}, Giovanni and {Curti}, Mirko and {Egami}, Eiichi and {Fabian}, Andy and {Inayoshi}, Kohei and {Isobe}, Yuki and {Jones}, Gareth and {Juod{\v{z}}balis}, Ignas and {Kumari}, Nimisha and {Lyu}, Jianwei and {Mazzolari}, Giovanni and {Parlanti}, Eleonora and {Robertson}, Brant and {Rodr{\'\i}guez Del Pino}, Bruno and {Schneider}, Raffaella and {Sijacki}, Debora and {Tacchella}, Sandro and {Trinca}, Alessandro and {Valiante}, Rosa and {Venturi}, Giacomo and {Volonteri}, Marta and {Willott}, Chris and {Witten}, Callum and {Witstok}, Joris}, title = {{BlackTHUNDER ─ A non-stellar Balmer break in a black hole-dominated little red dot at z = 7.04}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: high-redshift, Astrophysics of Galaxies}, year = {2025}, month = dec, volume = {544}, number = {4}, pages = {3900-3935}, doi = {10.1093/mnras/staf1867}, archiveprefix = {arXiv}, eprint = {2501.13082}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.544.3900J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, spectroscopy, variability}, month_numeric = {12} }

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Black hole envelopes in Little Red Dots

Daisaburo Kido, Kunihito Ioka, Kenta Hotokezaka, and 2 more authors

Monthly Notices of the Royal Astronomical Society, Dec 2025

Abs DOI ADS arXiv

Recent observations by the James Webb Space Telescope have uncovered a population of compact, red object () known as Little Red Dots (LRDs). The presence of broad Balmer emission lines implies active galactic nuclei powered by supermassive black holes (BHs), while LRDs exhibit unusually weak X-ray and radio emission and low variability, suggesting super-Eddington accretion that obscures the central engine. We suggest that such an extreme accretion disc inevitably drives strong outflows, which would disrupt the LRDs themselves unless confined within the nuclear region ─ posing a general feedback problem for overmassive BHs. To resolve this, we propose that the BH is embedded in a massive, optically thick envelope that gravitationally confines the outflow, making any outflow a no- go. This envelope, powered by accretion on to the BH, radiates at nearly the Eddington limit, and is sustained by an infall of the interstellar medium at a rate on the order of \ensuremath∼1 . A photosphere emerges either within the envelope or in the infalling medium, with a characteristic temperature of 5000─, near the Hayashi limit. The resulting blackbody emission naturally explains the red optical continuum of the distinct V-shaped spectrum observed in most LRDs. Furthermore, the dynamical time-scale at the photosphere, \ensuremath∼0.01 pc, is consistent with the observed year-scale variabilities. The nuclear structure and spectral features of LRDs are shaped by this envelope, which not only regulates feedback but also acts as a gas reservoir that sustains rapid BH growth in the early universe.

@article{2025MNRAS.544.3407K, author = {{Kido}, Daisaburo and {Ioka}, Kunihito and {Hotokezaka}, Kenta and {Inayoshi}, Kohei and {Irwin}, Christopher M.}, title = {{Black hole envelopes in Little Red Dots}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: high-redshift, quasars: supermassive black holes}, year = {2025}, month = dec, volume = {544}, number = {4}, pages = {3407-3416}, doi = {10.1093/mnras/staf1898}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.544.3407K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, sed, theory}, eprint = {2505.06965}, archiveprefix = {arXiv}, primaryclass = {astro-ph.HE}, month_numeric = {12} }

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Highly-ionized gas in lensed z = 6.027 Little Red Dot seen through [OIII] 88μm with ALMA

Kirsten K. Knudsen, Johan Richard, Mathilde Jauzac, and 8 more authors

arXiv e-prints, Dec 2025

Abs ADS arXiv

Determining the physical properties of galaxies during the first billion years after the big bang is key to understanding both early galaxy evolution and how galaxies contributed to the epoch of reionization. We present deep ALMA observations of the redshifted [OIII] 88um line for the gravitationally lensed (μ= 11.4\pm1.9) galaxy A383-5.1 (z=6.027) that has previously been detected in [CII] 158um. Recent James Webb Space Telescope (JWST) imaging identified this sub-L* galaxy as a “Little Red Dot” (LRD). With a line luminosity of L_\rm [OIII] = (1.29\pm0.24)\times10^8 L_⊙(corrected for lensing magnification) A383-5.1 is one of the faintest galaxies with combined [CII] and [OIII] detections. The ALMA data reveal no dust continuum emission, consistent with previous observations. The high line luminosity ratio of [OIII]/[CII] ∼14\pm5 is consistent with A383-5.1 being low-metallicity and dust-poor. The non-detection of dust continuum in bands 6 and 8 is consistent with the high [OIII]/[CII] ratio and suggests a presence of a strong ultraviolet radiation field, which would be less affect by dust attenuation, implying that galaxies of this type could contribute significantly to the ionization of the intergalactic medium. The presence of strong ionizing field could provide an important piece of information for understanding the nature of LRDs and their role in cosmic reionization.

@article{2025arXiv251205097K, author = {{Knudsen}, Kirsten K. and {Richard}, Johan and {Jauzac}, Mathilde and {Bakx}, Tom J. L. C. and {Goncalves}, Thiago S. and {Egami}, Eiichi and {Kade}, Kiana and {Rana}, Rahul and {Sommovigo}, Laura and {Stanley}, Flora and {Stark}, Daniel P.}, title = {{Highly-ionized gas in lensed z = 6.027 Little Red Dot seen through [OIII] 88$μ$m with ALMA}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.05097}, pages = {arXiv:2512.05097}, archiveprefix = {arXiv}, eprint = {2512.05097}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251205097K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, non-agn, spectroscopy}, month_numeric = {12} }

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Challenging the Active Galactic Nucleus Scenario for JWST/NIRSpec Little Red Dot and Non─Little Red Dot Broad H\ensuremathα Emitters in Light of Nondetection of NIRCam Photometric Variability and X-Ray

Mitsuru Kokubo and Yuichi Harikane

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

JWST has uncovered a substantial population of high-z (z \ensuremath≳ 4) galaxies exhibiting broad H\ensuremathα emission lines with a full width at half- maximum exceeding 1000 km s^\ensuremath-1. This population consists of a well-known subset called little red dots (LRDs) and the remaining non-LRDs. If all of these broad H\ensuremathα emitters were attributed to type 1─1.9 active galactic nuclei (AGNs), it would imply a significantly higher number density of low-luminosity AGNs than extrapolated from that of more luminous AGNs. Here, we have examined the rest-frame ultraviolet (UV)-optical flux variability of three LRD and two non-LRD broad H\ensuremathα emitters using multiepoch, multiband JWST/NIRCam imaging data. The rest-frame temporal sampling interval of the NIRCam data (\ensuremath∼400─500 days/(1 + z)) is comparable to typical variability timescales of AGNs with black hole masses of M_BH \ensuremath∼ 10^7 M_\ensuremath⊙; thus, the flux variations should be detectable if AGNs were present. However, no measurable flux variation over the rest-frame wavelength range of \ensuremathλ_rest \ensuremath∼ 1500─9000 Å has been detected, placing stringent upper limits on the variability amplitudes. This result, combined with the X-ray faintness confirmed by the ultradeep Chandra data, indicates that, under the AGN scenario, we need to postulate peculiar Compton-thick broad-line AGNs with either (a) an intrinsically nonvariable AGN disk continuum, (b) a host galaxy-dominated continuum, or (c) scattering-dominated AGN emission. Alternatively, (d) they could be non-AGNs where the broad-line emission originates from unusually fast and dense/low- metallicity star formation-driven outflows or inelastic Raman scattering of stellar UV continua by neutral hydrogen atoms.

@article{2025ApJ...995...24K, author = {{Kokubo}, Mitsuru and {Harikane}, Yuichi}, title = {{Challenging the Active Galactic Nucleus Scenario for JWST/NIRSpec Little Red Dot and Non─Little Red Dot Broad H{\ensuremath{\alpha}} Emitters in Light of Nondetection of NIRCam Photometric Variability and X-Ray}}, journal = {\apj}, keywords = {High-redshift galaxies, Active galactic nuclei, 734, 16, Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = dec, volume = {995}, number = {1}, eid = {24}, pages = {24}, doi = {10.3847/1538-4357/ae119e}, archiveprefix = {arXiv}, eprint = {2407.04777}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...995...24K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, non-agn, variability, x-ray}, month_numeric = {12} }

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X-ray properties of massive compact relic galaxies

Orsolya E. Kovács, Norbert Werner, Ákos Bogdán, and 1 more author

Astronomy & Astrophysics, Dec 2025

Abs DOI ADS arXiv

We present the X-ray analysis of seven local compact elliptical galaxies (cEGs), selected for their morphological resemblance to high- redshift red nuggets. As likely descendants of the red nugget population, cEGs offer a unique window into the early Universe, enabling the study of early galaxy evolution and the interplay between black holes, stellar bulges, and dark matter halos. Using data from Chandra and XMM-Newton, we investigate the properties of the hot gaseous halos in cEGs. Two galaxies ─ MRK 1216 and PGC 32873 ─ host luminous, spatially extended X-ray atmospheres, allowing us to derive radial thermodynamic profiles. For MRK 1216, we performed high-resolution spectral modeling with RGS data, which hints at super-solar \ensuremathα/Fe abundance ratios. The remaining galaxies show either faint or undetected X-ray halos, though several display AGN-like (active galactic nucleus) power-law emission. In the context of local scaling relations, cEGs show only mild deviations from the general galaxy population, exhibiting a slightly steeper M_★ \ensuremath- L_X relation and occupying the lower boundary of the M_★─M_vir relation. These trends suggest that high- redshift red nuggets may also host a diverse range of X-ray atmospheres. We speculate that the compactness of cEGs may trace back to the population of ’little red dots’ (LRDs), hinting at a potential link between LRDs, red nuggets, and compact relic galaxies in the local Universe.

@article{2025A&A...704A.196K, author = {{Kov{\'a}cs}, Orsolya E. and {Werner}, Norbert and {Bogd{\'a}n}, {\'A}kos and {de Plaa}, Jelle}, title = {{X-ray properties of massive compact relic galaxies}}, journal = {\aap}, keywords = {galaxies: elliptical and lenticular, cD, galaxies: evolution, galaxies: formation, X-rays: galaxies}, year = {2025}, month = dec, volume = {704}, eid = {A196}, pages = {A196}, doi = {10.1051/0004-6361/202555575}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...704A.196K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, local counterpart, morphology, spectroscopy, x-ray}, eprint = {2505.14768}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {12} }

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From ASTRID to BRAHMA – The role of overmassive black holes in little red dots in cosmological simulations

Patrick LaChance, Aklant Kumar Bhowmick, Rupert A. C. Croft, and 8 more authors

arXiv e-prints, Dec 2025

Abs ADS arXiv

We leverage the overmassive black holes (\rm M_BH/M_∗ \approx0.1) present in a realization of the BRAHMA cosmological hydrodynamic simulation suite to investigate their role in the emission of the unique “little red dot” (LRD) objects identified by the James Webb Space Telescope (JWST). We find that these black holes can produce LRD-like observables when their emission is modeled with a dense gas cloud shrouding the active galactic nucleus (AGN). Between redshifts 5 and 8, we find the number density of LRDs in this simulation to be \rm 2.04 \pm 0.32 \times 10^-4 \space Mpc^-3, which is broadly consistent with current estimates for the total LRD population from JWST. Their emission in the rest-frame visible spectrum is dominated by their AGN, which induces the red color indicative of LRDs via a very strong Balmer break. Additionally, the elevated mass of the black holes reduces the temperature of their accretion discs. This shifts the peak of the AGN emission towards longer wavelengths, and increases their brightness in the rest-frame visible spectrum relative to lower mass black holes accreting at the same rate. These simulated LRDs have very minimal dust attenuation (\rm A_V = 0.21 \pm 0.12), limiting the amount of dust re-emission that would occur in the infrared, making them very likely to fall below the observed detection limits from observatories like the Atacama Large Millimeter Array (ALMA). In contrast to the BRAHMA box, the ASTRID simulation produces systematically smaller black holes and predicts LRD number densities that are more than two orders of magnitude lower than current measurements. We therefore conclude that the presence of black holes that are overmassive relative to their host galaxy, and enshrouded in dense gas, is necessary for AGN-dominated LRD models to reproduce both the observed properties and abundances of JWST LRD populations.

@article{2025arXiv251213957L, author = {{LaChance}, Patrick and {Bhowmick}, Aklant Kumar and {Croft}, Rupert A. C. and {Di Matteo}, Tiziana and {Zhou}, Yihao and {Pacucci}, Fabio and {Blecha}, Laura and {Torrey}, Paul and {Ni}, Yueying and {Chen}, Nianyi and {Bird}, Simeon}, title = {{From ASTRID to BRAHMA -- The role of overmassive black holes in little red dots in cosmological simulations}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.13957}, pages = {arXiv:2512.13957}, archiveprefix = {arXiv}, eprint = {2512.13957}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251213957L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, sed, simulation}, month_numeric = {12} }

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Super-Eddington accretion in high-redshift quasar hosts: Black-hole-driven outflows, galaxy quenching, and the nature of little red dots

Giada Quadri, Alessandro Trinca, Alessandro Lupi, and 2 more authors

Astronomy & Astrophysics, Dec 2025

Abs DOI ADS arXiv

The advent of the James Webb Space Telescope has revolutionised our understanding of the high-redshift Universe through its detection of bright, massive galaxies up to z \ensuremath≳ 10 and its identification of peculiar sources called ’little red dots’ (LRDs). The origin of both classes of objects remains uncertain but is likely linked to the formation and early growth of the first massive black holes (MBHs), which may be more easily explained by invoking phases of super-Eddington accretion. In this study, we used a state-of- the-art zoom-in cosmological simulation of a quasar host to investigate whether these objects could resemble any of the peculiar sources observed with JWST during their assembly. We find that the impact of MBH feedback on star formation is typically moderate, with outflows preferentially escaping perpendicular to the galactic disc. However, for approximately ten percent of the galaxy’s lifetime, the system enters a distinct quenched phase following rapid MBH growth driven by super-Eddington accretion. This phase culminates in a powerful feedback event, during which the MBH jet and disc-driven winds interact directly with the galactic disc and carve out a central cavity. We also find that, during the history of the quasar host progenitor, the spectral properties of the system can resemble both LRDs and quenched galaxies, depending on the specific evolutionary stage considered. These findings suggest that both conditions may represent transient phases in the life cycle of high-redshift galaxies.

@article{2025A&A...704A.248Q, author = {{Quadri}, Giada and {Trinca}, Alessandro and {Lupi}, Alessandro and {Colpi}, Monica and {Volonteri}, Marta}, title = {{Super-Eddington accretion in high-redshift quasar hosts: Black-hole-driven outflows, galaxy quenching, and the nature of little red dots}}, journal = {\aap}, keywords = {accretion, accretion disks, galaxies: evolution, galaxies: formation, quasars: supermassive black holes}, year = {2025}, month = dec, volume = {704}, eid = {A248}, pages = {A248}, doi = {10.1051/0004-6361/202555423}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...704A.248Q}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, simulation}, eprint = {2505.05556}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {12} }

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The Clustering of Little Red Dots from Ultra-Strongly Self-Interacting Dark Matter

M. Grant Roberts, Aarna Garg, Tesla Jeltema, and 1 more author

arXiv e-prints, Dec 2025

Abs ADS arXiv

We predict the effective clustering bias parameter, b_\rmeff, at z\sim5 for Little Red Dots (LRDs) seeded by Ultra-Strongly Self-Interacting Dark Matter (uSIDM). From our model, we find that b_\rmeff\sim4.5, thus we infer that LRDs seeded by uSIDM would populate halos of typical masses ∼8\times10^10~M_⊙; this bias factor is consistent with LRDs being a distinct population from high redshift quasars. To the extent that we are aware, this is the first formation-based theoretical prediction of LRD clustering from a model consistent with the LRD mass function. We find that this bias and clustering is insensitive to a wide range of the underlying uSIDM microphysics parameters, including the uSIDM cross-section σ/m and uSIDM fraction f. This is therefore a robust prediction from the uSIDM model, and will allow for direct probes of the uSIDM paradigm as the origin of LRDs in the next few years. Upcoming \textbackslashtexttt{JWST} observations will constrain the population of LRDs, including directly measuring their clustering.

@article{2025arXiv251218000R, author = {{Roberts}, M. Grant and {Garg}, Aarna and {Jeltema}, Tesla and {Profumo}, Stefano}, title = {{The Clustering of Little Red Dots from Ultra-Strongly Self-Interacting Dark Matter}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, High Energy Physics - Phenomenology}, year = {2025}, month = dec, eid = {arXiv:2512.18000}, pages = {arXiv:2512.18000}, archiveprefix = {arXiv}, eprint = {2512.18000}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251218000R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {clustering, early universe, jwst, non-agn, theory}, month_numeric = {12} }

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Cosmic stillness: high quiescent galaxy fractions across upper mass scales in the early Universe to z = 7 with JWST

Tobias A. Russell, Neva Dobric, Nathan J. Adams, and 25 more authors

Monthly Notices of the Royal Astronomical Society, Dec 2025

Abs DOI ADS arXiv

We present a detailed investigation into the abundance and morphology of high-redshift quenched galaxies at using James Webb Space Telescope data in the NEP, CEERS, and JADES fields. Within these fields, we identify 90 candidate passive galaxies using specific star formation rates modelled with the BAGPIPES spectral energy distribution fitting code, which is more effective at identifying recently quenched systems than the classical UVJ method, which specializes in quenched objects 1 Gyr. With this sample of galaxies, we find number densities broadly consistent with other works and a rapidly evolving passive fraction of high-mass galaxies ( 9.5) in the range . We find that the fraction of galaxies with low star formation rates and mass 9.5 10.5 decreases from 25 per cent at to 2 per cent at . Our passive sample of galaxies is shown to exhibit more compact light profiles compared to star-forming counterparts and some exhibit traces of active galactic nucleus activity through detections in either the X-ray or radio. At the highest redshifts () passive selections start to include examples of ’little red dots’, which complicates any conclusions until their nature is better understood.

@article{2025MNRAS.544.4482R, author = {{Russell}, Tobias A. and {Dobric}, Neva and {Adams}, Nathan J. and {Conselice}, Christopher J. and {Austin}, Duncan and {Harvey}, Thomas and {Trussler}, James A. A. and {Ferreira}, Leonardo and {Westcott}, Lewi and {Harris}, Honor and {Windhorst}, Rogier A. and {Coe}, Dan and {Cohen}, Seth H. and {Driver}, Simon P. and {Frye}, Brenda and {Grogin}, Norman A. and {Hathi}, Nimish P. and {Jansen}, Rolf A. and {Koekemoer}, Anton M. and {Marshall}, Madeline A. and {Ortiz}, III, Rafael and {Pirzkal}, Nor and {Robotham}, Aaron and {Ryan}, Jr., Russell E. and {Summers}, Jake and {D'Silva}, Jordan C. J. and {Willmer}, Christopher N. A. and {Yan}, Haojing}, title = {{Cosmic stillness: high quiescent galaxy fractions across upper mass scales in the early Universe to z = 7 with JWST}}, journal = {\mnras}, keywords = {galaxies: evolution, galaxies: high-redshift, galaxies: photometry, galaxies: star formation, galaxies: statistics, galaxies: structure, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = dec, volume = {544}, number = {4}, pages = {4482-4504}, doi = {10.1093/mnras/staf1916}, archiveprefix = {arXiv}, eprint = {2412.11861}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.544.4482R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, morphology, sample selection, sed}, month_numeric = {12} }

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Little Red Dots at an Inflection Point: Ubiquitous V-shaped Turnover Consistently Occurs at the Balmer Limit

David J. Setton, Jenny E. Greene, Anna de Graaff, and 18 more authors

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

Among the most puzzling early discoveries of JWST are “little red dots” (LRDs), compact red sources that host broad Balmer emission lines, and in many cases exhibit a “V-shaped” change in slope in the rest-optical. The physical properties of LRDs currently have order-of-magnitude uncertainties, because models to explain the continuum of these sources differ immensely. Here, we leverage the complete selection of red sources in the RUBIES program, supplemented with public PRISM spectra, to study the origin of this V shape. By fitting a broken power law with a flexible inflection point, we find that a large fraction of red H\ensuremathα emitters at 2 < z < 6 exhibit a strong change in slope, and that all strong inflections appear associated with the Balmer limit (0.3645 \ensuremathμm). Using a simple model of a reddened active galactic nucleus (AGN) with an unobscured scattered-light component, we demonstrate that the observed V shape in LRDs is unlikely to occur at any specific wavelength if the entire continuum is dominated by light from a power-law AGN continuum. In contrast, models with an intrinsic feature at the Balmer limit, such as those that are dominated by an evolved stellar population, can produce the observed spectral shapes, provided that a reddened component picks up sufficiently redward of the break. While no model can comfortably explain the full LRD spectral energy distribution, the common inflection location suggests that a single component consistently dominates the rest-frame UV optical in LRDs, and that this component is associated with T \ensuremath∼ 10^4 K hydrogen.

@article{2025ApJ...995..118S, author = {{Setton}, David J. and {Greene}, Jenny E. and {de Graaff}, Anna and {Ma}, Yilun and {Leja}, Joel and {Matthee}, Jorryt and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Cleri}, Nikko J. and {Katz}, Harley and {Labbe}, Ivo and {Maseda}, Michael V. and {McConachie}, Ian and {Miller}, Tim B. and {Price}, Sedona H. and {Suess}, Katherine A. and {van Dokkum}, Pieter and {Wang}, Bingjie and {Weibel}, Andrea and {Whitaker}, Katherine E. and {Williams}, Christina C.}, title = {{Little Red Dots at an Inflection Point: Ubiquitous V-shaped Turnover Consistently Occurs at the Balmer Limit}}, journal = {\apj}, keywords = {Active galactic nuclei, High-redshift galaxies, Galaxy evolution, Near infrared astronomy, 16, 734, 594, 1093}, year = {2025}, month = dec, volume = {995}, number = {1}, eid = {118}, pages = {118}, doi = {10.3847/1538-4357/ae1500}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...995..118S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, non-agn, sed, spectroscopy}, eprint = {2411.03424}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {12} }

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Probing the Physical Origin of the Balmer Decrement in the Broad-line Region of Nearby Active Galactic Nuclei via Spectral Variability

Suyeon Son, Minjin Kim, Luis C. Ho, and 1 more author

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

To investigate the physical origin of the Balmer decrement in the broad- line region of active galactic nuclei (AGNs), we measure the temporal variability of the fluxes of the broad H\ensuremathβ and H\ensuremathα emission lines using multiepoch spectroscopic data of low-redshift AGNs from the Sloan Digital Sky Survey. The analysis of the mean spectra reveals that the Balmer decrement shows no correlation with AGN luminosity, while it is inversely correlated with the Eddington ratio. However, the temporal variation of the Balmer decrement in individual objects exhibits an even stronger anticorrelation with AGN luminosity, suggesting that the change in AGN luminosity plays a dominant role in determining the Balmer decrement. By comparing the temporal evolution of the Balmer decrement with the continuum color, we find that reddening due to the AGN itself may not be the primary factor. Instead, radiative transfer effects and excitation mechanisms, which deviate from the Case B recombination, appear to be critical for the variation of the Balmer decrement. These results provide useful insights into the underlying physics of changing-look AGNs and high-z AGNs, such as the “little red dots,” which exhibit extreme values of the Balmer decrement that can be misinterpreted as evidence for dust.

@article{2025ApJ...995...37S, author = {{Son}, Suyeon and {Kim}, Minjin and {Ho}, Luis C. and {Li}, Ruancun}, title = {{Probing the Physical Origin of the Balmer Decrement in the Broad-line Region of Nearby Active Galactic Nuclei via Spectral Variability}}, journal = {\apj}, keywords = {Active galaxies, 17, Astrophysics of Galaxies}, year = {2025}, month = dec, volume = {995}, number = {1}, eid = {37}, pages = {37}, doi = {10.3847/1538-4357/ae1ef1}, archiveprefix = {arXiv}, eprint = {2511.07714}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...995...37S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, spectroscopy, theory, variability}, month_numeric = {12} }

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Discovery of a Little Red Dot Candidate at z \ensuremath≳ 10 in COSMOS-web Based on MIRI-NIRCam Selection

Takumi S. Tanaka, Hollis B. Akins, Yuichi Harikane, and 64 more authors

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

JWST has revealed a new high-redshift population called little red dots (LRDs). Since LRDs may be in the early phase of black hole growth, identifying them in the early Universe is crucial for understanding the formation of the first supermassive black holes. However, no robust LRD candidates have been identified at z > 10, because commonly used NIRCam photometry covers wavelengths up to \ensuremath∼5 \ensuremathμm and is insufficient to capture the characteristic V-shaped spectral energy distributions (SEDs) of LRDs. In this study, we present the first search for z \ensuremath≳ 10 LRD candidates using both NIRCam and MIRI imaging from COSMOS-Web, which provides the largest joint NIRCam-MIRI coverage to date (0.20 deg^2). Taking advantage of MIRI/F770W to remove contaminants, we identify one robust candidate, CW-LRD-z10 at zphot=10.5\ensuremath-0.6+0.7 with MUV=\ensuremath-19.9\ensuremath-0.2+0.1mag. CW-LRD-z10 exhibits a compact morphology, a distinct V-shaped SED, and a nondetection in F115W, all consistent with being an LRD at z \ensuremath∼ 10. Based on this discovery, we place the first constraint on the number density of LRDs at z \ensuremath∼ 10 with M_UV \ensuremath∼ \ensuremath-20 of 1.2\ensuremath-1.0+2.7\texttimes10 ensuremath-6Mpc\ensuremath-3mag\ensuremath-1, suggesting that the fraction of LRDs among the overall galaxy population increases with redshift, reaching \ensuremath∼3% at z \ensuremath∼ 10. Although deep spectroscopy is necessary to confirm the redshift and the nature of CW-LRD-z10, our results imply that LRDs may be a common population at z > 10, playing a key role in the first supermassive black hole formation.

@article{2025ApJ...995...21T, author = {{Tanaka}, Takumi S. and {Akins}, Hollis B. and {Harikane}, Yuichi and {Silverman}, John D. and {Casey}, Caitlin M. and {Inayoshi}, Kohei and {Schindler}, Jan-Torge and {Shimasaku}, Kazuhiro and {Kocevski}, Dale D. and {Onoue}, Masafusa and {Faisst}, Andreas L. and {Robertson}, Brant E. and {Kokorev}, Vasily and {Shuntov}, Marko and {Koekemoer}, Anton M. and {Franco}, Maximilien and {Egami}, Eiichi and {Liu}, Daizhong and {Taylor}, Anthony J. and {Kartaltepe}, Jeyhan S. and {Bosman}, Sarah E. I. and {Champagne}, Jaclyn B. and {Kakiichi}, Koki and {Harish}, Santosh and {Zhang}, Zijian and {Newman}, Sophie L. and {Kakkad}, Darshan and {Fei}, Qinyue and {Fujimoto}, Seiji and {Li}, Mingyu and {Finkelstein}, Steven L. and {Li}, Zi-Jian and {Lambrides}, Erini and {Sommovigo}, Laura and {Zavala}, Jorge A. and {Ito}, Kei and {Liu}, Zhaoxuan and {Treister}, Ezequiel and {Aravena}, Manuel and {Gozaliasl}, Ghassem and {Zhang}, Haowen and {Hatamnia}, Hossein and {Umeda}, Hiroya and {Inoue}, Akio K. and {Yang}, Jinyi and {Ando}, Makoto and {Arita}, Junya and {Ding}, Xuheng and {Matsui}, Suin and {Shibanuma}, Yuki and {Magdis}, Georgios and {Zhuang}, Mingyang and {Fan}, Xiaohui and {Li}, Zihao and {Liu}, Weizhe and {Lyu}, Jianwei and {Rhodes}, Jason and {Toft}, Sune and {Wang}, Feige and {Zou}, Siwei and {Arango-Toro}, Rafael C. and {Battisti}, Andrew J. and {Gillman}, Steven and {Khostovan}, Ali Ahmad and {Long}, Arianna S. and {Mobasher}, Bahram and {Sanders}, David B.}, title = {{Discovery of a Little Red Dot Candidate at z {\ensuremath{\gtrsim}} 10 in COSMOS-web Based on MIRI-NIRCam Selection}}, journal = {\apj}, keywords = {Active galactic nuclei, Galaxy evolution, High-redshift galaxies, Galaxy formation, 16, 594, 734, 595, Astrophysics of Galaxies}, year = {2025}, month = dec, volume = {995}, number = {1}, eid = {21}, pages = {21}, doi = {10.3847/1538-4357/ae145f}, archiveprefix = {arXiv}, eprint = {2508.00057}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...995...21T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, photometry, sed}, month_numeric = {12} }

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Black hole stars really do exist

Alex Wilkins

New Scientist, Dec 2025

Abs DOI ADS

Mysterious ’little red dots’ seen by the James Webb Space Telescope can be explained by a new kind of black hole enshrouded in an enormous ball of glowing gas, finds Alex Wilkins

@article{2025NewSc.268....6W, author = {{Wilkins}, Alex}, title = {{Black hole stars really do exist}}, journal = {New Scientist}, year = {2025}, month = dec, volume = {268}, number = {3575}, pages = {6-6}, doi = {10.1016/S0262-4079(25)02052-4}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NewSc.268....6W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, jwst, non-agn, theory}, month_numeric = {12} }

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Born in the Dark: The Catastrophic Collapse of Fuzzy Dark Matter Solitons as the Origin of Little Red Dots

Tak-Pong Woo

arXiv e-prints, Dec 2025

Abs ADS arXiv

JWST surveys have uncovered a population of compact, red sources (“Little Red Dots,” LRDs) at z \ge 5 that exhibit broad Balmer emission yet remain X-ray faint, implying heavy obscuration with N_H \ge 10^24 cm^-2. We propose that LRDs may trace a short-lived, obscured phase associated with rapid baryonic inflow inside the deep solitonic cores of fuzzy dark matter (FDM) halos. Combining the soliton size scaling with (i) the observed compact radii (r_e ∼30-100 pc) and (ii) the requirement that Compton-thick columns be achievable within a region of order the core radius, we find that particle masses m few \times 10^-22 eV are plausible for soliton masses M_s ∼10^8 - 10^9 M_⊙; we adopt m_22=2 as a fiducial choice. A conservative mass-budget estimate for the obscuring column, together with isothermal hydrostatic stratification, indicates that configurations reaching N_H \ge 10^24 - 10^25 cm^-2 require densities for which radiative losses (cooling and/or diffusion) occur faster than the dynamical time, suggesting that a long-lived static hot atmosphere is unlikely (an “Opacity Crisis”) and that rapid inflow or radiation-pressure-driven evolution is favored. Using 512^3 pseudo-spectral Schrödinger-Poisson simulations of idealized soliton mergers, we illustrate that compact, high- density soliton cores can form via violent relaxation under representative scalings. We discuss observational implications and tests, and outline the need for future radiation- hydrodynamic modeling to predict demographics and detailed spectra.

@article{2026arXiv260100044W, author = {{Woo}, Tak-Pong}, title = {{Born in the Dark: The Catastrophic Collapse of Fuzzy Dark Matter Solitons as the Origin of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2601.00044}, pages = {arXiv:2601.00044}, archiveprefix = {arXiv}, eprint = {2601.00044}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260100044W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, simulation, theory}, month_numeric = {12} }

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High-Redshift Galaxy Candidates at z > 6 as Revealed by JWST Observations of MACS0647

Keduse Worku, Tiger Yu-Yang Hsiao, Dan Coe, and 9 more authors

arXiv e-prints, Dec 2025

Abs ADS arXiv

We present a catalog of 57 high-redshift z>6 galaxy candidates, including 14 spectroscopic confirmations (z = 6.10 – 9.25), 2 Little Red Dots (z = 4.77, 5.81), and 2 interlopers (z = 3.23, 3.72), based on \textbackslashJWST\NIRCam imaging (7 filters), NIRSpec spectroscopy (PRISM and G395H), and archival \textbackslashHST\imaging (17 filters) of the strong lensing galaxy cluster MACS0647. Our highest redshift confirmation (z = 9.25) is an Extremely Blue Galaxy (presented in\raisebox-0.5ex~\textbackslashcitealt{Yanagis awa2024}), and here we identify a spectral turnover likely due to damped Lyman-α. We identify an overdensity of galaxies with spectroscopic redshifts z = 6.1, confirming the z ∼6 overdensity identified in \textbackslashHST\images. In one of these galaxies, our high-resolution G395H spectroscopy reveals two spatially resolved components with a velocity difference of \sim90 km/s; if these components are gravitationally bound, this would imply a dynamical mass on the order of ∼10^8 M_⊙given their projected separation. We present spectral line fluxes, widths, and derived physical properties, including stellar masses (10^8 - 10^9 \mathrmM_⊙) and metallicities (10% - 40% \mathrmZ_⊙) for our spectroscopic sample. We note half of our NIRSpec data was obtained with standard 3-slitlet nods and half was obtained with single slitlets yielding similar results, demonstrating the power to observe more sources on a densely packed NIRSpec MSA.

@article{2025arXiv251211985W, author = {{Worku}, Keduse and {Hsiao}, Tiger Yu-Yang and {Coe}, Dan and {Abdurro'uf} and {Resseguier}, Tom and {Larson}, Rebecca L. and {Antwi-Danso}, Jacqueline and {Brammer}, Gabriel and {Kokorev}, Vasily and {Bradley}, Larry D. and {Furtak}, Lukas J. and {Oguri}, Masamune}, title = {{High-Redshift Galaxy Candidates at z > 6 as Revealed by JWST Observations of MACS0647}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = dec, eid = {arXiv:2512.11985}, pages = {arXiv:2512.11985}, archiveprefix = {arXiv}, eprint = {2512.11985}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251211985W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {catalog, early universe, emission lines, jwst, spectroscopy}, month_numeric = {12} }

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Radiation GRMHD Models of Accretion onto Stellar-mass Black Holes. I. Survey of Eddington Ratios

Lizhong Zhang, James M. Stone, Patrick D. Mullen, and 3 more authors

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

We summarize results from a survey of radiation-dominated black hole accretion flows across a wide range of mass accretion rates, as well as two values of black hole spin and initial magnetic field geometry. These models apply an algorithm targeting direct solutions to the radiation transport equation in full general relativity and have been enabled by access to modern exascale computing systems. Super-Eddington accretion flows form geometrically thick radiation-pressure-supported disks that drive powerful equatorial outflows. A narrow funnel-shaped photosphere in the inner region results in very low radiative efficiencies in this regime. The structure of near- and sub- Eddington accretion depends on whether there is net vertical magnetic flux at the midplane of the disk. With net flux, the disk forms a thin, dense layer at the midplane surrounded by a magnetically dominated corona, whereas without net flux, the disk remains magnetically dominated everywhere. Although none of our models achieve the magnetically arrested disk regime, those with net vertical flux and a rapidly spinning black hole still produce powerful relativistic jets. Our calculations adopt simple opacity models (with scalings appropriate to stellar-mass black hole accretion). We discuss the application of our results to observations of X-ray binaries and ultraluminous X-ray sources such as Cyg X-3 and SS433. We also speculate on the application of our super-Eddington models to the interpretation of little red dots recently discovered by JWST.

@article{2025ApJ...995...26Z, author = {{Zhang}, Lizhong and {Stone}, James M. and {Mullen}, Patrick D. and {Davis}, Shane W. and {Jiang}, Yan-Fei and {White}, Christopher J.}, title = {{Radiation GRMHD Models of Accretion onto Stellar-mass Black Holes. I. Survey of Eddington Ratios}}, journal = {\apj}, keywords = {Radiative magnetohydrodynamics, General relativity, Black hole physics, Accretion, Ultraluminous x-ray sources, X-ray binary stars, 2009, 641, 159, 14, 2164, 1811, High Energy Astrophysical Phenomena}, year = {2025}, month = dec, volume = {995}, number = {1}, eid = {26}, pages = {26}, doi = {10.3847/1538-4357/ae0f91}, archiveprefix = {arXiv}, eprint = {2506.02289}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...995...26Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, jwst, simulation, theory, x-ray}, month_numeric = {12} }

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Little red dot variability over a century reveals black hole envelope via a giant Einstein cross

Zijian Zhang, Mingyu Li, Masamune Oguri, and 79 more authors

arXiv e-prints, Dec 2025

Abs DOI ADS arXiv

“Little red dots” (LRDs) represent a new population of astronomical objects uncovered by JWST whose nature remains debated. Although many LRDs are suspected as active galactic nuclei (AGN), they show little variability on days-years timescales. We report the discovery of two gravitationally lensed LRDs at redshift \sim4.3 behind the cluster RXCJ2211-0350, one of which (RX1) is quadruply imaged with time delays spanning \sim130 years. RX1 exhibits intrinsic color and brightness variations of up to 0.7 magnitude among its images. These changes are consistent with blackbody-temperature variations of a photosphere, indicating long-term variability analogous to Cepheid-like pulsations but in a far more extended (R ∼2000 AU) and massive (M rsim 10^6 \,M_⊙) systems. These results suggest LRDs as a distinct class of AGN with stellar-like envelopes.

@article{2025arXiv251205180Z, author = {{Zhang}, Zijian and {Li}, Mingyu and {Oguri}, Masamune and {Lin}, Xiaojing and {Inayoshi}, Kohei and {Cerny}, Catherine and {Coe}, Dan and {Diego}, Jose M. and {Fujimoto}, Seiji and {Jiang}, Linhua and {Mahler}, Guillaume and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Sharon}, Keren and {Shen}, Yue and {Zitrin}, Adi and {Abdurro'uf} and {Akins}, Hollis and {Allingham}, Joseph F. V. and {Amor{\'\i}n}, Ricardo and {Asada}, Yoshihisa and {Atek}, Hakim and {Bauer}, Franz E. and {Brada{\v{c}}}, Maru{\v{s}}a and {Bradley}, Larry D. and {Cai}, Zheng and {Cantalupo}, Sebastiano and {Conselice}, Christopher and {Dai}, Liang and {Dayal}, Pratika and {Egami}, Eiichi and {Eisenstein}, Daniel J. and {Faisst}, Andreas L. and {Fan}, Xiaohui and {Fei}, Qinyue and {Frye}, Brenda L. and {Fudamoto}, Yoshinobu and {Furtak}, Lukas J. and {Golubchik}, Miriam and {Gonz{\'a}lez-Otero}, Mauro and {Harikane}, Yuichi and {Hsiao}, Tiger Yu-Yang and {Jim{\'e}nez-Teja}, Yolanda and {Kartaltepe}, Jeyhan S. and {Kiyota}, Tomokazu and {Koekemoer}, Anton M. and {Kohno}, Kotaro and {Kokorev}, Vasily and {Kumari}, Nimisha and {Labbe}, Ivo and {Lagos}, Claudia D. P. and {Larison}, Conor and {Liang}, Yongming and {Lucas}, Ray A. and {Lyu}, Jianwei and {Martis}, Nicholas S. and {Magdis}, Georgios E. and {Messa}, Matteo and {Nakane}, Minami and {Noirot}, Ga{\"e}l and {Ortiz}, III, Rafael and {Ouchi}, Masami and {Pierel}, Justin D. R. and {Postman}, Marc and {Reddy}, Naveen and {Ricotti}, Massimo and {Schaerer}, Daniel and {Schneider}, Raffaella and {Steidel}, Charles C. and {Tee}, Wei Leong and {Tripodi}, Roberta and {Trussler}, James A. A. and {Umeda}, Hiroya and {Valentino}, Francesco and {Vanzella}, Eros and {Wang}, Feige and {Windhorst}, Rogier and {Wu}, Yunjing and {Wu}, Zihao and {Yanagisawa}, Hiroto and {Yang}, Jinyi and {Sun}, Fengwu}, title = {{Little red dot variability over a century reveals black hole envelope via a giant Einstein cross}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.05180}, pages = {arXiv:2512.05180}, doi = {10.48550/arXiv.2512.05180}, archiveprefix = {arXiv}, eprint = {2512.05180}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251205180Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, photometry, variability}, month_numeric = {12} }

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Ruling out dominant electron scattering in Little Red Dots’ Rosetta Stone using multiple hydrogen lines

Matilde Brazzini, Francesco D’Eugenio, Roberto Maiolino, and 4 more authors

Monthly Notices of the Royal Astronomical Society, Nov 2025

Abs DOI ADS arXiv

Most little red dots (LRDs) hosting active galactic nuclei (AGNs) show broad emission, which recent studies ascribe to scattering off free electrons within an ionized medium embedding the broad-line region (BLR), rather than directly from the BLR itself. If correct, this model would imply intrinsically narrower broad line widths, leading to black hole masses that are up to two orders of magnitude smaller than what is inferred when assuming that the whole broad line emission comes from the BLR. To test this, we present a joint analysis of multiple hydrogen recombination lines in the ’Rosetta Stone’ AGNs, the brightest known LRD at z = 2.26. We show that , , and have different spectral profiles, which is inconsistent with the predictions of the simple scattering scenario. Additionally, we test a variety of exponential models and show that none of them can simultaneously reproduce all three line profiles with physically plausible parameters. The inadequacy of these models for the Rosetta Stone implies that the scenario of electron scattering by an ionized medium embedding the BLR is not universally applicable to LRDs and AGNs, and therefore provides a counterexample to the claim of a universal and systematic overestimation of black hole masses.

@article{2025MNRAS.544L.167B, author = {{Brazzini}, Matilde and {D'Eugenio}, Francesco and {Maiolino}, Roberto and {Juod{\v{z}}balis}, Ignas and {Ji}, Xihan and {Scholtz}, Jan and {Chang}, Seok-Jun}, title = {{Ruling out dominant electron scattering in Little Red Dots' Rosetta Stone using multiple hydrogen lines}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: high-redshift, quasars: supermassive black holes}, year = {2025}, month = nov, volume = {544}, number = {1}, pages = {L167-L173}, doi = {10.1093/mnrasl/slaf116}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.544L.167B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, non-jwst, spectroscopy}, eprint = {2507.08929}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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High-velocity Outflows in [O III] Emitters at 2.5 < z < 9 from JWST NIRSpec Medium-resolution Spectroscopy

Ryan A. Cooper, Karina I. Caputi, Edoardo Iani, and 3 more authors

The Astrophysical Journal, Nov 2025

Abs DOI ADS arXiv

We identify galaxies hosting ionised-gas high-velocity outflows from the complete sample of medium-resolution (R1000) JWST/NIRSpec MSA spectroscopy taken as part of the JWST Advanced Deep Extragalactic Survey. From a total sample of 1087 [O III]_5007 emitters we identify 40 galaxies with a blue-side broadened [O III]_5007 line at 2.5 < z < 9. Of these, 34 are strong outflow candidates while 6 sources exhibit broadening potentially driven by rotating clumps. Our outflow candidate sample is mainly composed of star-forming galaxies, including \ensuremath∼65% starbursts, which span the stellar mass range 7.5 < log_10(M_*/M_\ensuremath⊙) < 11.0. It also includes two candidate type-2 active galactic nuclei and a “little red dot.” We report a median outflow velocity of 531\ensuremath-159+146 km s^\ensuremath-1 and an overall incidence rate of 3.4%. These values are significantly higher and lower, respectively, than recent similar works, which we accredit to the limiting resolution of the R1000 spectroscopy and a stricter outflow selection criterion. We find no correlation between the outflow velocity and the galaxy stellar mass or star formation rate. The median ratio between outflow velocity and escape velocity is 0.77\ensuremath-0.32+0.36, indicating that most outflows cannot escape the galaxy gravitational potentials. We do find an anti-correlation between mass loading factor and stellar mass up to M_* ≍ 10^10 M_\ensuremath⊙, with most lowest-stellar-mass (M_* < 10^9 M_\ensuremath⊙) galaxies reaching values well above unity, as is the case for local starburst galaxies.

@article{2025ApJ...994..102C, author = {{Cooper}, Ryan A. and {Caputi}, Karina I. and {Iani}, Edoardo and {Rinaldi}, Pierluigi and {Desprez}, Guillaume and {Navarro-Carrera}, Rafael}, title = {{High-velocity Outflows in [O III] Emitters at 2.5 < z < 9 from JWST NIRSpec Medium-resolution Spectroscopy}}, journal = {\apj}, keywords = {High-redshift galaxies, Galaxy winds, Galaxy evolution, Infrared astronomy, 734, 626, 594, 786}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {102}, pages = {102}, doi = {10.3847/1538-4357/ae0580}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994..102C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, kinematics, spectroscopy, starburst}, eprint = {2502.18310}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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From Feedback-Free Star Clusters to Little Red Dots via Compaction

Avishai Dekel, Dhruba Dutta Chowdhury, Sharon Lapiner, and 6 more authors

arXiv e-prints, Nov 2025

Abs ADS arXiv

We address the origin of the Little Red Dots (LRDs) seen by JWST at cosmic morning (z \!=\! 4 \!-\! 8) as compact stellar systems with over-massive black holes (BHs). We propose that LRDs form naturally after feedback-free starbursts (FFB) in thousands of star clusters and following wet compaction. Analytically, we show how the clusters enable efficient dry migration of stars and BHs to the galaxy center by two-body segregation and dynamical friction against the disk. The clusters merge to form compact central clusters as observed. Mutual tidal stripping does not qualitatively affect the analysis. The young, rotating clusters are natural sites for the formation of BH seeds via rapid core collapse. The migrating clusters carry the BH seeds, which merge into central super-massive BHs (SMBHs). Compactions are required to deepen the potential wells such that the SMBHs are retained after post-merger gravitational-wave recoils, locked to the galaxy centers. Using cosmological simulations at different epochs, with different codes and physical recipes, we evaluate the additional growth of LRD-matching compact central stellar systems by global compaction events. Adding to the dry growth by cluster mergers, the compactions can increase the escape velocities to retain the SMBHs. The LRDs appear at z \!∼\! 8, after the formation of FFB clusters, and disappear after z \!∼\! 4 when the stellar mass is above 10^9 M_⊙by growing post-compaction blue disks around the nuclear LRDs. The LRD abundance is expected to be ∼\! 10^-5 \!-\! 10^-4\,\rm Mpc^-3, increasing from z \!∼\! 4 to z\!∼\! 8.

@article{2025arXiv251107578D, author = {{Dekel}, Avishai and {Dutta Chowdhury}, Dhruba and {Lapiner}, Sharon and {Yao}, Zhiyuan and {Gilbaum}, Shmuel and {Ceverino}, Daniel and {Primack}, Joel and {Somerville}, Rachel and {Teyssier}, Romain}, title = {{From Feedback-Free Star Clusters to Little Red Dots via Compaction}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.07578}, pages = {arXiv:2511.07578}, archiveprefix = {arXiv}, eprint = {2511.07578}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251107578D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, simulation, starburst, theory}, month_numeric = {11} }

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NANOGrav 15-year gravitational-wave signals from binary supermassive black-holes seeded by primordial black holes, and implications for the origins of Little Red Dots

Mikage U. Kobayashi and Kazunori Kohri

arXiv e-prints, Nov 2025

Abs DOI ADS arXiv

In this paper, we explain the recently reported a nHz-band gravitational-wave background from NANOGrav 15-year through the merger of binary super-massive black holes with masses of 10^9 M_⊙ formed by the growth of primordial black holes. When a primordial black hole accretes at a high accretion rate, it emits a large number of high-energy photons. These heat the plasma, causing high-redshift cosmological 21cm line emission. Since this has not been detected, there is a strict upper bound on the accretion rate. We have found that with the primordial black hole abundance 10^-14 ≲f_\rm PBH ≲10^-12 and the mass 1 M_⊙ ≲m_\rm PBH ≲10^3 M_⊙, we successfully fit the nHz band gravitational wave background from NANOGrav 15-year while avoiding the 21 cm line emission. In addition, we also discuss the implication for the origins of the Little Red Dots. We propose that future observations of the gravitational wave background and the cosmological 21cm line can test this scenario.

@article{2025arXiv251104210K, author = {{Kobayashi}, Mikage U. and {Kohri}, Kazunori}, title = {{NANOGrav 15-year gravitational-wave signals from binary supermassive black-holes seeded by primordial black holes, and implications for the origins of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology}, year = {2025}, month = nov, eid = {arXiv:2511.04210}, pages = {arXiv:2511.04210}, doi = {10.48550/arXiv.2511.04210}, archiveprefix = {arXiv}, eprint = {2511.04210}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251104210K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, exotic physics, theory}, month_numeric = {11} }

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Balmer Absorption in Iron Low-ionization Broad Absorption Line Quasars

Karen M. Leighly, Sarah C. Gallagher, Hyunseop Choi, and 4 more authors

The Astrophysical Journal, Nov 2025

Abs DOI ADS arXiv

While C IV is the most common absorption line in broad absorption line quasar spectra, Balmer absorption lines (BALs) are among the rarest. We present analysis of Balmer absorption in a sample of 14 iron low-ionization BAL quasars (FeLoBALQs); eight are new identifications. We measured velocity offset, width, and apparent optical depth. The partial covering that is ubiquitous in BAL quasar spectra alters the measured Balmer optical depth ratios; accounting for this, we estimated the true H(n = 2) column density. We found the anticipated correlation between Eddington ratio and outflow speed, but it is weak in this sample because nearly all of the objects have the low outflow speeds characterizing loitering outflow FeLoBAL quasars, objects that are also found to have low accretion rates. Measurements of dN/dv, the differential column density with respect to the outflow speed, are anticorrelated with the luminosity and Eddington ratio: the strongest absorption is observed at the lowest speeds in the lowest-luminosity objects. The absorption line width is correlated with \ensuremathα_oi, the F_\ensuremathλ point-to-point slope between 5100 Å and 3 \ensuremathμm. This parameter is strongly correlated with the Eddington ratio among low-redshift quasars. BALs have been recently found in the spectra of little red dots (LRDs), a class of high-redshift objects discovered by JWST. We note suggestive similarities between LRDs and FeLoBAL quasars in the emission-line shape, the presence of steep reddening and a scattered blue continuum, the lack of hot dust emission, and X-ray weakness.

@article{2025ApJ...993..129L, author = {{Leighly}, Karen M. and {Gallagher}, Sarah C. and {Choi}, Hyunseop and {Terndrup}, Donald M. and {Voelker}, Julianna R. and {Richards}, Gordon T. and {Morabito}, Leah K.}, title = {{Balmer Absorption in Iron Low-ionization Broad Absorption Line Quasars}}, journal = {\apj}, keywords = {Broad-absorption line quasar, Quasars, 183, 1319}, year = {2025}, month = nov, volume = {993}, number = {1}, eid = {129}, pages = {129}, doi = {10.3847/1538-4357/ae04df}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...993..129L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, spectroscopy, x-ray}, eprint = {2509.07611}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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The Balmer Break and Optical Continuum of Little Red Dots from Super-Eddington Accretion

Hanpu Liu, Yan-Fei Jiang, Eliot Quataert, and 2 more authors

The Astrophysical Journal, Nov 2025

Abs DOI ADS arXiv

The physical origin of little red dots (LRDs)—compact extragalactic sources with red rest-optical continua and broad Balmer lines—remains elusive. The redness of LRDs is likely intrinsic, suggesting optically thick gas emitting at a characteristic effective temperature of \ensuremath∼5000 K. Meanwhile, many LRD spectra exhibit a Balmer break, often attributed to absorption by a dense gas shell surrounding an active galactic nucleus. Using semianalytical atmosphere models and radiation transport calculations, we show that a super- Eddington accretion system can give rise to a Balmer break and a red optical color simultaneously, without invoking external gas absorption for the break or dust reddening. The break originates from a discontinuity in opacity across the Balmer limit, similar to that of early-type stars, but the lower photosphere density of super-Eddington systems, \ensuremathρ < 10^\ensuremath-9 g cm^\ensuremath-3, implies a significant opacity contrast even at a cool photosphere temperature of \ensuremath∼5000 K. Furthermore, while accretion in the form of a standard thin disk requires fine tuning to match the optical color of LRDs, an alternative scenario of a geometrically thick, roughly spherical accretion flow implies an effective temperature of 4000 K \ensuremath≲ T_eff \ensuremath≲ 6000 K that is very insensitive to the accretion rate (analogous to the Hayashi line in stellar models). The continuum spectra from the latter scenario align with the Balmer break and optical color of currently known LRDs. We discuss the predictions of our model and the prospects for more realistic spectra based on super- Eddington accretion simulations.

@article{2025ApJ...994..113L, author = {{Liu}, Hanpu and {Jiang}, Yan-Fei and {Quataert}, Eliot and {Greene}, Jenny E. and {Ma}, Yilun}, title = {{The Balmer Break and Optical Continuum of Little Red Dots from Super-Eddington Accretion}}, journal = {\apj}, keywords = {Active galactic nuclei, Radiative transfer, Accretion, 16, 1335, 14}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {113}, pages = {113}, doi = {10.3847/1538-4357/ae0c19}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994..113L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, sed, spectroscopy, theory}, eprint = {2507.07190}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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Little Red Dots are Nurseries of Massive Black Holes

Fabio Pacucci, Lars Hernquist, and Michiko Fujii

The Astrophysical Journal, Nov 2025

Abs DOI ADS arXiv

The James Webb Space Telescope has revealed a previously unknown population of compact, red galaxies at z \ensuremath∼ 5, known as “little red dots” (LRDs). With effective radii of \ensuremath∼100 pc and stellar masses of 10^9─10^11 M_\ensuremath⊙, a purely stellar interpretation implies extreme central densities, \ensuremathρ_\ensuremath⋆ \ensuremath∼ 10^4─10^5 M_\ensuremath⊙ pc^\ensuremath-3 and in some cases up to \ensuremath∼10^9 M_\ensuremath⊙ pc^\ensuremath-3, far exceeding those of globular clusters. At such densities, the dynamical friction time for 10 M_\ensuremath⊙ stars in the central 0.1 pc is <0.1 Myr, driving rapid mass segregation. We investigate the dynamical consequences of such an environment using (i) a Fokker─Planck analysis of long-term core evolution, (ii) an analytical model for the collisional growth of a very massive star (VMS), and (iii) direct N-body simulations. All approaches show that runaway collisions produce a VMS with mass 9 \texttimes 10^3 < M_VMS [M_\ensuremath⊙] < 5 \texttimes 10^4 within <1 Myr. Once the supply of massive stars is depleted, the VMS contracts on a \ensuremath∼8000 yr Kelvin─Helmholtz timescale and undergoes a general relativistic collapse, leaving a massive black hole of mass M_\ensuremath∙ \ensuremath∼ 10^4 M_\ensuremath⊙. We conclude that LRDs are natural nurseries for the formation of heavy black hole seeds via stellar-dynamical processes. This pathway produces seed number densities that far exceed those expected from direct collapse models and, owing to the dense residual stellar core, can sustain high rates of tidal disruption events.

@article{2025ApJ...994...40P, author = {{Pacucci}, Fabio and {Hernquist}, Lars and {Fujii}, Michiko}, title = {{Little Red Dots are Nurseries of Massive Black Holes}}, journal = {\apj}, keywords = {Early universe, Galaxies, Galaxy dynamics, Galaxy evolution, Intermediate-mass black holes, N-body simulations, 435, 573, 591, 594, 816, 1083}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {40}, pages = {40}, doi = {10.3847/1538-4357/ae1619}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994...40P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, eprint = {2509.02664}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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Deciphering the Nature of Virgil: An Obscured Active Galactic Nucleus Lurking within an Apparently Normal Ly\ensuremathα Emitter during Cosmic Reionization

Pierluigi Rinaldi, Pablo G. Pérez-González, George H. Rieke, and 46 more authors

The Astrophysical Journal, Nov 2025

Abs DOI ADS arXiv

We present a comprehensive analysis of the MIRI Extremely Red Object Virgil, a Ly\ensuremathα emitter at z_spec = 6.6379 \ensuremath\pm 0.0035 with the photometric properties of a Little Red Dot. Leveraging new JWST/MIRI imaging from the MIDIS and PAHSPECS programs, we confirm Virgil’s extraordinary nature among galaxies in JADES/GOODS-South, exhibiting a strikingly red NIRCam-to-MIRI color (F444W─F1500W = 2.84 \ensuremath\pm 0.04 mag). Deep NIRSpec/PRISM spectroscopy from the OASIS program offers key insights into the host galaxy, revealing properties of an average star-forming galaxy during Cosmic Reionization, such as a subsolar metallicity, low-to-moderate dust content, and a relatively high ionization parameter and electron temperature. By estimating the star formation rate of Virgil from UV and H\ensuremathα, we find evidence that the galaxy is either entering or fading out of a bursty episode. Although line-ratio diagnostics employed at high z would classify Virgil as an active galactic nucleus (AGN), this classification becomes ambiguous once redshift evolution is considered. Nonetheless, Virgil occupies the same parameter space as recently confirmed AGNs at similar redshifts. The new deep MIRI data at 15 \ensuremathμm reinforce the AGN nature of Virgil, as inferred from multiple spectral energy distribution (SED) fitting codes. Virgil’s rising infrared SED and UV excess resemble those of Dust-Obscured Galaxies (DOGs) studied with Spitzer at Cosmic Noon, particularly blue-excess HotDOGs. Our results highlight the need for a multiwavelength approach incorporating MIRI to uncover such extreme sources at z \ensuremath≳ 6 and to shed light on the interplay between galaxy evolution and early black hole growth during Cosmic Reionization.

@article{2025ApJ...994...86R, author = {{Rinaldi}, Pierluigi and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Rieke}, George H. and {Lyu}, Jianwei and {D'Eugenio}, Francesco and {Wu}, Zihao and {Carniani}, Stefano and {Looser}, Tobias J. and {Shivaei}, Irene and {Boogaard}, Leindert A. and {Diaz-Santos}, Tanio and {Colina}, Luis and {{\"O}stlin}, G{\"o}ran and {Alberts}, Stacey and {{\'A}lvarez-M{\'a}rquez}, Javier and {Annuziatella}, Marianna and {Aravena}, Manuel and {Bhatawdekar}, Rachana and {Bunker}, Andrew J. and {Caputi}, Karina I. and {Charlot}, St{\'e}phane and {Crespo G{\'o}mez}, Alejandro and {Curti}, Mirko and {Eckart}, Andreas and {Gillman}, Steven and {Hainline}, Kevin and {Kumari}, Nimisha and {Hjorth}, Jens and {Iani}, Edoardo and {Inami}, Hanae and {Ji}, Zhiyuan and {Johnson}, Benjamin D. and {Jones}, Gareth C. and {Labiano}, {\'A}lvaro and {Maiolino}, Roberto and {Melinder}, Jens and {Moutard}, Thibaud and {Peissker}, Florian and {Rieke}, Marcia and {Robertson}, Brant and {Scholtz}, Jan and {Tacchella}, Sandro and {van der Werf}, Paul P. and {Walter}, Fabian and {Williams}, Christina C. and {Willott}, Chris and {Witstok}, Joris and {{\"U}bler}, Hannah and {Zhu}, Yongda}, title = {{Deciphering the Nature of Virgil: An Obscured Active Galactic Nucleus Lurking within an Apparently Normal Ly{\ensuremath{\alpha}} Emitter during Cosmic Reionization}}, journal = {\apj}, keywords = {Active galactic nuclei, High-redshift galaxies, Galaxy evolution, Near infrared astronomy, AGN host galaxies, Galaxy formation, Photoionization, Spectral energy distribution, Infrared astronomy, Galaxies, Infrared photometry, 16, 734, 594, 1093, 2017, 595, 2060, 2129, 786, 573, 792}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {86}, pages = {86}, doi = {10.3847/1538-4357/ae089c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994...86R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, sed, spectroscopy}, eprint = {2504.01852}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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A little red dot at z = 7.3 within a large galaxy overdensity

Jan-Torge Schindler, Joseph F. Hennawi, Frederick B. Davies, and 11 more authors

Nature Astronomy, Nov 2025

Abs DOI ADS arXiv

The nature of ‘little red dots’ and their relation to other forms of accreting supermassive black holes remain an open question. Here we report the discovery of a little red dot at z = 7.3. It is attenuated by moderate amounts of dust, A_V = 2.79 mag, and has an intrinsic bolometric luminosity of 10^46.6 erg s^-1 and a supermassive black hole mass of 5 \texttimes 10^8 M_☉. Most notably, this object is embedded in an overdensity of eight nearby galaxies, allowing us to calculate a spectroscopic estimate of the clustering of galaxies around little red dots. We find a little red dot versus galaxy cross- correlation length of r_0 = 8 \ensuremath\pm 2 h^-1 cMpc, comparable to that of z \ensuremath≈ 6 ultraviolet-luminous quasars. The resulting estimate of their minimum dark matter halo mass log_10(M_halo ,min/M_☉ ) =12 .0_-1.0^+0.8 indicates that nearly all haloes above this mass must host actively accreting supermassive black holes at z \ensuremath≈ 7, in strong contrast with the far smaller duty cycle of luminous quasars (<1%). Our results, taken at face value, motivate a picture in which supermassive black holes in little red dot phases could serve as the obscured precursors of ultraviolet-luminous quasars, which provides a natural explanation for the short ultraviolet-luminous lifetimes inferred from both quasar clustering and quasar proximity zones.

@article{2025NatAs...9.1732S, author = {{Schindler}, Jan-Torge and {Hennawi}, Joseph F. and {Davies}, Frederick B. and {Bosman}, Sarah E. I. and {Endsley}, Ryan and {Wang}, Feige and {Yang}, Jinyi and {Barth}, Aaron J. and {Eilers}, Anna-Christina and {Fan}, Xiaohui and {Kakiichi}, Koki and {Maseda}, Michael and {Pizzati}, Elia and {Nanni}, Riccardo}, title = {{A little red dot at z = 7.3 within a large galaxy overdensity}}, journal = {Nature Astronomy}, year = {2025}, month = nov, volume = {9}, pages = {1732-1744}, doi = {10.1038/s41550-025-02660-1}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NatAs...9.1732S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, clustering, dust, early universe, spectroscopy}, eprint = {2411.11534}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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A Deep Dive down the Broad-line Region: Permitted O I, Ca II, and Fe II Emission in an Active Galactic Nucleus Little Red Dot at z = 5.3

Roberta Tripodi, Maruša Bradač, Francesco D’Eugenio, and 27 more authors

The Astrophysical Journal Letters, Nov 2025

Abs DOI ADS arXiv

We present a spectroscopic analysis of a broad-line active galactic nucleus (AGN) selected as a little red dot (LRD) at z = 5.3 behind the Bullet cluster (Bz5.3) based on JWST/NIRCam and NIRSpec data. The detection of strong Fe II, O I, and Ca II triplet emission lines, along with the evidence of broad Balmer lines, provides strong evidence of a broad-line region (BLR) and an accreting supermassive black hole. Notably, we report the first detection of the \ensuremathλ1304 bump (i.e., a blend of O I \ensuremathλ1304 and Si II) at high redshift, a feature commonly seen in local AGNs but not yet reported in the early Universe. The O I \ensuremathλ1304/\ensuremathλ8446 photon ratio provides an independent measurement of dust attenuation in galaxies. In Bz5.3, this ratio is highly suppressed (0.1─0.3), implying significant internal dust extinction, with estimated dust attenuation A_V \ensuremath∼ 0.4─1.0. We identify Ly\ensuremathβ fluorescence as the dominant excitation mechanism of the low-ionization lines, with additional contributions from collisional excitation. High O I \ensuremathλ8446 equivalent width and weak O I \ensuremathλ7774 support this interpretation. The detection of iron emission, whether from broad permitted or narrow forbidden lines, supports the presence of a stratified BLR, as also recently proposed in local LRDs. Photoionization modeling of O I \ensuremathλ8446 and Ca II further suggests the coexistence of multiple gas phases with distinct densities and ionization states, highlighting the complexity of the BLR. Bz5.3 thus offers a rare window into early AGN activity and BLR physics at early times.

@article{2025ApJ...994L...6T, author = {{Tripodi}, Roberta and {Brada{\v{c}}}, Maru{\v{s}}a and {D'Eugenio}, Francesco and {Martis}, Nicholas and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Willott}, Chris and {Pentericci}, Laura and {Moreschini}, Bianca and {Markevitch}, Maxim and {Asada}, Yoshihisa and {Calabr{\'o}}, Antonello and {Desprez}, Guillaume and {Felicioni}, Giordano and {Gaspar}, Gaia and {Gonzalez}, Anthony H. and {Harshan}, Anishya and {Ji}, Xihan and {Jude{\v{z}}}, Jon and {Lemaux}, Brian C. and {Marconi}, Alessandro and {Markov}, Vladan and {Merida}, Rosa M. and {Napolitano}, Lorenzo and {Noirot}, Ga{\"e}l and {Parente}, Massimiliano and {Peter}, Annika H. G. and {Robbins}, Luke and {Robertson}, Andrew and {Sarrouh}, Ghassan T. E. and {Sawicki}, Marcin}, title = {{A Deep Dive down the Broad-line Region: Permitted O I, Ca II, and Fe II Emission in an Active Galactic Nucleus Little Red Dot at z = 5.3}}, journal = {\apjl}, keywords = {Astrophysical black holes, AGN host galaxies, Galaxy spectroscopy, 98, 2017, 2171}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {L6}, pages = {L6}, doi = {10.3847/2041-8213/ae13a9}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994L...6T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, early universe, emission lines, jwst, spectroscopy}, eprint = {2507.20684}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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Extreme properties of a compact and massive accreting black hole host in the first 500 Myr

Roberta Tripodi, Nicholas Martis, Vladan Markov, and 29 more authors

Nature Communications, Nov 2025

Abs DOI ADS arXiv

Little red dots (LRDs) are a high redshift galaxy population. Despite their high number densities, their nature is still uncertain. Here we present CANUCS-LRD-z8.6, a spectroscopically confirmed little red dot at a spectroscopic redshift of z_spec = 8.6319, hosting an active galactic nucleus. Its spectrum exhibits broad H\ensuremathβ\ensuremathλ4863 Å emission, high-ionization lines (C iv, N iv]), high electron temperature, which are indicative of active galactic nucleus activity, and low metallicity (Z < 0.1\ensuremath-0.2Z_\ensuremath⊙). The inferred black hole mass, MBH=1.0\ensuremath-0.4+0.6\texttimes108M \ensuremath⊙, poses strong constraints on current black hole formation models and simulations. Additionally, its black hole is over-massive relative to its host, deviating from local M_BH \ensuremath- M_* relations, suggesting an early, rapid black hole growth preceding that of its galaxy. CANUCS-LRD-z8.6 may represent an evolutionary link between early massive black holes and the luminous quasars observed at z = 6.

@article{2025NatCo..16.9830T, author = {{Tripodi}, Roberta and {Martis}, Nicholas and {Markov}, Vladan and {Brada{\v{c}}}, Maru{\v{s}}a and {Di Mascia}, Fabio and {Cammelli}, Vieri and {D'Eugenio}, Francesco and {Willott}, Chris and {Curti}, Mirko and {Bhatt}, Maulik and {Gallerani}, Simona and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Singh}, Jasbir and {Gaspar}, Gaia and {Harshan}, Anishya and {Jude{\v{z}}}, Jon and {Merida}, Rosa M. and {Desprez}, Guillaume and {Sawicki}, Marcin and {Goovaerts}, Ilias and {Muzzin}, Adam and {Noirot}, Ga{\"e}l and {Sarrouh}, Ghassan T. E. and {Abraham}, Roberto and {Asada}, Yoshihisa and {Brammer}, Gabriel and {Estrada-Carpenter}, Vicente and {Felicioni}, Giordano and {Fujimoto}, Seiji and {Iyer}, Kartheik and {Mowla}, Lamiya and {Strait}, Victoria}, title = {{Extreme properties of a compact and massive accreting black hole host in the first 500 Myr}}, journal = {Nature Communications}, keywords = {Physical Sciences, Astronomical and Space Sciences}, year = {2025}, month = nov, volume = {16}, number = {1}, eid = {9830}, pages = {9830}, doi = {10.1038/s41467-025-65070-x}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NatCo..16.9830T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, host galaxy, spectroscopy}, eprint = {2412.04983}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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Luminous mid-IR selected obscured quasars at cosmic noon in SDSS Stripe82 II: spectroscopic diversity and broad H \ensuremathα emissions

Ben Wang, Yuzo Ishikawa, Joseph F. Hennawi, and 5 more authors

Monthly Notices of the Royal Astronomical Society, Nov 2025

Abs DOI ADS arXiv

We present a multiwavelength spectroscopic survey of 23 luminous mid- infrared-selected Type-2 quasars at the redshifts of ─3.49. The targets were selected in the SDSS Stripe 82 field based on their bright WISE 22 m detections and extremely faint or red optical counterparts. Near-infrared (Gemini/Gemini Near-InfraRed Spectrograph) and optical (Keck/Low Resolution Imaging Spectrometer and Keck Cosmic Web Imager Integral Field Spectrograph) spectroscopy confirm 23 out of 24 candidates as Type-2 quasars, including 12 objects at . The spectra exhibit strong rest-frame UV and optical emission lines (Ly , C IV, [O III], H ) with a wide range of line widths, indicating significant spectral diversity. Approximately one-third of the sample (8 of 23) shows broad H emission (full width at half- maximum, FWHM km s) despite their Type-2 classification, while the rest have only narrow lines (FWHM km s) characteristic of classical obscured quasars. Notably, these broad-line Type-2 quasars share similar spectral energy distributions with the James Webb Space Telescope (JWST)-discovered ’little red dot’, suggesting that our sample could be lower redshift analogues of the heavily obscured broad-line AGNs uncovered by JWST. We also find that the [O III] 5007 emission is relatively weak for their high-bolometric luminosities, deviating from trends seen in lower-z Type-2 quasi-stellar objects (QSOs). A new composite spectrum for Type-2 QSOs is built using our sample. Overall, our results demonstrate that mid-infrared selection efficiently uncovers diverse populations of obscured quasars and that spectroscopic follow-up is crucial for revealing their true nature. This study provides new insights into heavily obscured supermassive black hole growth at cosmic noon and bridges the gap to the obscured active galactic nuclei populations being revealed by JWST.

@article{2025MNRAS.544..687W, author = {{Wang}, Ben and {Ishikawa}, Yuzo and {Hennawi}, Joseph F. and {Cai}, Zheng and {Richards}, Gordon T. and {Zakamska}, Nadia L. and {Yang}, Daming and {Schindler}, Jan-Torge}, title = {{Luminous mid-IR selected obscured quasars at cosmic noon in SDSS Stripe82 II: spectroscopic diversity and broad H {\ensuremath{\alpha}} emissions}}, journal = {\mnras}, keywords = {galaxies: high-redshift, quasars: emission lines, quasars: general, quasars: supermassive black holes, infrared: galaxies}, year = {2025}, month = nov, volume = {544}, number = {1}, pages = {687-707}, doi = {10.1093/mnras/staf1730}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.544..687W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, multi-wavelength, non-jwst, spectroscopy}, eprint = {2508.02792}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {11} }

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Little red dots as embryos of active galactic nuclei

Jian-Min Wang, Yi-Lin Wang, Yong-Jie Chen, and 7 more authors

arXiv e-prints, Nov 2025

Abs ADS arXiv

As an unprecedented large population in the early universe, the JWST- discovered little red dots (LRDs) have garnered much attention for formation of massive black holes and galaxies, but their nature remains a mystery. The LRDs appearing as “Chimeras” like both active galactic nuclei (AGNs) and galaxies have stimulated renewed interest in the roadmap of central massive black hole (cMBH) formation in AGNs. In this paper, we suggest that the LRDs contain M_∙≲10^6 M_⊙ cMBHs as demonstrated by the Sołtan argument and there is a large population of stellar-mass black holes (sMBHs with total mass of \mathscrM_m_∙) embedded inside cMBH accretion disks (cMBH-disk) as motivated by anomalous reverberations of broad Hβ line in local AGNs. This embryo structure of LRDs (M_∙<\mathscrM_m_∙) is formed as a consequence of gravitational collapse of primordial clouds. In this Chimera, accretion onto sMBHs powers the rest- frame optical continuum of the LRDs but the UV continuum is jointly contributed by slim parts of the cMBH-disks and nuclear starbursts in the core of collapsing clouds governing the appearance of the observed V-shaped spectral energy distributions (SEDs). Outflowing clumped-envelopes are unavoidably formed by radiation pressure leading to absorption features of the Balmer lines. The present model works very well for LRDs’ SEDs and avoids the issues of overly massive cMBHs. Evolution of LRDs is briefly discussed including gravitational waves.

@article{2025arXiv251109278W, author = {{Wang}, Jian-Min and {Wang}, Yi-Lin and {Chen}, Yong-Jie and {Liu}, Jun-Rong and {Songsheng}, Yu-Yang and {Cheng}, Cheng and {Li}, Yan-Rong and {Du}, Pu and {Zhang}, Hao and {Zhao}, Yu}, title = {{Little red dots as embryos of active galactic nuclei}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.09278}, pages = {arXiv:2511.09278}, archiveprefix = {arXiv}, eprint = {2511.09278}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251109278W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, sed, theory}, month_numeric = {11} }

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Little Red Dots host Black Hole Stars: A unified family of gas-reddened AGN revealed by JWST/NIRSpec spectroscopy

Anna de Graaff, Raphael E. Hviding, Rohan P. Naidu, and 34 more authors

arXiv e-prints, Nov 2025

Abs ADS arXiv

We use the DAWN JWST Archive to construct and characterise a sample of 116 little red dots (LRDs) across 2.3<z<9.3, selecting all sources with v-shaped UV-optical continua from NIRSpec/PRISM spectra and compact morphologies in NIRCam/F444W imaging. We show that LRD continuum spectra are ubiquitously well described by modified blackbodies across \raisebox-0.5ex\textasciitilde0.4-1.0μm, with typical T\raisebox-0.5ex\textasciitilde5000K or λ_peak\raisebox-0.5ex\textasciitilde0.65μm across 2 dex in luminosity, and a tail toward T\raisebox-0.5ex\textasciitilde2000K. LRDs therefore trace a locus in the Hertzsprung-Russell diagram that is directly analogous to stars on the Hayashi track, strongly supporting the picture that LRDs are AGN embedded in thermalised dense gas envelopes in approximate hydrostatic equilibrium. Hotter LRDs with λ_peak<0.65μm typically have strong Balmer breaks, redder UV slopes and high optical luminosities; other LRDs show weak or no Balmer breaks, and wide variety in β_UV and L_5100. Crucially, we demonstrate that the UV-optical continuum shapes and luminosities are strongly linked to the Hα, Hβ, [OIII] and OI line properties. There is a tight linear relation between the Hα and optical continuum luminosities, as well as Hα and OI_8446, indicating that Balmer, OI and optical emission must primarily be powered by the same source. The Balmer decrement increases strongly toward higher L_Hα, L_5100 and Balmer break strength, providing key evidence for luminosity-dependent effects of collisional (de-)excitation and resonant scattering in the gaseous envelopes. In contrast, we show that [OIII] emission likely originates from star-forming host galaxies, and that its strong correlation with Balmer break strength arises naturally from variation in the AGN-to-host ratio. Our work presents an empirical description of the nature and structure of LRDs, defining a new benchmark for ongoing LRD model developments.

@article{2025arXiv251121820D, author = {{de Graaff}, Anna and {Hviding}, Raphael E. and {Naidu}, Rohan P. and {Greene}, Jenny E. and {Miller}, Tim B. and {Leja}, Joel and {Matthee}, Jorryt and {Brammer}, Gabriel and {Katz}, Harley and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Bose}, Sownak and {Chisholm}, John and {Cleri}, Nikko J. and {Dayal}, Pratika and {Feldmann}, Robert and {Fudamoto}, Yoshinobu and {Fujimoto}, Seiji and {Furtak}, Lukas J. and {Glazebrook}, Karl and {Gottumukkala}, Rashmi and {Heintz}, Kasper E. and {Kokorev}, Vasily and {Labbe}, Ivo and {Maseda}, Michael V. and {McConachie}, Ian and {Nanayakkara}, Themiya and {Nelson}, Erica and {Nowaczyk}, Przemys{\l}aw and {Oesch}, Pascal A. and {Rix}, Hans-Walter and {Setton}, David J. and {Torralba}, Alberto and {Walter}, Fabian and {Wang}, Bingjie and {Weibel}, Andrea and {van der Wel}, Arjen}, title = {{Little Red Dots host Black Hole Stars: A unified family of gas-reddened AGN revealed by JWST/NIRSpec spectroscopy}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.21820}, pages = {arXiv:2511.21820}, archiveprefix = {arXiv}, eprint = {2511.21820}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251121820D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, morphology, sed, spectroscopy}, month_numeric = {11} }

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Investigating Little Red Dots with UV Excess: Are They the High-redshift Siblings of Blue Hot Dust-obscured Galaxies?

Lulu Bao, Chao-Wei Tsai, Jingwen Wu, and 7 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS arXiv

Little red dots (LRDs), newly identified compact and dusty galaxies with an unexpectedly high number density observed by JWST, have an unusual “V-shaped” rest-frame UV to near-infrared spectral energy distribution (SED). A group of hyperluminous, obscured quasars with excess blue emission, called blue-excess hot dust- obscured galaxies (BHDs), also exhibit qualitatively similar SEDs to those of LRDs. They represent a rare population of galaxies hosting supermassive black holes (SMBHs) accreting near the Eddington limit at redshifts z \ensuremath∼ 1–4. In this study, we compare their multiwavelength SEDs to investigate whether LRDs, or a subset of them, could be high-redshift analogs of BHDs. Our analysis reveals that despite their similar “V-shape” SEDs, LRDs appear to be a different population than BHDs. The “V-shape” of BHDs appears at longer wavelengths compared to LRDs due to different selection strategies, suggesting LRDs have much less dust attenuation than typical BHDs. The bluer colors in the rest-frame infrared (continuum) emission of LRDs suggest the absence of hot dust heated by active galactic nuclei (AGN) accretion activities. We also argue that the blue excess in LRDs is unlikely from AGN scattered light. The compact morphologies and lower X-ray detection frequencies of LRDs suggest a distinct formation pathway from BHDs, which are thought to be powered by super- Eddington accretion onto central SMBHs following major galaxy mergers.

@article{2025ApJ...992..117B, author = {{Bao}, Lulu and {Tsai}, Chao-Wei and {Wu}, Jingwen and {Wang}, Tao and {Li}, Guodong and {Assef}, Roberto J. and {Diaz-Santos}, Tanio and {Eisenhardt}, Peter R. M. and {Stern}, Daniel and {Blain}, Andrew W.}, title = {{Investigating Little Red Dots with UV Excess: Are They the High-redshift Siblings of Blue Hot Dust-obscured Galaxies?}}, journal = {\apj}, keywords = {Infrared galaxies, Active galactic nuclei, High-redshift galaxies, Active galaxies, AGN host galaxies, 790, 16, 734, 17, 2017}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {117}, pages = {117}, doi = {10.3847/1538-4357/ae019e}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992..117B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, multi-wavelength, non-agn, sed}, eprint = {2508.21678}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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Seeding Cores: A Pathway for Nuclear Star Clusters from Bound Star Clusters in the First Billion Years

Fred Angelo Batan Garcia, Massimo Ricotti, and Kazuyuki Sugimura

The Open Journal of Astrophysics, Oct 2025

Abs DOI ADS arXiv

We model the formation of star clusters in a dwarf galaxy progenitor during the first 700 Myr of cosmic history using a cosmological radiation-hydrodynamic simulation with a sub-grid star formation efficiency (SFE) model calibrated from AU-scale radiation-MHD simulations of molecular clouds with varying mass, density, and metallicity. In comparison to a constant SFE model, our model yields more bursty star formation, a more abundant massive star cluster population, and overall a higher stellar mass. Clouds reach SFEs up to 80%, forming bound star clusters (densities , radii ) resembling those observed by the James Webb Space Telescope (JWST) in strongly lensed galaxies. Star clusters follow a flat power-law mass function with slope \ensuremathΓ\ensuremath∼\ensuremath-0.4. The most massive star clusters () grow through mergers and have metallicity spreads of 0.05\ensuremath-0.1 dex that roughly scale with mass. The second burst of star formation produce loosely bound star clusters with higher metallicities: at lower SFEs (2 - 20%). At z\ensuremath∼8.7, a nuclear star cluster (NSC) is seeded, growing 83% of its mass (, 20% of the galaxy’s stellar mass) through mergers with pre-existing clusters and the rest through in-situ star formation. The early formation of NSCs has interesting implications for seeding supermassive black holes and the population of little red dots recently discovered by JWST at z\ensuremath≳5.

@article{2025OJAp....8E.146G, author = {{Garcia}, Fred Angelo Batan and {Ricotti}, Massimo and {Sugimura}, Kazuyuki}, title = {{Seeding Cores: A Pathway for Nuclear Star Clusters from Bound Star Clusters in the First Billion Years}}, journal = {The Open Journal of Astrophysics}, year = {2025}, month = oct, volume = {8}, eid = {146}, pages = {146}, doi = {10.33232/001c.145064}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025OJAp....8E.146G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {175145281}, lrdkeys = {black hole mass, early universe, jwst, simulation, starburst}, eprint = {2503.08779}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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RUBIES: A spectroscopic census of little red dots: All point sources with v-shaped continua have broad lines

Raphael E. Hviding, Anna de Graaff, Tim B. Miller, and 16 more authors

Astronomy & Astrophysics, Oct 2025

Abs DOI ADS arXiv

The physical nature of little red dots (LRDs), a population of compact red galaxies revealed by JWST, remains unclear. Photometric samples were constructed from varying selection criteria with limited spectroscopic follow-up available to test intrinsic spectral shapes and the prevalence of broad emission lines. We used the RUBIES survey, a large spectroscopic program with wide color-morphology coverage and homogeneous data quality, to systematically analyze the emission-line kinematics, spectral shapes, and morphologies of \ensuremath∼1500 galaxies at z > 3.1. We identified broad Balmer lines via a novel fitting approach that simultaneously models NIRSpec/PRISM and G395M spectra, yielding 80 broad-line sources with 28 (35%) at z > 6. A large subpopulation naturally emerged from the broad Balmer line sources, with 36 exhibiting v-shaped UV-to-optical continua and a dominant point source component in the rest-optical; we define these as spectroscopic LRDs, constituting the largest such sample to date. Strikingly, the spectroscopic LRD population is largely recovered when either a broad line or rest-optical point source is required in combination with a v-shaped continuum, suggesting an inherent link between these three defining characteristics. We compared the spectroscopic LRD sample to published photometric searches. Although these selections have high accuracy, 80%‑95% down to F444W < 26.5, only 50%‑80% of the RUBIES LRDs were photometrically identified, depending on the selection criteria used. The remainder were missed due to a mixture of faint rest-UV photometry, comparatively blue rest-optical colors, or highly uncertain photometric redshifts. Our findings highlight that well-selected spectroscopic campaigns are essential for robust LRD identification, while photometric criteria require refinement to capture the full population.

@article{2025A&A...702A..57H, author = {{Hviding}, Raphael E. and {de Graaff}, Anna and {Miller}, Tim B. and {Setton}, David J. and {Greene}, Jenny E. and {Labb{\'e}}, Ivo and {Brammer}, Gabriel and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Cleri}, Nikko J. and {Leja}, Joel and {Maseda}, Michael V. and {McConachie}, Ian and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Oesch}, Pascal A. and {Wang}, Bingjie and {Whitaker}, Katherine E. and {Williams}, Christina C.}, title = {{RUBIES: A spectroscopic census of little red dots: All point sources with v-shaped continua have broad lines}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift}, year = {2025}, month = oct, volume = {702}, eid = {A57}, pages = {A57}, doi = {10.1051/0004-6361/202555816}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...702A..57H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {177925174}, lrdkeys = {emission lines, jwst, sample selection, sed, spectroscopy}, eprint = {2506.05459}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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The M_\rm BH-M_* Relationship at 3<z<7: Big Black Holes in Little Red Dots

Brenda L. Jones, Dale D. Kocevski, Fabio Pacucci, and 25 more authors

arXiv e-prints, Oct 2025

Abs ADS arXiv

JWST has identified a large population of faint, broad-line active galactic nuclei (AGN) in the early universe that are powered by black holes (BHs) that often appear overmassive relative to their host galaxies. In this study, we examine the relationship between BH mass and galaxy stellar mass at 33σ above the relationship measured for local broad-line AGN. We derive an intrinsic scatter in this relationship of 0.9 dex, which does not vary over the redshift range of our sample. We also find that the M_\rm BH/M_⋆ ratio increases by 2.3 dex from z = 3.5 and z = 6.5 with a confidence level of > 3σ. We attribute this trend with the increasing fraction of LRDs in our sample at z>4 as their host masses are \sim1 dex lower than the non-LRD AGN in our sample. These results support a picture in which the BHs powering JWST’s broad-line AGN are genuinely overmassive and become increasingly so with redshift. We discuss the implications of our findings on early BH growth relative to that of their host galaxies and the constraints it places on BH seeding models.

@article{2025arXiv251007376J, author = {{Jones}, Brenda L. and {Kocevski}, Dale D. and {Pacucci}, Fabio and {Taylor}, Anthony J. and {Finkelstein}, Steven L. and {Buchner}, Johannes and {Trump}, Jonathan R. and {Somerville}, Rachel S. and {Hirschmann}, Michaela and {Yung}, L. Y. Aaron and {Barro}, Guillermo and {Bell}, Eric F. and {Bisigello}, Laura and {Calabro}, Antonello and {Cleri}, Nikko J. and {Dekel}, Avishai and {Dickinson}, Mark and {Gandolfi}, Giovanni and {Giavalisco}, Mauro and {Grogin}, Norman A. and {Inayoshi}, Kohei and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Napolitano}, Lorenzo and {Onoue}, Masafusa and {Ravindranath}, Swara and {Rodighiero}, Giulia and {Wilkins}, Stephen M.}, title = {{The $M\_{\rm BH}-M\_{*}$ Relationship at $3<z<7$: Big Black Holes in Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.07376}, pages = {arXiv:2510.07376}, archiveprefix = {arXiv}, eprint = {2510.07376}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251007376J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, spectroscopy}, month_numeric = {10} }

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The BlueDOG at Cosmic Noon: A Possible Analog to Little Red Dots?

Seongjae Kim, Woong-Seob Jeong, Minjin Kim, and 3 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS arXiv

We discovered a hyperluminous dust-obscured galaxy with mysterious blue- excess emission (BlueDOG) in the rest-frame UV of its spectral energy distribution (SED) from a multiwavelength survey in the AKARI Deep Field - South (ADF-S). We present the results of SED analysis with multiwavelength photometric data and spectroscopic analysis, observed with Gemini-S/GMOS, FLAMINGOS-2, to explore the origin of blue-excess emission of a hyperluminous BlueDOG, ADFS-KMTDOG-102, at z = 2.6. The SED analysis shows that this BlueDOG is a highly massive system (log M_*/M_\ensuremath⊙ = 12.3) with substantial extinction. Additionally, the proportion of the old stellar population exceeds that of the young stellar population, which suggests stellar evolution cumulated from the early Universe. The mass of the supermassive black hole estimated using the extinction-corrected broad H\ensuremathα emission line yields log M_BH/M_\ensuremath⊙ = 10.2. We discuss the similarity between the BlueDOG and “Little Red Dots” (LRDs), recently discovered with the James Webb Space Telescope, showing SED shapes remarkably similar to those of LRDs. The UV emission line ratios indicate that the emission lines are primarily powered by the central active galactic nuclei (AGN). In contrast, the origin of the blue-excess UV continuum remains ambiguous, since both recent star formation and AGN-induced scattered light are viable explanations, based on the results from the SED fitting and scattered light modeling.

@article{2025ApJ...992...70K, author = {{Kim}, Seongjae and {Jeong}, Woong-Seob and {Kim}, Minjin and {Jun}, Hyunsung D. and {Yang}, Yujin and {Nakagawa}, Takao}, title = {{The BlueDOG at Cosmic Noon: A Possible Analog to Little Red Dots?}}, journal = {\apj}, keywords = {Active galaxies, High-redshift galaxies, Infrared galaxies, Supermassive black holes, 17, 734, 790, 1663}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {70}, pages = {70}, doi = {10.3847/1538-4357/adff59}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992...70K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, emission lines, sed, spectroscopy}, eprint = {2508.19618}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging

Gene C. K. Leung, Steven L. Finkelstein, Pablo G. Pérez-González, and 20 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS arXiv

JWST has revealed a large population of compact, red objects at z > 4 known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 88 LRDs from the JWST PRIMER survey with complete photometric coverage from 1 to 18 \ensuremathμm using NIRCam and MIRI imaging, representing the most extensive SED analysis on a large LRD sample with long-wavelength MIRI data. We examine SED models in which either galaxy or active galactic nucleus (AGN) emission dominates the rest-frame UV or optical continuum, extracting physical properties to explore each scenario’s implications. In the galaxy-only model, we find massive, dusty stellar populations alongside unobscured, low- mass components, hinting at inhomogeneous obscuration. The AGN- only model indicates dusty, luminous AGNs with low hot dust fractions compared to typical quasars. A hybrid AGN and galaxy model suggests low-mass, unobscured galaxies in the UV, with stellar mass estimates spanning \ensuremath∼2 dex across the different models, underscoring the need for caution in interpreting LRD stellar masses. With MIRI photometry, the galaxy-only model produces stellar masses within cosmological limits, but extremely high stellar mass densities are inferred. The hybrid model infers highly overmassive black holes exceeding those in recently reported high-redshift AGNs, hinting at a partial AGN contribution to the rest-optical continuum or widespread super-Eddington accretion. Our findings highlight the extreme conditions required for both AGN- and galaxy-dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.

@article{2025ApJ...992...26L, author = {{Leung}, Gene C. K. and {Finkelstein}, Steven L. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Morales}, Alexa M. and {Taylor}, Anthony J. and {Barro}, Guillermo and {Kocevski}, Dale D. and {Akins}, Hollis B. and {Carnall}, Adam C. and {Ch{\'a}vez Ortiz}, {\'O}scar A. and {Cleri}, Nikko J. and {Cullen}, Fergus and {Donnan}, Callum T. and {Dunlop}, James S. and {Ellis}, Richard S. and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Lucas}, Ray A. and {McLeod}, Derek J. and {Papovich}, Casey and {Yung}, L. Y. Aaron}, title = {{Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging}}, journal = {\apj}, keywords = {Active galactic nuclei, Galaxy formation, High-redshift galaxies, Supermassive black holes, 16, 595, 734, 1663}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {26}, pages = {26}, doi = {10.3847/1538-4357/adfcce}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992...26L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, non-agn, photometry, sed}, eprint = {2411.12005}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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A big red dot at cosmic noon

Federica Loiacono, Roberto Gilli, Marco Mignoli, and 22 more authors

Astronomy & Astrophysics, Oct 2025

Abs DOI ADS arXiv

We report the discovery of a little red dot (LRD), dubbed BiRD (’big red dot’), at z \ensuremath∼ 2.33 in the field around the z \ensuremath∼ 6.3 quasar SDSS J1030+0524. Using JWST/NIRCam images, we identified it as a bright outlier in the F200W \ensuremath- F356W color versus F356W magnitude diagram of point sources in the field. The NIRCam/WFSS spectrum reveals the emission from He I\ensuremathλ 10830 and Pa\ensuremathγ line, both displaying a narrow and a broad (FWHM \ensuremath≳ 2000 km s^\ensuremath-1) component. The He I line is affected by an absorption feature, tracing dense gas with He I column density in the 2^3S level N(He I) \ensuremath∼ 0.5 \ensuremath- 1.2 \texttimes 10^14 cm^\ensuremath-2, depending on the location of the absorber, which is outflowing at a speed of \ensuremath∆ v = \ensuremath- 830 \ensuremath- 148 + 131 km s^\ensuremath-1. As observed in the majority of LRDs, BiRD does not exhibit any X-ray or radio emission down to 3.7 \texttimes 10^42 erg s^\ensuremath-1 and 3 \texttimes 10^39 erg s^\ensuremath-1, respectively. The black hole mass and the bolometric luminosity, both inferred from the Pa\ensuremathγ broad component, amount to M_BH \ensuremath∼ 10^8 M_\ensuremath⊙ and L_bol \ensuremath∼ 3 \texttimes 10^45 erg s^\ensuremath-1, respectively. Intriguingly, BiRD presents strict analogies with other two LRDs spectroscopically confirmed at cosmic noon, namely, GN-28074 (nicknamed Rosetta Stone) at z \ensuremath∼ 2.26 and RUBIES-BLAGN-1 at z \ensuremath∼ 3.1. The blueshifted He I absorption detected for all three sources suggests that gas outflows could be common in LRDs. We derived a first estimate of the space density of LRDs at z \ensuremath∼ 2 \ensuremath- 3 based on JWST data, as a function of the bolometric luminosity and black hole mass. The space density \ensuremathΦ ( L ) = 4 . 0 \ensuremath- 2.4 + 4.0 \texttimes 10 \ensuremath- 6 Mpc^\ensuremath-3 dex^\ensuremath-1 is only a factor of \ensuremath∼2 \ensuremath- 3 lower than that of UV- selected quasars with comparable bolometric luminosity and redshift, meaning that the contribution of LRDs to the broader AGN population is also relevant at cosmic noon. A similar trend has also been observed with respect to black hole masses. As suggested by recent theories, if LRDs can indeed serves as probes of the very first and rapid growth of black hole seeds, our finding suggests that the formation of black hole seeds continues to be efficient at least up to cosmic noon.

@article{2025A&A...703A..36L, author = {{Loiacono}, Federica and {Gilli}, Roberto and {Mignoli}, Marco and {Mazzolari}, Giovanni and {Decarli}, Roberto and {Brusa}, Marcella and {Calura}, Francesco and {Chiaberge}, Marco and {Comastri}, Andrea and {D'Amato}, Quirino and {Iwasawa}, Kazushi and {Juod{\v{z}}balis}, Ignas and {Lanzuisi}, Giorgio and {Maiolino}, Roberto and {Marchesi}, Stefano and {Norman}, Colin and {Peca}, Alessandro and {Prandoni}, Isabella and {Sapori}, Matteo and {Signorini}, Matilde and {Tozzi}, Paolo and {Vanzella}, Eros and {Vignali}, Cristian and {Vito}, Fabio and {Zamorani}, Gianni}, title = {{A big red dot at cosmic noon}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift, quasars: absorption lines, quasars: supermassive black holes}, year = {2025}, month = oct, volume = {703}, eid = {A36}, pages = {A36}, doi = {10.1051/0004-6361/202555946}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...703A..36L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {178133386}, lrdkeys = {black hole mass, emission lines, jwst, multi-wavelength, spectroscopy}, eprint = {2506.12141}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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Modeling the “Dark-matter Dominated” Dwarf Galaxy Segue 1 with a Supermassive Black Hole

Nathaniel Lujan, Karl Gebhardt, Richard Anantua, and 11 more authors

The Astrophysical Journal Letters, Oct 2025

Abs DOI ADS

The dwarf spheroidal galaxy, Segue 1, is thought to have one of the largest ratios of dark matter to stellar mass. Using orbit-based dynamical models, we model Segue 1, including a dark halo and a central black hole. The best-fit model requires a black hole mass of 4.5 \ensuremath\pm 1.5 \texttimes 10^5 M_\ensuremath⊙. The value of the black hole mass is similar either with or without a dark halo. The mass-to-light ratio of the stars is poorly constrained by the dynamical modeling, reflecting that Segue 1 is dominated by mass other than stars. Dynamical models that exclude a black hole provide a worse fit and require a dark halo with very-small-scale radii of below 100 pc. Additionally, the zero black hole models require a stellar orbital distribution that is highly radially biased. The model with a black hole provides an orbital structure that is close to isotropic, more similar to other well-studied systems. We argue that the two-parameter models of stars and black hole provide a better description of Segue 1 than the three-parameter models of stars and two dark halo components. Additional support for a central black hole comes from a significant increase in the central rotation. Using individual velocities, we measure a rotation amplitude of 9.0 \ensuremath\pm 2.4 km s^‑1. Segue 1 is likely being tidally stripped at large radii, and we might be witnessing the remnant nucleus of a more massive system. Alternatively, given the high black hole mass relative to the stellar mass, Segue 1 is analogous to the Little Red Dots seen in the early Universe.

@article{2025ApJ...992L..25L, author = {{Lujan}, Nathaniel and {Gebhardt}, Karl and {Anantua}, Richard and {Chase}, Owen and {Debski}, Maya H. and {Finley}, Claire and {Gomez}, Loraine V. and {Gupta}, Om and {Lawson}, Alex J. and {Marron}, Izabella and {Martinez}, Zorayda and {Painter}, Connor A. and {Sklansky}, Yonatan and {West}, Hayley}, title = {{Modeling the ``Dark-matter Dominated'' Dwarf Galaxy Segue 1 with a Supermassive Black Hole}}, journal = {\apjl}, keywords = {Black holes, 162}, year = {2025}, month = oct, volume = {992}, number = {2}, eid = {L25}, pages = {L25}, doi = {10.3847/2041-8213/ae0b4f}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992L..25L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, kinematics, local counterpart, non-agn, non-jwst}, altmetric = {182950411}, month_numeric = {10} }

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Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

P. Rinaldi, N. Bonaventura, G. H. Rieke, and 31 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS arXiv

We analyze 99 photometrically selected Little Red Dots (LRDs) at z \ensuremath≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes \ensuremath≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest- frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M\ens uremath⋆/M\ensuremath⊙)=9.07‑0.08+0.11 for pure stellar models with AV\ensuremath≈1.16‑0.21+0.11 mag, and log10(M\ensuremath⋆/M\ensuremath⊙)=9.67‑0.27 +0.17 for models including active galactic nuclei (AGNs) with AV\ensuremath≈2.74‑0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad H\ensuremathα is detected in 40% (FWHM = 1200–2900 km s^‑1), and one source shows broad H\ensuremathβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

@article{2025ApJ...992...71R, author = {{Rinaldi}, P. and {Bonaventura}, N. and {Rieke}, G. H. and {Alberts}, S. and {Caputi}, K. I. and {Baker}, W. M. and {Baum}, S. and {Bhatawdekar}, R. and {Bunker}, A. J. and {Carniani}, S. and {Curtis-Lake}, E. and {D'Eugenio}, F. and {Egami}, E. and {Ji}, Z. and {Johnson}, B. D. and {Hainline}, K. and {Helton}, J. M. and {Lin}, X. and {Lyu}, J. and {Ma}, Z. and {Maiolino}, R. and {P{\'e}rez-Gonz{\'a}lez}, P. G. and {Rieke}, M. and {Robertson}, B. E. and {Shivaei}, I. and {Stone}, M. and {Sun}, Y. and {Tacchella}, S. and {{\"U}bler}, H. and {Williams}, C. C. and {Willmer}, C. N. A. and {Willott}, C. and {Zhang}, J. and {Zhu}, Y.}, title = {{Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots}}, journal = {\apj}, keywords = {James Webb Space Telescope, Active galactic nuclei, Near infrared astronomy, Galaxy evolution, Galaxy formation, 2291, 16, 1093, 594, 595}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {71}, pages = {71}, doi = {10.3847/1538-4357/adfa10}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992...71R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, morphology, photometry, sed}, eprint = {2411.14383}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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Ultra-Strongly Self-Interacting Dark Matter: From Phenomenology to Astrophysical Observables

M. Grant Roberts, Wolfgang Altmannshofer, Pierce Giffin, and 1 more author

arXiv e-prints, Oct 2025

Abs ADS arXiv

We develop a minimal, testable framework for two-component self- interacting dark matter (SIDM) in which a dominant, moderately self-interacting species coexists with an ultra-strongly self- interacting subcomponent (uSIDM). A light vector mediator induces velocity-dependent self-scattering, while early-universe dynamics - standard 2 \to 2 annihilation supplemented by interconversion χ_1χ_1 \to χ_2χ_2 - determine the relic abundance analytically. From observations of dwarf and low surface brightness galaxy rotation curves, as well as strong cluster lensing, we place constraints on the microphysics parameters. From these constrained regions, we map the microphysics to effective \textbackslashtexttt{ETHOS} parameters and evolve the linear power spectrum in \textbackslashtexttt{CLASS}. We then confront the model with direct-detection constraints and place an upper bound on our parameter space. We identify a region where: (1) the SIDM dominant component attains σ_\rmeff/m = 20 - 40~\textcm^2\textg^-1 at dwarf velocities while satisfying cluster upper bounds σ_\rmeff/m < 0.13~\rmcm^2\rmg^-1; (2) a subpercent uSIDM fraction drives accelerated gravothermal collapse in early halos, providing seeds relevant to high-redshift quasar formation and “little red dots”; and (3) the small-scale cutoff in the matter power spectrum remains consistent with Lyman-α and satellite counts, but exhibits non-standard features, potentially discernible with future observations. The allowed space can be organized by the mediator-to-DM mass ratio and the late-time uSIDM fraction, with a narrow window singled out by the combined cosmological and astrophysical requirements.

@article{2025arXiv251018142R, author = {{Roberts}, M. Grant and {Altmannshofer}, Wolfgang and {Giffin}, Pierce and {Profumo}, Stefano}, title = {{Ultra-Strongly Self-Interacting Dark Matter: From Phenomenology to Astrophysical Observables}}, journal = {arXiv e-prints}, keywords = {High Energy Physics - Phenomenology, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = oct, eid = {arXiv:2510.18142}, pages = {arXiv:2510.18142}, archiveprefix = {arXiv}, eprint = {2510.18142}, primaryclass = {hep-ph}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251018142R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, multi-wavelength, simulation, theory, x-ray}, month_numeric = {10} }

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Faint active galactic nuclei supplied 31-75% of hydrogen-ionizing photons at z>5

Mainak Singha, Sangeeta Malhotra, and James Ely Rhoads

arXiv e-prints, Oct 2025

Abs ADS arXiv

The origin of the ionizing photons that completed hydrogen reionization remains debated. Using recent JWST and ground-based surveys at 4.5 <= z <= 6.5, we construct a unified rest-UV AGN luminosity function that separates unobscured Type I and obscured Type II populations, and show that “little red dots” and X-ray selected sources are magnitude-filtered subsets of Type I with a mixture fraction eta = 0.10 +/- 0.02. We anchor the Lyman- continuum (LyC) escape fraction to outflow incidence and geometric clearing rather than assuming quasar-like values for all classes, and propagate uncertainties through a joint fit. Integrating over -27 < M_UV < -17, AGN inject Ndot_ion,AGN = (3.77 +1.08/-0.95) x 10\^51 s\^-1 Mpc\^-3, nearly twice earlier estimates and comparable to the Ly-alpha inferred requirement at z \raisebox-0.5ex~6. When combined with the JWST galaxy UV luminosity function and a harder stellar ionizing efficiency of log10(xi_ion) = 25.7, AGN contribute 31-75% of the total ionizing photons for representative galaxy escape fractions f_esc,gal = 0.03-0.20. The resulting hydrogen photoionization rate, Gamma_HI \raisebox-0.5ex~(0.5-2) x 10\^-12 s\^-1 at z \raisebox-0.5ex~5-6, lies squarely within the Ly-alpha forest constraints once mean free paths and IGM clumpiness are accounted for, remaining consistent for combined AGN-galaxy models up to f_esc,gal <= 5%. These results suggest that AGN and galaxies jointly sustained the ionizing background during the final stages of reionization, with AGN remaining a major but not exclusive contributor.

@article{2025arXiv251026990S, author = {{Singha}, Mainak and {Malhotra}, Sangeeta and {Ely Rhoads}, James}, title = {{Faint active galactic nuclei supplied 31-75\% of hydrogen-ionizing photons at z>5}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.26990}, pages = {arXiv:2510.26990}, archiveprefix = {arXiv}, eprint = {2510.26990}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251026990S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, multi-wavelength, photometry}, month_numeric = {10} }

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JWST/NIRSpec Observations of High-ionization Emission Lines in Galaxies at High Redshift

Mengtao Tang, Daniel P. Stark, Adèle Plat, and 7 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS arXiv

JWST spectroscopy has built large emission line samples at z \ensuremath≳ 4, but it has yet to confidently reveal many galaxies with the hard radiation fields commonly associated with active galactic nucleus photoionization. While this may indicate a weaker UV ionizing spectrum in many z > 4 active galactic nuclei or obscuration from dense neutral gas and dust, the complete picture remains unclear owing to the small number of deep rest-UV spectra. Here, we characterize the strength of high-ionization lines in 53 new galaxies observed with NIRSpec R = 2700 grating spectroscopy. We present new detections of narrow N V \ensuremathλ1240 in two galaxies. One is a previously confirmed z = 6.98 little red dot (LRD) with broad H\ensuremathβ, and the other is a z = 8.72 galaxy with a narrow-line spectrum. Neither source exhibits C IV or He II emission, indicating large N V/C IV and N V/He II ratios that may reflect a combination of nitrogen-enhancement and resonant scattering effects. We investigate the incidence of narrow high- ionization lines in a large database of 851 NIRSpec grating spectra, and we separately quantify the fraction of LRDs with narrow high-ionization UV emission lines. Our results likely suggest that hard radiation fields are indeed present in a small subset of LRDs (12.5‑10.4+23.7%) and UV-selected galaxies (2.2‑1.0+1.7%) at z > 4. The identification of narrow high- ionization lines in the population of LRDs with strong Balmer absorption suggests that the dense neutral hydrogen gas may not uniformly cover the nucleus. The strong N V (coupled with weak C IV and He II) suggests that efforts to identify high-ionization lines should extend down in wavelength to the N V doublet.

@article{2025ApJ...991..217T, author = {{Tang}, Mengtao and {Stark}, Daniel P. and {Plat}, Ad{\`e}le and {Feltre}, Anna and {Katz}, Harley and {Senchyna}, Peter and {Mason}, Charlotte A. and {Whitler}, Lily and {Chen}, Zuyi and {Topping}, Michael W.}, title = {{JWST/NIRSpec Observations of High-ionization Emission Lines in Galaxies at High Redshift}}, journal = {\apj}, keywords = {High-redshift galaxies, Active galactic nuclei, 734, 16}, year = {2025}, month = oct, volume = {991}, number = {2}, eid = {217}, pages = {217}, doi = {10.3847/1538-4357/adfd57}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...991..217T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, non-agn, spectroscopy}, eprint = {2505.06359}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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A Novel Formation Channel for Supermassive Black Hole Binaries in the Early Universe via Primordial Black Holes

Saiyang Zhang, Boyuan Liu, and Volker Bromm

The Astrophysical Journal, Oct 2025

Abs DOI ADS arXiv

We present a novel formation channel for supermassive black hole (SMBH) binaries in the early Universe, driven by primordial black holes (PBHs). Using high-resolution hydrodynamical simulations, we explore the role of massive PBHs (m_BH \ensuremath∼ 10^6 M_\ensuremath⊙) in catalyzing the formation of direct-collapse black holes (DCBHs), providing a natural in situ pathway for binary SMBH formation. PBHs enhance local overdensities, accelerate structure formation, and exert thermal feedback on the surrounding medium via accretion. Lyman–Werner radiation from accreting PBHs suppresses H_2 cooling, shifting the dominant gas coolant to atomic hydrogen. When combined with significant baryon–dark matter streaming velocities (v_b\ensuremathχ \ensuremath≳ 0.8\ensuremathσ_b\ensuremathχ, where \ensuremathσ_b\ensuremathχ is the rms streaming velocity), these effects facilitate the formation of dense, gravitationally unstable atomically cooling gas clouds in the PBH’s wake. These clouds exhibit sustained high inflow rates (Ṁinfall\ensuremath≳0.1‑0.01M\ensuremath⊙ yr^‑1), providing ideal conditions for DCBH formation from rapidly growing supermassive stars of \ensuremath∼10^5 M_\ensuremath⊙ at redshift z \ensuremath∼ 20–10. The resulting systems form SMBH binaries with initial mass ratios q\ensuremath∼O(0.1) and separations of \ensuremath∼10 pc. Such PBH-DCBH binaries provide testable predictions for JWST and Atacama Large Millimeter/submillimeter Array, potentially explaining select high-z sources like little red dots, and represent gravitational-wave sources for future missions like LISA and TianQin—bridging early-Universe black hole physics, multimessenger astronomy, and dark matter theory.

@article{2025ApJ...992..136Z, author = {{Zhang}, Saiyang and {Liu}, Boyuan and {Bromm}, Volker}, title = {{A Novel Formation Channel for Supermassive Black Hole Binaries in the Early Universe via Primordial Black Holes}}, journal = {\apj}, keywords = {Dark matter, Early universe, Galaxy formation, Population III stars, Supermassive black holes, 353, 435, 595, 1285, 1663}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {136}, pages = {136}, doi = {10.3847/1538-4357/ae061c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992..136Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, eprint = {2508.00774}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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Unveiling Extended Components of ’Little Red Dots’ in Rest-Frame Optical

Yiyang Zhang, Xuheng Ding, Lilan Yang, and 26 more authors

arXiv e-prints, Oct 2025

Abs ADS arXiv

Recent JWST observations have revealed a population of red, compact, high-redshift objects called ’Little Red Dots’(LRD), whose host components have remained largely unconstrained, possibly due to their extreme compactness. Current morphological studies have been limited by small samples, as well as by insufficient imaging depth, which may not allow reliable separation between point-like and extended components, leaving the existence and properties of extended components in LRD largely unconstrained. Here, we perform the image stacking analysis of 217 LRDs in four NIRCam bands, representing the largest and homogeneous sample observed from COSMOS-Web survey to date. Our results reveal an unambiguous detection of faint extended emission in the F444W band, with a typical size of \raisebox-0.5ex\textasciitilde200 parsecs and magnitude of \raisebox-0.5ex\textasciitilde27.7 AB at z\raisebox-0.5ex\textasciitilde6.5. We perform four-band photometric SED fitting based on galaxy templates and derive a stellar mass of 8.91+-\raisebox-0.5ex\textasciitilde0.1 logM_sun. Given this stellar mass, the host galaxy is compact, i.e., \raisebox-0.5ex\textasciitilde2.5 times smaller than star-forming populations at similar mass, and the typical black hole mass of LRDs is elevated by \raisebox-0.5ex\textasciitilde1.5 dex above the local MBH-M* relation. This work provides direct observational evidence for the existence of LRD host galaxies and offers crucial insights into the growth of the host galaxy and the co-evolution of galaxies and their black holes within the first billion years after the Big Bang.

@article{2025arXiv251025830Z, author = {{Zhang}, Yiyang and {Ding}, Xuheng and {Yang}, Lilan and {Lambrides}, Erini and {Akins}, Hollis and {Battisti}, Andrew J. and {Casey}, Caitlin M. and {Chen}, Chang-hao and {Cox}, Isa and {Faisst}, Andreas and {Franco}, Maximilien and {Haghjoo}, Aryana and {Ho}, Luis C. and {Inayoshi}, Kohei and {Jin}, Shuowen and {Karmen}, Mitchell and {Koekemoer}, Anton M. and {Kartaltepe}, Jeyhan S. and {Liao}, Kai and {Gozaliasl}, Ghassem and {Onoue}, Masafusa and {Kokorev}, Vasily and {Roy}, Namrata and {Rich}, R. Michael and {Silverman}, John D. and {Tanaka}, Takumi S. and {You}, Bei and {Yesuf}, Hassen M. and {Zavala}, Jorge A.}, title = {{Unveiling Extended Components of 'Little Red Dots' in Rest-Frame Optical}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.25830}, pages = {arXiv:2510.25830}, archiveprefix = {arXiv}, eprint = {2510.25830}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251025830Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, photometry, sed}, month_numeric = {10} }

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On the Variability Features of Active Galactic Nuclei in Little Red Dots

Shuying Zhou, Mouyuan Sun, Zijian Zhang, and 2 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS arXiv

The high-redshift (z > 4) compact sources with “V-shaped” spectral energy distributions, known as Little Red Dots (LRDs), were discovered by the James Webb Space Telescope and provide valuable clues to the physics of active galactic nuclei (AGNs) in the early Universe. The nature of LRDs is controversial. Recently, several studies have investigated LRDs through variability, a characteristic feature of AGNs. These studies explore LRD variability by extrapolating empirical relationships from local quasars. Here, we adopt the Corona-heated Accretion- disk Reprocessing (CHAR) model, which is motivated by accretion physics and is applicable to reproducing AGN conventional variability, to study the variability of 22 LRDs in W. L. Tee et al. Our results indicate that the observed variability in LRDs is dominated by measurement uncertainties. Within the CHAR model, the lack of variability in LRDs can be explained by two scenarios: either AGNs contribute \ensuremath≲30% of the observed luminosities, or they are intrinsically luminous AGNs. We use simulations to demonstrate the observational requirements to effectively investigate LRDs via variability with the following criteria: first, the sample has about 200 LRDs; second, each LRD has two observations separated by at least 2 yr in the observed frame; third, the photometric uncertainty is \ensuremath≤0.07 mag. If the LRDs still lack variability under these conditions, the time–domain study would provide independent evidence that the accretion mode of LRDs differs significantly from low- redshift quasars.

@article{2025ApJ...991..137Z, author = {{Zhou}, Shuying and {Sun}, Mouyuan and {Zhang}, Zijian and {Chen}, Jie and {Ho}, Luis C.}, title = {{On the Variability Features of Active Galactic Nuclei in Little Red Dots}}, journal = {\apj}, keywords = {Accretion, Active galactic nuclei, High-redshift galaxies, Supermassive black holes, 14, 16, 734, 1663}, year = {2025}, month = oct, volume = {991}, number = {2}, eid = {137}, pages = {137}, doi = {10.3847/1538-4357/adfd5f}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...991..137Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, sed, theory, variability}, eprint = {2508.16795}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {10} }

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The mechanism for creating“dynamical gravastar” black hole mimickers can also explain formation of “little red dots”

Stephen L. Adler

arXiv e-prints, Sep 2025

Abs ADS arXiv

We argue that a high pressure phase transition of relativistic matter to a state with negative energy density, which leads to the formation of horizonless black hole mimickers, can also give rise to the appearance of “little red dots”. The energy source for the dots is the release of latent energy from the phase transition, and their redness is a result of this release taking place in a central region of exponentially small positive g_00, and hence very high gravitational redshift.

@article{2025arXiv250923490A, author = {{Adler}, Stephen L.}, title = {{The mechanism for creating``dynamical gravastar'' black hole mimickers can also explain formation of ``little red dots''}}, journal = {arXiv e-prints}, keywords = {General Relativity and Quantum Cosmology}, year = {2025}, month = sep, eid = {arXiv:2509.23490}, pages = {arXiv:2509.23490}, archiveprefix = {arXiv}, eprint = {2509.23490}, primaryclass = {gr-qc}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250923490A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, non-agn, spectroscopy, theory}, month_numeric = {9} }

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COSMOS-web: The Overabundance and Physical Nature of “Little Red Dots”—Implications for Early Galaxy and SMBH Assembly

Hollis B. Akins, Caitlin M. Casey, Erini Lambrides, and 38 more authors

The Astrophysical Journal, Sep 2025

Abs DOI ADS arXiv

JWST has revealed a population of compact and extremely red galaxies at z \ensuremath≳ 4, which likely host active galactic nuclei (AGNs). We present a sample of 434 “little red dots” (LRDs), selected from the 0.54 deg^2 COSMOS-Web survey. We fit galaxy and AGN spectral energy distribution models to derive redshifts and physical properties; the sample spans z \ensuremath∼ 5–9 after removing brown dwarf contaminants. As a thought experiment, we consider two extreme physical scenarios: either LRDs are all AGNs, and their continuum emission is dominated by the accretion disk, or they are all compact star-forming galaxies, and their continuum is dominated by stars. If LRDs are AGN-dominated, our sample exhibits bolometric luminosities \ensuremath∼10^45‑47 erg s^‑1, spanning the gap between JWST AGNs in the literature and bright, rare quasars. We derive a bolometric luminosity function (LF) \ensuremath∼ 100 times the (UV- selected) quasar LF, implying a nonevolving black hole accretion density of \ensuremath∼10^‑4M_\ensuremath⊙ yr^‑1 Mpc^‑3 from z \ensuremath∼ 2–9. By contrast, if LRDs are dominated by star formation, we derive stellar masses \ensuremath∼10^8.5‑10 M_\ensuremath⊙. MIRI/F770W is key to deriving accurate stellar masses; without it, we derive a mass function inconsistent with \ensuremathΛ cold dark matter. The median stellar mass profile is broadly consistent with the maximal surface densities seen in the nearby Universe, though the most massive objects exceed this limit, requiring substantial AGN contribution to the continuum. Nevertheless, stacking all available X-ray, mid-IR, far-IR/submillimeter, and radio data yields nondetections. Whether dominated by dusty AGNs or compact star-formation, the high masses/luminosities and remarkable abundance of LRDs implies a dominant mode of early galaxy/SMBH growth.

@article{2025ApJ...991...37A, author = {{Akins}, Hollis B. and {Casey}, Caitlin M. and {Lambrides}, Erini and {Allen}, Natalie and {Andika}, Irham T. and {Brinch}, Malte and {Champagne}, Jaclyn B. and {Cooper}, Olivia and {Ding}, Xuheng and {Drakos}, Nicole E. and {Faisst}, Andreas and {Finkelstein}, Steven L. and {Franco}, Maximilien and {Fujimoto}, Seiji and {Gentile}, Fabrizio and {Gillman}, Steven and {Gozaliasl}, Ghassem and {Harish}, Santosh and {Hayward}, Christopher C. and {Hirschmann}, Michaela and {Ilbert}, Olivier and {Kartaltepe}, Jeyhan S. and {Kocevski}, Dale D. and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Liu}, Daizhong and {Long}, Arianna S. and {McCracken}, Henry Joy and {McKinney}, Jed and {Onoue}, Masafusa and {Paquereau}, Louise and {Renzini}, Alvio and {Rhodes}, Jason and {Robertson}, Brant E. and {Shuntov}, Marko and {Silverman}, John D. and {Tanaka}, Takumi S. and {Toft}, Sune and {Trakhtenbrot}, Benny and {Valentino}, Francesco and {Zavala}, Jorge}, title = {{COSMOS-web: The Overabundance and Physical Nature of ``Little Red Dots''{\textemdash}Implications for Early Galaxy and SMBH Assembly}}, journal = {\apj}, keywords = {Active galactic nuclei, Quasars, High-redshift galaxies, Galaxies, 16, 1319, 734, 573}, year = {2025}, month = sep, volume = {991}, number = {1}, eid = {37}, pages = {37}, doi = {10.3847/1538-4357/ade984}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...991...37A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {181507350}, lrdkeys = {black hole mass, early universe, jwst, photometry, sed}, eprint = {2406.10341}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {9} }

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How similar are narrow-line Seyfert 1 galaxies and high-z type 1 AGN?

M. Berton, E. Järvelä, A. Tortosa, and 1 more author

arXiv e-prints, Sep 2025

Abs DOI ADS arXiv

The recent observations of highly accreting supermassive black holes (SMBH) at very high redshift (>4) with the James Webb Space Telescope (JWST) allowed us to shed light for the very first time on the early evolutionary phases of active galactic nuclei (AGN). Perhaps unsurprisingly, several of the physical properties observed in these new objects, including those known as little red dots (LRDs), are closely reminiscent of the low- mass and high-Eddington AGN in the local Universe, and in particular of the class of narrow-line Seyfert 1 (NLS1) galaxies. However, some differences also emerged, likely due to the radically different evolutionary path and the environment where LRDs and NLS1s live. In this work, we review the multiwavelength properties of local NLS1s and compare them with type 1 AGN found at high-z, showing that despite some differences, the study of NLS1s can be extremely useful to better understand the extreme accretion physics of high-z quasars and the early stages of AGN evolution.

@article{2025arXiv250903576B, author = {{Berton}, M. and {J{\"a}rvel{\"a}}, E. and {Tortosa}, A. and {Mazzucchelli}, C.}, title = {{How similar are narrow-line Seyfert 1 galaxies and high-z type 1 AGN?}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = sep, eid = {arXiv:2509.03576}, pages = {arXiv:2509.03576}, doi = {10.48550/arXiv.2509.03576}, archiveprefix = {arXiv}, eprint = {2509.03576}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250903576B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, local counterpart, multi-wavelength}, month_numeric = {9} }

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An Upper Limit of 10^6 M_\ensuremath⊙ in Dust from ALMA Observations in 60 Little Red Dots

Caitlin M. Casey, Hollis B. Akins, Steven L. Finkelstein, and 9 more authors

The Astrophysical Journal Letters, Sep 2025

Abs DOI ADS arXiv

By virtue of their red color, the dust in little red dots (LRDs) has been thought to be of appreciable influence, whether that dust is distributed in a torus around a compact active galactic nucleus or diffuse in the interstellar medium of nascent galaxies. In C. M. Casey et al. we predicted that, based on the compact sizes of LRDs (unresolved in JWST NIRCam imaging), detection of an appreciable dust mass would be unlikely. Here we present follow-up Atacama Large Millimeter/submillimeter Array 1.3 mm continuum observations of a sample of 60 LRDs drawn from H. B. Akins et al. None of the 60 LRDs are detected in imaging that reaches an average depth of \ensuremathσ_rms = 22 \ensuremathμJy. A stack of the 60 LRDs also results in a nondetection, with an inverse-variance weighted flux density measurement of S_1._3 mm = 2.1 \ensuremath\pm 2.9 \ensuremathμJy. This observed limit translates to a 3\ensuremathσ upper limit of 10^6 M_\ensuremath⊙ in LRDs’ dust mass, and \ensuremath≲10^11 L_\ensuremath⊙ in total dust luminosity; both are a factor of 10\texttimes deeper than previous submillimeter stack limits for LRDs. These results are consistent with either the interpretation that LRDs are reddened due to compact but modest dust reservoirs (with A_V \ensuremath∼ 2–4) or, alternatively, that instead of being reddened by dust, they have extreme Balmer breaks generated by dense gas (>10^9 cm^‑3) enshrouding a central black hole.

@article{2025ApJ...990L..61C, author = {{Casey}, Caitlin M. and {Akins}, Hollis B. and {Finkelstein}, Steven L. and {Franco}, Maximilien and {Fujimoto}, Seiji and {Liu}, Daizhong and {Long}, Arianna S. and {Magdis}, Georgios and {Manning}, Sinclaire M. and {McKinney}, Jed and {Shuntov}, Marko and {Tanaka}, Takumi S.}, title = {{An Upper Limit of {}10$^{6}$ M$\_{{\ensuremath{\odot}}}$ in Dust from ALMA Observations in 60 Little Red Dots}}, journal = {\apjl}, keywords = {Interstellar dust, Interstellar reddening, High-redshift galaxies, Astrophysical black holes, 836, 853, 734, 98}, year = {2025}, month = sep, volume = {990}, number = {2}, eid = {L61}, pages = {L61}, doi = {10.3847/2041-8213/adfa91}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...990L..61C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, non-agn, non-jwst, photometry, sed}, altmetric = {181645757}, eprint = {2505.18873}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {9} }

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Little Red Dots as direct-collapse black hole nurseries

Elia Cenci and Melanie Habouzit

Monthly Notices of the Royal Astronomical Society, Sep 2025

Abs DOI ADS arXiv

The James Webb Space Telescope recently uncovered a population of massive black holes (BHs) in the first billion years after the big bang. Among these high-redshift BH candidates, observations have identified a class of active galactic nuclei candidates, dubbed Little Red Dots (LRDs), with extraordinarily compact gas reservoirs and peculiar spectral features. LRDs clearly emerge at redshift and their abundance declines by . Recent theoretical studies have explored the link between LRDs and the formation of heavy BH seeds in the early Universe, such as direct-collapse BHs (DCBHs). Here, we present results from preliminary runs for the melira cosmological hydrodynamical simulations, where we implement an accurate model for DCBH formation, accounting for the Lyman–Werner radiation field and mass-inflow rates in the target host haloes. We aim to test whether or not DCBH formation could lead to systems resembling those hypothesized for LRDs. We find that the population of newly formed DCBHs in the simulations exhibits a steep decline at , akin to the emergence of LRDs, primarily driven by reduced inflows. The birth of DCBHs is associated with a significant gas compaction event, followed by a phase of intense luminosity in the after their birth, and subsequently by the formation of the first Population III stars in these very haloes. If these DCBHs nurseries are associated with LRDs, then it could explain their weak emission from X-rays and hot dust.

@article{2025MNRAS.542.2597C, author = {{Cenci}, Elia and {Habouzit}, Melanie}, title = {{Little Red Dots as direct-collapse black hole nurseries}}, journal = {\mnras}, keywords = {methods: numerical, galaxies: active, galaxies: formation, quasars: supermassive black holes}, year = {2025}, month = sep, volume = {542}, number = {3}, pages = {2597-2609}, doi = {10.1093/mnras/staf1362}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.542.2597C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {180482705}, lrdkeys = {black hole mass, early universe, jwst, simulation, x-ray}, eprint = {2508.14897}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {9} }

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A two-phase model of galaxy formation: IV. Seeding and growing supermassive black holes in dark matter halos

Yangyao Chen, Houjun Mo, and Huiyuan Wang

arXiv e-prints, Sep 2025

Abs ADS arXiv

We present a theoretical framework for seeding and growing supermassive black holes (SMBHs) in dark-matter halos along their assembly histories. Seeds are bred out of Pop-III stars formed during the first collapse of pristine gas in mini-halos that have reached the \rm H_2-cooling limit, modulated by UV radiation from star formation and dynamical heating from fast halo assembly. Such breeding persists until the enrichment of the intergalactic medium (IGM) enables Pop-II stars to form. Post-seeding growth of black holes (BHs) is driven by distinct channels, starting with episodic super-Eddington accretion associated with nuclear bursts induced by global disturbances of galaxies, followed by sustained sub-Eddington accretion via capturing sub-clouds formed in self-gravitating gas clouds (SGCs) in halos of fast assembly, and ending with merger-dominated, quiescent growth. We implement the model in subhalo merger trees to build a coherent framework to follow the SMBH-galaxy-halo co-evolution over their full lives in the full structure hierarchy. BH seeds are bred with a broad mass spectrum of M_\rm BH = 10–10^5\,\rm M_⊙at z ≈20–30 in mini-halos with masses of 10^5–10^8\,\rm M_⊙. Nuclear bursts provide the key condition for seeds to grow into SMBHs. The M_\rm BH-M_* relation is a multi-piece, redshift-dependent function shaped by the interplay among different growth channels. Our model predictions are broadly consistent with existing observations; especially, a population of BHs reminiscent of ‘little red dots’ (LRDs) discovered by JWST naturally results from the seeding and growing processes. Potential future tests of the model are discussed.

@article{2025arXiv250903283C, author = {{Chen}, Yangyao and {Mo}, Houjun and {Wang}, Huiyuan}, title = {{A two-phase model of galaxy formation: IV. Seeding and growing supermassive black holes in dark matter halos}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, Solar and Stellar Astrophysics}, year = {2025}, month = sep, eid = {arXiv:2509.03283}, pages = {arXiv:2509.03283}, archiveprefix = {arXiv}, eprint = {2509.03283}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250903283C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, month_numeric = {9} }

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Irony at z=6.68: a bright AGN with forbidden Fe emission and multi-component Balmer absorption

Francesco D’Eugenio, Erica Nelson, Xihan Ji, and 11 more authors

arXiv e-prints, Sep 2025

Abs ADS arXiv

We present the deepest medium-resolution JWST/NIRSpec spectroscopy to date of a bright Little Red Dot (LRD) AGN, Irony at z=6.68. The data reveal broad Balmer emission from Hα-Hδ and Balmer absorption in Hα-Hε. The absorption lines are kinematically split: Hα is blueshifted while higher-order lines are redshifted suggesting complex gas kinematics; their relative ratios are inconsistent with a single, passive absorbing screen. The line depths require absorption of both the BLR and the continuum, ruling out a stellar origin, consistent with the smooth Balmer break. We fit the broad Hγ-Hα lines and find the data favor a double-Gaussian effective profile, although exponential wings are evident. Depending on the adopted profile, single-epoch virial estimates give log(M_∙/M_⊙)=7.86-8.39 and λ_\rm Edd=1.7-0.4. The dynamical mass implied by the narrow lines is low log(Mdyn/M_⊙)=9.1, suggesting an overmassive black hole. The narrow lines display little attenuation, A_V<0.5 mag; while broad Hα/Hβ\sim9 and the broad Balmer decrements are inconsistent with standard dust attenuation curves, suggesting collisional processes. The forbidden-line spectrum includes auroral [S II] and [N II], and a forest of [Fe II] lines. Line ratios and kinematics indicate a stratified narrow-line region with both low (n_\rm e=420 cm^-3) and high densities (n_\rm ersim 6.3\times10^5 cm^-3). We detect metal absorption lines in both the optical (Ca II and Na I) and UV range (Fe II UV1-UV3). Our results support a picture of a compact AGN embedded in a dense, high covering-factor and stratified cocoon, with complex neutral-gas kinematics. While the choice of broad-line profile affects the virial estimates of M_∙, we find the effect to be of order 0.6 dex between the different approaches.

@article{2025arXiv251000101D, author = {{D'Eugenio}, Francesco and {Nelson}, Erica and {Ji}, Xihan and {Baggen}, Josephine and {Greene}, Jenny and {Labb{\'e}}, Ivo and {Pezzulli}, Gabriele and {Brown}, Vanessa and {Maiolino}, Roberto and {Matthee}, Jorryt and {Terlevich}, Elena and {Terlevich}, Roberto and {Torralba}, Alberto and {Carniani}, Stefano}, title = {{Irony at z=6.68: a bright AGN with forbidden Fe emission and multi-component Balmer absorption}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2510.00101}, pages = {arXiv:2510.00101}, archiveprefix = {arXiv}, eprint = {2510.00101}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251000101D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, kinematics, spectroscopy}, month_numeric = {9} }

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Discovery of Multiply Ionized Iron Emission Powered by an Active Galactic Nucleus in a z\raisebox-0.5ex\textasciitilde7 Little Red Dot

Erini Lambrides, Rebecca Larson, Taylor Hutchison, and 50 more authors

arXiv e-prints, Sep 2025

Abs ADS arXiv

Some of the most puzzling discoveries of NASA’s JWST in the early Universe surround the surprising abundance of compact red sources, which show peculiar continuum shapes and broad hydrogen spectral lines. These sources, dubbed “Little Red Dots” or LRDs, have been the subject of intense inquiry in the literature. Any of the proposed explanations, from accreting super-massive black holes ensconced in ultra-dense gas to extremely compact star-systems, has significant implications for the earliest phases of galaxy evolution. Part of the difficulty in concretely identifying the physical mechanisms that drive their rest ultra-violet/optical spectral properties is the lack of bona fide signatures – either star-formation or accreting super-massive black hole, that uniquely discriminate between competing interpretations. In this work, we report the discovery of several spectral features that strongly favor the existence of an accreting super-massive black hole in an LRD witnessed in the first 800 Myr of cosmic time, including several rare iron transitions and a possible [FeVII]. Additionally, we report on the properties of significant Balmer absorption and find that the small widths and relative depths of the absorption feature suggest the source of the absorber is at or beyond the outer edge of the broad-line region and does it fully cover the accreting SMBH in the center of the system. The detection of these iron features, coupled with the properties of the Balmer absorption, unveils an alternative scenario for LRDs – one where there are direct sight-lines from the accretion disk to gas on scales at (or beyond) the broad-line gas region.

@article{2025arXiv250909607L, author = {{Lambrides}, Erini and {Larson}, Rebecca and {Hutchison}, Taylor and {Arrabal Haro}, Pablo and {Wang}, Bingjie and {Welch}, Brian and {Kocevski}, Dale D. and {Richardson}, Chris T. and {Papovich}, Casey and {Trump}, Jonathan R. and {Bosman}, Sarah E. I. and {Rigby}, Jane R. and {Finkelstein}, Steven L. and {Barro}, Guillermo and {Antwi-Danso}, Jacqueline and {Long}, Arianna and {Taylor}, Anthony J. and {Cann}, Jenna and {McKaig}, Jeffrey and {Koekemoer}, Anton M. and {Cleri}, Nikko J. and {Akins}, Hollis B. and {Bagley}, Mic B. and {Berg}, Danielle A. and {Bromm}, Volker and {Chisholm}, John and {Chworowsky}, Katherine and {Coffin}, Sadie and {Cooper}, M. C. and {Cooper}, Olivia and {Cox}, Isa and {Dickinson}, Mark and {Ferguson}, Henry C. and {Franco}, Maximilien and {Gardner}, Jonathan P. and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Huertas-Company}, Marc and {Jung}, Intae and {Kartaltepe}, Jeyhan S. and {Khullar}, Gourav P. and {Lucas}, Ray A. and {McGrath}, Elizabeth J. and {Morales}, Alexa M. and {Olivier}, Grace M. and {Ch{\'a}vez Ortiz}, {\'O}scar A. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Pirzkal}, Norbert and {Somerville}, Rachel S. and {Vanderhoof}, Brittany and {Weiner}, Benjamin J. and {Yung}, L. Y. Aaron and {Zavala}, Jorge A.}, title = {{Discovery of Multiply Ionized Iron Emission Powered by an Active Galactic Nucleus in a z\raisebox{-0.5ex}\textasciitilde7 Little Red Dot}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.09607}, pages = {arXiv:2509.09607}, archiveprefix = {arXiv}, eprint = {2509.09607}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250909607L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, month_numeric = {9} }

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No Luminous Little Red Dots: A Sharp Cutoff in Their Luminosity Function

Yilun Ma, Jenny E. Greene, Marta Volonteri, and 14 more authors

arXiv e-prints, Sep 2025

Abs ADS arXiv

One of the most surprising results of early James Webb Space Telescope (JWST) observations is the discovery of an abundance of red, compact, broad-line objects dubbed “little red dots” (LRDs) at z>4. Their spatial density (\sim10^-4-10^-5\,\mathrmcMpc^-3) is 100 times more abundant than UV-selected quasars at those redshift if one extrapolates the quasar luminosity function (QLF) down to the LRD regime. However, whether LRDs dominate black hole accretion at quasar-like luminosities (L_\mathrmbolrsim 10^45-46\,\mathrmerg s^-1) remains unanswered, as probing the bright end of the LRD luminosity function requires a much larger area than those able to be surveyed by JWST. In this work, we present our search for the brightest LRDs (K<23.7) at 4.5<z<4.9 using wide-area multiwavelength imaging surveys from the near-UV to the infrared bands. With over 15 square degrees of sky coverage, we only identify one single LRD candidate at z_\mathrmphot\approx4.6, which translates into a spatial density of n(M_5100<-23.5)\approx10^-8\,\mathrmcMpc^-3 – this is nearly 10 times less abundant than the UV-selected quasars at similar optical luminosity. When combined with the LRD sample identified by JWST at the same redshift range, we find a sharp cutoff in the optical luminosity function at λL_5100\approx2.5\times10^44\,\mathrmerg s^-1, while the QLF turnover occurs at rsim20 times higher luminosity. We therefore confirm the exclusively low-luminosity nature of LRDs, ruling out that LRDs are the counter parts of quasars. Furthermore, we speculate that, if the shape of the luminosity function holds up, it points to LRDs being powered by low-mass black holes with a narrow range of Eddington-level accretion rates.

@article{2025arXiv250902662M, author = {{Ma}, Yilun and {Greene}, Jenny E. and {Volonteri}, Marta and {Goulding}, Andy D. and {Setton}, David J. and {Annunziatella}, Marianna and {Egami}, Eiichi and {Fan}, Xiaohui and {Kokorev}, Vasily and {Labbe}, Ivo and {Lin}, Xiaojing and {Marchesini}, Danilo and {Matthee}, Jorryt and {Nanayakkara}, Themiya and {Robbins}, Luke and {Sajina}, Anna and {Sawicki}, Marcin}, title = {{No Luminous Little Red Dots: A Sharp Cutoff in Their Luminosity Function}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = sep, eid = {arXiv:2509.02662}, pages = {arXiv:2509.02662}, archiveprefix = {arXiv}, eprint = {2509.02662}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250902662M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, multi-wavelength, photometry}, month_numeric = {9} }

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What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?

Krisztina Perger, Judit Fogasy, and Sándor Frey

Universe, Sep 2025

Abs DOI ADS arXiv

The real nature of little red dots (LRDs), a class of very compact galaxies in the early Universe recently discovered by the James Webb Space Telescope, is still poorly understood. The most popular theories competing to interpret the phenomena include active galactic nuclei and enhanced star formation in dusty galaxies. To date, however, neither model gives a completely satisfactory explanation to the population as a whole; thus, alternative theories have arisen, including tidal disruption events (TDEs). By considering observational constraints on the radio emission of LRDs, we discuss whether TDEs are adequate alternatives solving these high-redshift enigmas. We utilise radio flux density upper limits from LRD stacking analyses, TDE peak radio luminosities, and volumetric density estimates. We find that the characteristic values of flux densities and luminosities allow radio-quiet TDEs as the underlying process of LRDs in any case, while the less common radio-loud TDEs are compatible with the model under special constraints only. Considering other factors, such as volumetric density estimates, delayed and long-term radio flares of TDEs, and cosmological time dilation, TDEs appear to be a plausible explanation for LRDs from the radio point of view.

@article{2025Univ...11..294P, author = {{Perger}, Krisztina and {Fogasy}, Judit and {Frey}, S{\'a}ndor}, title = {{What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?}}, journal = {Universe}, keywords = {little red dots, tidal disruption events, radio continuum, high redshift}, year = {2025}, month = sep, volume = {11}, number = {9}, eid = {294}, pages = {294}, doi = {10.3390/universe11090294}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025Univ...11..294P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {181048372}, lrdkeys = {early universe, jwst, non-agn, radio, theory}, eprint = {2509.03291}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {9} }

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A Confirmed Deficit of Hot and Cold Dust Emission in the Most Luminous Little Red Dots

David J. Setton, Jenny E. Greene, Justin S. Spilker, and 33 more authors

The Astrophysical Journal Letters, Sep 2025

Abs DOI ADS arXiv

Luminous broad H\ensuremathα emission and red rest-optical spectral energy distributions (SEDs) are the hallmark of compact little red dots (LRDs), implying highly attenuated dusty starbursts and/or obscured active galactic nuclei (AGN). However, the lack of observed far-infrared (FIR) emission has proved difficult to reconcile with the implied attenuated luminosity in these models. Here, we utilize deep new Atacama Large Millimeter/submillimeter Array imaging, new and existing JWST/MIRI imaging, and archival Spitzer/Herschel imaging of two of the rest-optically brightest LRDs (z = 3.1 and z = 4.47) to place the strongest constraints on the IR luminosity in LRDs to date. The detections at \ensuremathλ_rest = 1–4 \ensuremathμm imply flat slopes in the rest-IR, ruling out a contribution from hot (T \ensuremath≳ 500 K) dust. Similarly, FIR nondetections rule out any appreciable cold (T \ensuremath≲ 75 K) dust component. Assuming energy balance, these observations are inconsistent with the typical FIR dust emission of dusty starbursts and quasar tori, which usually show a mixture of cold and hot dust. Additionally, our [C II] nondetections rule out typical dusty starbursts. We compute empirical maximum IR SEDs and find that both LRDs must have log(LIR/L\ensuremath⊙)\ensuremath≲12.2 at the 3\ensuremathσ level. These limits are in tension with the predictions of rest-optical spectrophotometric fits, be they galaxy-only, AGN-only, or composite. It is unlikely that LRDs are highly dust-reddened intrinsically blue sources with a dust temperature distribution that conspires to avoid current observing facilities. Rather, we favor an intrinsically redder LRD SED model that alleviates the need for strong dust attenuation.

@article{2025ApJ...991L..10S, author = {{Setton}, David J. and {Greene}, Jenny E. and {Spilker}, Justin S. and {Williams}, Christina C. and {Labb{\'e}}, Ivo and {Ma}, Yilun and {Wang}, Bingjie and {Whitaker}, Katherine E. and {Leja}, Joel and {de Graaff}, Anna and {Alberts}, Stacey and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Brammer}, Gabriel and {Cutler}, Sam E. and {Cleri}, Nikko J. and {Cooper}, Olivia R. and {Dayal}, Pratika and {Fujimoto}, Seiji and {Furtak}, Lukas J. and {Goulding}, Andy D. and {Hirschmann}, Michaela and {Kokorev}, Vasily and {Maseda}, Michael V. and {McConachie}, Ian and {Matthee}, Jorryt and {Miller}, Tim B. and {Naidu}, Rohan P. and {Oesch}, Pascal A. and {Pan}, Richard and {Price}, Sedona H. and {Suess}, Katherine A. and {Weaver}, John R. and {Xiao}, Mengyuan and {Zhang}, Yunchong and {Zitrin}, Adi}, title = {{A Confirmed Deficit of Hot and Cold Dust Emission in the Most Luminous Little Red Dots}}, journal = {\apjl}, keywords = {Active galactic nuclei, High-redshift galaxies, Galaxy evolution, Far infrared astronomy, 16, 734, 594, 529}, year = {2025}, month = sep, volume = {991}, number = {1}, eid = {L10}, pages = {L10}, doi = {10.3847/2041-8213/ade78b}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...991L..10S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, multi-wavelength, non-agn, sed, starburst}, altmetric = {181615848}, eprint = {2503.02059}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {9} }

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NEXUS: A Search for Nuclear Variability with the First Two JWST NIRCam Epochs

Zachary Stone, Yue Shen, Ming-Yang Zhuang, and 10 more authors

arXiv e-prints, Sep 2025

Abs ADS arXiv

The multi-cycle JWST Treasury program NEXUS will obtain cadenced imaging and spectroscopic observations around the North Ecliptic Pole during 2024-2028. Here we report a systematic search for nuclear variability among ∼25 k sources covered by NIRCam (F200W+F444W) imaging using the first two NEXUS epochs separated by 9 months in the observed frame. Difference imaging techniques reach 1σ variability sensitivity of 0.18\raisebox-0.5ex\textasciitildemag (F200W) and 0.15\raisebox-0.5ex\textasciitildemag (F444W) at 28th magnitude (within 0”.2 diameter aperture), improved to 0.01\raisebox-0.5ex\textasciitildemag and 0.02\raisebox-0.5ex\textasciitildemag at 30%). We identify 465 high-confidence variable sources among the parent sample, with 2-epoch flux difference at >3σ from the fiducial variability sensitivity. Essentially all these variable sources are of extragalactic origin based on preliminary photometric classifications, and follow a similar photometric redshift distribution as the parent sample up to z_\rm phot>10. While the majority of these variability candidates are likely normal unobscured AGNs, some of them may be rare nuclear stellar transients and tidal disruption events that await confirmation with spectroscopy and continued photometric monitoring. We also constrain the photometric variability of ten spectroscopically confirmed broad-line Little Red Dots (LRDs) at 3≲z ≲7, and find none of them show detectable variability in either band. We derive stringent 3σ upper limits on the F444W variability of ∼3-10% for these LRDs, with a median value of ∼5%. These constraints imply weak variability in the rest-frame optical continuum of LRDs.

@article{2025arXiv250919585S, author = {{Stone}, Zachary and {Shen}, Yue and {Zhuang}, Ming-Yang and {Hu}, Lei and {Pierel}, Justin and {Li}, Junyao and {Burgasser}, Adam J. and {Greene}, Jenny E. and {Pan}, Zhiwei and {Shapley}, Alice E. and {Sun}, Fengwu and {Venkatraman}, Padmavathi and {Wang}, Feige}, title = {{NEXUS: A Search for Nuclear Variability with the First Two JWST NIRCam Epochs}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.19585}, pages = {arXiv:2509.19585}, archiveprefix = {arXiv}, eprint = {2509.19585}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250919585S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, photometry, spectroscopy, variability}, month_numeric = {9} }

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A remarkable ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a little red dot at z = 3.5

Anna de Graaff, Hans-Walter Rix, Rohan P. Naidu, and 25 more authors

Astronomy & Astrophysics, Sep 2025

Abs DOI ADS arXiv

The origin of the rest-optical emission of compact, red, high-redshift sources known as little red dots (LRDs) poses a major puzzle. If interpreted as starlight, it would imply that LRDs constitute the densest stellar systems in the Universe. However, alternative models suggest active galactic nuclei (AGN) may instead power the rest-optical continuum. Here, we present JWST/NIRSpec, NIRCam, and MIRI observations from the RUBIES and PRIMER programs of The Cliff: a bright LRD at z = 3.55 with an exceptional Balmer break, twice as strong as that of any high- redshift source previously observed. The spectra also reveal broad hydrogen (H\ensuremathα FWHM \ensuremath∼ 1500 km s^‑1) and He I emission, but no significant metal lines. We demonstrate that massive evolved stellar populations cannot explain the observed spectrum, even when considering unusually steep and strong dust attenuation or reasonable variations in the initial mass function. Moreover, the formally best-fit stellar mass and compact size (M_* \ensuremath∼ 10^10.5 M_\ensuremath⊙, r_e \ensuremath∼ 40 pc) would imply densities at which near-monthly stellar collisions might lead to significant X-ray emission. We argue that the Balmer break, emission lines, and H\ensuremathα absorption line are instead most plausibly explained by a black hole star (BH^*) scenario, in which dense gas surrounds a powerful ionising source. In contrast to recently proposed BH^* models of dust-reddened AGN, we show that spectral fits in the rest UV to near-infrared favour an intrinsically redder continuum over strong dust reddening. This may point to a super-Eddington accreting massive black hole or, possibly, the presence of (super)massive stars in a nuclear star cluster. The Cliff is the clearest evidence to date that at least some LRDs are not ultra-dense massive galaxies, and are instead powered by a central ionising source embedded in dense, absorbing gas.

@article{2025A&A...701A.168D, author = {{de Graaff}, Anna and {Rix}, Hans-Walter and {Naidu}, Rohan P. and {Labb{\'e}}, Ivo and {Wang}, Bingjie and {Leja}, Joel and {Matthee}, Jorryt and {Katz}, Harley and {Greene}, Jenny E. and {Hviding}, Raphael E. and {Baggen}, Josephine and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Brammer}, Gabriel and {Dayal}, Pratika and {van Dokkum}, Pieter and {Goulding}, Andy D. and {Hirschmann}, Michaela and {Maseda}, Michael V. and {McConachie}, Ian and {Miller}, Tim B. and {Nelson}, Erica and {Oesch}, Pascal A. and {Setton}, David J. and {Shivaei}, Irene and {Weibel}, Andrea and {Whitaker}, Katherine E. and {Williams}, Christina C.}, title = {{A remarkable ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a little red dot at z = 3.5}}, journal = {\aap}, keywords = {galaxies: active, galaxies: evolution, galaxies: kinematics and dynamics, galaxies: stellar content}, year = {2025}, month = sep, volume = {701}, eid = {A168}, pages = {A168}, doi = {10.1051/0004-6361/202554681}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...701A.168D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {181353895}, lrdkeys = {emission lines, jwst, non-agn, sed, spectroscopy}, eprint = {2503.16600}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {9} }

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XMM-Newton Conclusively Identifies an Active Galactic Nucleus in a Green Pea Galaxy

Peter G. Boorman, Jiřı́ Svoboda, Daniel Stern, and 23 more authors

The Astrophysical Journal, Aug 2025

Abs DOI ADS arXiv

Green Pea galaxies are a class of compact, low-mass, low-metallicity star-forming galaxies in the relatively local Universe. They are believed to be analogs of high-redshift galaxies that reionized the Universe, and, indeed, the James Webb Space Telescope (JWST) is now uncovering such populations at record redshifts. Intriguingly, JWST finds evidence suggestive of active galactic nuclei (AGN) in many of these distant galaxies, including the elusive Little Red Dots, which broadly lack any detectable X-ray counterparts. Intuitively, one would expect to detect an AGN in their low-redshift analogs with X-rays, yet no study to date has conclusively identified an X-ray AGN within a Green Pea galaxy. Here we present the deepest X-ray campaign of a Green Pea galaxy performed to date, obtained with the goal of discerning the presence of a (potentially low-luminosity) AGN. The target—SDSS J082247.66+224144.0 (hereafter J0822+2241)—was previously found to display a comparable X-ray spectral shape to more local AGN (\ensuremathΓ \ensuremath∼ 2) and a high luminosity (L_2‑10 keV \ensuremath∼ 10^42 erg s^‑1). We show that over 6.2 yr (rest frame) the 2–10 keV luminosity of J0822+2241 is constant, whereas the soft 0.5–2 keV flux has decreased significantly by \ensuremath∼60%. We discuss possible scenarios to explain the X-ray properties of J0822+2241, finding transient low column density obscuration surrounding an AGN to be the only plausible scenario. J0822+2241 thus provides further evidence that low-luminosity AGN activity could have contributed to the epoch of reionization and that local analogs are useful to derive a complete multiwavelength picture of black hole growth in high-redshift, low-luminosity AGNs. *Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

@article{2025ApJ...988..157B, author = {{Boorman}, Peter G. and {Svoboda}, Ji{\v{r}}{\'\i} and {Stern}, Daniel and {Lehmer}, Bret D. and {Borkar}, Abhijeet and {Brightman}, Murray and {Earnshaw}, Hannah P. and {Harrison}, Fiona A. and {Kouroumpatzakis}, Konstantinos and {Adamcov{\'a}}, Barbora and {Assef}, Roberto J. and {Ehle}, Matthias and {Grefenstette}, Brian and {Grossov{\'a}}, Romana and {Gupta}, Maitrayee and {Kammoun}, Elias and {Kawamuro}, Taiki and {Marcotulli}, Lea and {Miku{\v{s}}incov{\'a}}, Romana and {Middleton}, Matthew J. and {Nathan}, Edward and {Piotrowska}, Joanna M. and {Somalwar}, Jean J. and {Torres-Alb{\`a}}, N{\'u}ria and {Walton}, Dominic J. and {Weisz}, Daniel R.}, title = {{XMM-Newton Conclusively Identifies an Active Galactic Nucleus in a Green Pea Galaxy}}, journal = {\apj}, keywords = {Starburst galaxies, Active galaxies, Compact galaxies, X-ray active galactic nuclei, 1570, 17, 285, 2035}, year = {2025}, month = aug, volume = {988}, number = {2}, eid = {157}, pages = {157}, doi = {10.3847/1538-4357/add727}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...988..157B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, local counterpart, multi-wavelength, variability, x-ray}, eprint = {2505.08885}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {8} }

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Lonely Little Red Dots: Challenges to the Active Galactic Nucleus Nature of Little Red Dots through Their Clustering and Spectral Energy Distributions

Marı́a Carranza-Escudero, Christopher J. Conselice, Nathan Adams, and 31 more authors

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

Observations with the James Webb Space Telescope reveal a previously unseen population of compact red objects, known as “little red dots” (LRDs). We study a new photometrically selected sample of 124 LRDs in the redshift range z \ensuremath∼ 3–10 selected from Near Infrared Camera coverage of the Cosmic Evolution Early Release Science Survey (CEERS), North Ecliptic Pole Time Domain Field (NEP-TDF), James Webb Space Telescope Advanced Deep Extragalactic Survey (JADES), and JEMS. For JADES, the NEP-TDF, and CEERS, we compare spectral energy distribution (SED) models with and without active galactic nucleus (AGN) components and analyze the impact of an AGN component on the goodness of fit using the Bayesian information criterion (BIC). We find that while the \ensuremathχ^2 of the majority of models containing AGN components is improved compared to models without AGN components, we show that the BIC suggests that models without AGN are a more appropriate fit to LRD SEDs, especially when MIRI data are available. We also measure LRD clustering in the CEERS field, JADES field, and NEP-TDF, where we compare the spatial distribution of LRDs and galaxies with Kolmogorov–Smirnov tests of equality of distribution. We find that the neighbourhood of LRDs tends to be less dense compared to galaxies at all selections and masses and at similar redshifts. We further measure upper limit estimates for the halo masses of LRDs using abundance matching. While the population of LRDs could be a mixture of several different inherent populations, as a whole, it does appear that these systems are mostly hosting compact galaxies or star clusters in formation.

@article{2025ApJ...989L..50C, author = {{Carranza-Escudero}, Mar{\'\i}a and {Conselice}, Christopher J. and {Adams}, Nathan and {Harvey}, Thomas and {Austin}, Duncan and {Behroozi}, Peter and {Ferreira}, Leonardo and {Ormerod}, Katherine and {Duan}, Qiao and {Trussler}, James and {Li}, Qiong and {Westcott}, Lewi and {Windhorst}, Rogier A. and {Coe}, Dan and {Cohen}, Seth H. and {Cheng}, Cheng and {Driver}, Simon P. and {Frye}, Brenda and {Furtak}, Lukas J. and {Grogin}, Norman A. and {Hathi}, Nimish P. and {Jansen}, Rolf A. and {Koekemoer}, Anton M. and {Marshall}, Madeline A. and {O'Brien}, Rosalia and {Pirzkal}, Norbert and {Polletta}, Maria and {Robotham}, Aaron and {Rutkowski}, Michael J. and {Summers}, Jake and {Wilkins}, Stephen M. and {Willmer}, Christopher N. A. and {Yan}, Haojing and {Zitrin}, Adi}, title = {{Lonely Little Red Dots: Challenges to the Active Galactic Nucleus Nature of Little Red Dots through Their Clustering and Spectral Energy Distributions}}, journal = {\apjl}, keywords = {Galaxies, AGN host galaxies, Active galactic nuclei, High-redshift galaxies, James Webb Space Telescope, 573, 2017, 16, 734, 2291}, year = {2025}, month = aug, volume = {989}, number = {2}, eid = {L50}, pages = {L50}, doi = {10.3847/2041-8213/adf73d}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989L..50C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {180488661}, lrdkeys = {clustering, jwst, non-agn, photometry, sed}, eprint = {2506.04004}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {8} }

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The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots

Chang-Hao Chen, Luis C. Ho, Ruancun Li, and 1 more author

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

A significant fraction of little red dots (LRDs) exhibit nearby extended emission of unknown origin. If physically associated with the LRD, this component may trace stellar emission from an off- center host galaxy, neighboring companions, or nebular gas illuminated by the active nucleus. We investigate the detailed spectral energy distribution (SED) of the extended emission near four LRDs in the JWST UNCOVER and MegaScience surveys. We accurately decompose the extended emission from the dominant point source by simultaneously fitting the images in eight broadband and nine medium-band filters. After considering both the results from photometric redshift fitting and the probability of galaxies at different redshifts overlapping, we confirm that the off-center blobs in three sources are physically associated with the LRDs, with two of them showing strong [O III] \ensuremathλ\ensuremathλ4959, 5007 emission captured by the medium-band filters. While the SEDs of all three blobs can be modeled assuming star-forming galaxies with stellar mass \ensuremath∼10^8 M_\ensuremath⊙, the exceptionally strong [O III] emission of two sources is best interpreted as pure nebular emission from low-density (n < 10 cm^‑3), low-metallicity (Z \ensuremath≈ 0.05‑1 Z_\ensuremath⊙) gas photoionized by the ultraviolet radiation from the nearby LRD. Adopting LRD halo masses constrained by clustering measurements and theoretical considerations, we estimate a typical baryonic halo mass accretion rate of \ensuremath∼2‑9 M_\ensuremath⊙ yr^‑1. If the halo accretion rate is sustained to z = 4 and stars form with an efficiency of 10%, the accreted gas would build a galaxy with stellar mass \ensuremath∼10^9 M_\ensuremath⊙, potentially rendering them spatially resolved at lower redshift.

@article{2025ApJ...989L..12C, author = {{Chen}, Chang-Hao and {Ho}, Luis C. and {Li}, Ruancun and {Inayoshi}, Kohei}, title = {{The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots}}, journal = {\apjl}, keywords = {Early universe, High-redshift galaxies, Active galactic nuclei, AGN host galaxies, 435, 734, 16, 2017, Astrophysics of Galaxies}, year = {2025}, month = aug, volume = {989}, number = {1}, eid = {L12}, pages = {L12}, doi = {10.3847/2041-8213/adee0a}, archiveprefix = {arXiv}, eprint = {2505.03183}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989L..12C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, host galaxy, jwst, photometry, sed}, month_numeric = {8} }

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Evidence for Evolutionary Pathway-dependent Black Hole Scaling Relations

Jonathan H. Cohn, Emmanuel Durodola, Quinn O. Casey, and 2 more authors

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

Recent observations have identified an abundance of high-redshift active galactic nuclei (AGN) with overmassive supermassive black holes (BHs) compared to the local BH mass‑total stellar mass (M_BH–M_\ensuremath⋆) relation for AGN. High-z M_BH measurements are critical for probing growth histories of BHs and their host galaxies, including BH seeding and evolution of the M_BH–M_\ensuremath⋆ relation. However, BH masses in high-z AGN are generally estimated from single-epoch measurements, which carry large systematic uncertainties. More reliable M_BH detection methods like dynamical measurements are currently only possible in the local Universe or with strongly lensed systems. Fortunately, new dynamical M_BH measurements in a sample of six local galaxies identified as likely relics of common quiescent red nugget galaxies at cosmic noon, as well as a z \ensuremath∼ 2 lensed red nugget, present a complementary probe of high-z relations. We compare the z \ensuremath∼ 2 red nugget and relic BHs to recent results for 4 < z < 11 AGN, quasi-stellar objects, and little red dots. Intriguingly, the z \ensuremath∼ 2 galaxy and local relics all lie on both the local M_BH–M_\ensuremath⋆ relation for bulges and the 4 < z < 7 M_BH–M_\ensuremath⋆ AGN relation, although high-z AGN remain overmassive compared to both local relations. We conclude it is unlikely that a uniform M_BH–M_\ensuremath⋆ redshift evolution applies to all galaxies. Since total M_\ensuremath⋆ is affected by growth processes that may not drive BH growth, different evolutionary pathways must be carefully considered when building BH scaling relations.

@article{2025ApJ...988L..61C, author = {{Cohn}, Jonathan H. and {Durodola}, Emmanuel and {Casey}, Quinn O. and {Lambrides}, Erini and {Hickox}, Ryan C.}, title = {{Evidence for Evolutionary Pathway-dependent Black Hole Scaling Relations}}, journal = {\apjl}, keywords = {High-redshift galaxies, Active galaxies, Early-type galaxies, Active galactic nuclei, Supermassive black holes, Scaling relations, Galaxy evolution, 734, 17, 429, 16, 1663, 2031, 594}, year = {2025}, month = aug, volume = {988}, number = {2}, eid = {L61}, pages = {L61}, doi = {10.3847/2041-8213/adf100}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...988L..61C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, local counterpart, spectroscopy}, eprint = {2504.00172}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {8} }

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MIDIS: MIRI Uncovers Virgil, the First Little Red Dot with Clear Detection of Its Host Galaxy at z ≃ 6.6

Edoardo Iani, Pierluigi Rinaldi, Karina I. Caputi, and 26 more authors

The Astrophysical Journal, Aug 2025

Abs DOI ADS arXiv

We present Virgil, a Mid-Infrared Instrument (MIRI) extremely red object detected with the F1000W filter as part of the MIRI Deep Imaging Survey observations of the Hubble Ultra Deep Field. Virgil is an Ly\ensuremathα emitter (LAE) at z_spec = 6.6312 \ensuremath\pm 0.0019 (from the Very Large Telescope/MUSE) with a rest-frame UV-to-optical spectral energy distribution (SED) typical of LAEs at similar redshifts. However, MIRI observations reveal an unexpected extremely red color at rest- frame near-infrared (NIR) wavelengths, F444W ‑ F1000W = 2.33 \ensuremath\pm 0.06. Such a steep rise in the NIR, completely missed without MIRI imaging, is poorly reproduced by models including only stellar populations and hints toward the presence of an active galactic nucleus, although alternative explanations such as extreme dust obscuration and strong nebular continuum and emission lines contribution due to young stellar ages cannot be completely ruled out. According to the shape of its overall SED, Virgil belongs to the recently discovered population of little red dots but displays an extended rest- frame UV-optical wavelength morphology following a 2D-Sérsic profile with an average index of n=0.93‑0.31+0.85 and re=0.49‑0.11+0.05 pkpc. Only at MIRI wavelengths, Virgil is unresolved due to the coarser point-spread function. This discovery demonstrates the crucial importance of deep MIRI surveys to reveal the true nature and properties of high-z galaxies that otherwise would be misinterpreted and raises the question of how common Virgil-like objects could be in the early Universe.

@article{2025ApJ...989..160I, author = {{Iani}, Edoardo and {Rinaldi}, Pierluigi and {Caputi}, Karina I. and {Annunziatella}, Marianna and {Langeroodi}, Danial and {Melinder}, Jens and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {{\'A}lvarez-M{\'a}rquez}, Javier and {Boogaard}, Leindert A. and {Bosman}, Sarah E. I. and {Costantin}, Luca and {Moutard}, Thibaud and {Colina}, Luis and {{\"O}stlin}, G{\"o}ran and {Greve}, Thomas R. and {Wright}, Gillian and {Alonso-Herrero}, Almudena and {Bik}, Arjan and {Gillman}, Steven and {Crespo G{\'o}mez}, Alejandro and {Hjorth}, Jens and {Kendrew}, Sarah and {Labiano}, Alvaro and {Pye}, John P. and {Tikkanen}, Tuomo V. and {Walter}, Fabian and {G{\"u}del}, Manuel and {Henning}, Thomas and {van der Werf}, Paul P.}, title = {{MIDIS: MIRI Uncovers Virgil, the First Little Red Dot with Clear Detection of Its Host Galaxy at z ≃ 6.6}}, journal = {\apj}, keywords = {Galaxy formation, Galaxy evolution, High-redshift galaxies, Stellar populations, Active galactic nuclei, Galaxy ages, James Webb Space Telescope, 595, 594, 734, 1622, 16, 576, 2291, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = aug, volume = {989}, number = {2}, eid = {160}, pages = {160}, doi = {10.3847/1538-4357/ade5a6}, archiveprefix = {arXiv}, eprint = {2406.18207}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989..160I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, morphology, sed}, month_numeric = {8} }

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Cosmic Outliers: Low-spin Halos Explain the Abundance, Compactness, and Redshift Evolution of the Little Red Dots

Fabio Pacucci and Abraham Loeb

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

The little red dots (LRDs) are high-redshift galaxies uncovered by JWST, characterized by small effective radii (R_eff \ensuremath∼ 80–300 pc), number densities intermediate between typical galaxies and quasars, and a redshift distribution peaked at z \ensuremath∼ 5. We present a theoretical model in which the LRDs descend from dark matter halos in the extreme low-spin tail of the angular momentum distribution. Within this framework, we explain their three key observational signatures: (i) abundance, (ii) compactness, and (iii) redshift distribution. Our model focuses on observed, not modeled, properties; it is thus independent of whether they are powered primarily by a black hole or stars. We find that the assumption that the prototypical LRD at z \ensuremath∼ 5 originates from halos in the lowest \ensuremath∼1% of the spin distribution is sufficient to reproduce both their observed number densities and physical sizes. The redshift evolution of their observability is driven by the interplay between the evolving compact disk fraction and cosmological surface brightness dimming. This effect leads to a well-defined “LRD era” at 4 8, they are common but faint. Finally, we test the predicted redshift trend against observational data, finding excellent agreement. Additional observational support comes from their excess small-scale clustering and spectral signatures of extreme core densities, both of which are expected outcomes of galaxy formation in low-spin halos. These findings suggest that the LRDs are not a fundamentally distinct population but the natural manifestation of galaxies forming in the rarest, lowest angular momentum environments.

@article{2025ApJ...989L..19P, author = {{Pacucci}, Fabio and {Loeb}, Abraham}, title = {{Cosmic Outliers: Low-spin Halos Explain the Abundance, Compactness, and Redshift Evolution of the Little Red Dots}}, journal = {\apjl}, keywords = {Early universe, Galaxies, Cosmology, Galaxy evolution, Active galaxies, 435, 573, 343, 594, 17, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2025}, month = aug, volume = {989}, number = {2}, eid = {L19}, pages = {L19}, doi = {10.3847/2041-8213/ade871}, archiveprefix = {arXiv}, eprint = {2506.03244}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989L..19P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {180223611}, lrdkeys = {clustering, early universe, jwst, morphology, theory}, month_numeric = {8} }

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Chandra Rules Out Super-Eddington Accretion Models for Little Red Dots

Andrea Sacchi and Ákos Bogdán

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

One of the most puzzling discoveries by JWST is the population of high- redshift, red, and compact galaxies dubbed little red dots (LRDs). Based on broad-line diagnostics, these galaxies have been argued to host accreting 10^7–10^8 M_\ensuremath⊙ supermassive black holes (SMBHs), a claim with crucial consequences for our understanding of how the first black holes form and grow over cosmic time. A key feature of LRDs is their extreme X-ray weakness: analyses of individual and stacked sources have yielded nondetections or only tentative, inconclusive X-ray signals, except for a handful of individual cases. Although high obscuration is the most straightforward way to explain the X-ray weakness of LRDs, JWST rest-frame optical/UV spectra initially argued against the presence of Compton-thick gas clouds. Instead, several authors have proposed that LRDs are intrinsically X-ray weak due to super-Eddington accretion rates. In this work, we observationally test these tailored models by stacking X-ray data for 55 LRDs in the Chandra Deep Field South, accumulating a total exposure time of nearly 400 Ms. Despite reaching unprecedented X-ray depths, our stack still yields a nondetection. The corresponding upper limits are deep enough to rule out current super-Eddington accretion models and are compatible only with extremely high levels of obscuration (N_H \ensuremath≳ 10^25 cm^‑2). To explain the X-ray weakness of LRDs, we therefore speculate that the SMBHs in these systems are neither as massive nor as luminous as currently believed.

@article{2025ApJ...989L..30S, author = {{Sacchi}, Andrea and {Bogd{\'a}n}, {\'A}kos}, title = {{Chandra Rules Out Super-Eddington Accretion Models for Little Red Dots}}, journal = {\apjl}, keywords = {Accretion, Supermassive black holes, James Webb Space Telescope, Active galactic nuclei, X-ray active galactic nuclei, 14, 1663, 2291, 16, 2035, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2025}, month = aug, volume = {989}, number = {2}, eid = {L30}, pages = {L30}, doi = {10.3847/2041-8213/adf5c8}, archiveprefix = {arXiv}, eprint = {2505.09669}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989L..30S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, early universe, jwst, x-ray}, month_numeric = {8} }

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CAPERS-LRD-z9: A Gas-enshrouded Little Red Dot Hosting a Broad-line Active Galactic Nucleus at z = 9.288

Anthony J. Taylor, Vasily Kokorev, Dale D. Kocevski, and 49 more authors

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

We present CAPERS-LRD-z9, a little red dot (LRD) that we confirm to be a z = 9.288 broad-line active galactic nucleus (BLAGN). First identified as a high-redshift LRD candidate from PRIMER NIRCam photometry, follow-up NIRSpec/PRISM spectroscopy of CAPERS- LRD-z9 from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS) has revealed a broad 3500 km s^‑1 full width at half-maximum H\ensuremathβ emission line and narrow [O III] \ensuremathλ\ensuremathλ4959, 5007 lines, indicative of a BLAGN. Based on the broad H\ensuremathβ line, we compute a canonical black hole mass of log(MBH/M\ensuremath⊙)=7.58\ensuremath\pm0.15, although full consideration of systematic uncertainties yields a conservative range of 6.65log(MBH/M\ensuremath⊙)8.50. These observations suggest that either a massive black hole seed or a lighter stellar remnant seed undergoing periods of super- Eddington accretion is necessary to grow such a massive black hole in \ensuremath≲500 Myr of cosmic time. CAPERS- LRD-z9 exhibits a strong Balmer break, consistent with a central AGN surrounded by dense (\ensuremath∼10^10 cm^‑3) neutral gas. We model CAPERS-LRD-z9 using Cloudy to fit the emission redward of the Balmer break with a dense-gas- enshrouded AGN and bagpipes to fit the rest-ultraviolet emission as a host-galaxy stellar population. This upper limit on the stellar mass of the host galaxy (5% (although systematic uncertainties on the black hole mass prevent strong conclusions). However, the shape of the UV continuum differs from typical high-redshift star-forming galaxies, indicating that this UV emission may also be of AGN origin; hence, the true stellar mass of the host may be still lower.

@article{2025ApJ...989L...7T, author = {{Taylor}, Anthony J. and {Kokorev}, Vasily and {Kocevski}, Dale D. and {Akins}, Hollis B. and {Cullen}, Fergus and {Dickinson}, Mark and {Finkelstein}, Steven L. and {Arrabal Haro}, Pablo and {Bromm}, Volker and {Giavalisco}, Mauro and {Inayoshi}, Kohei and {Juneau}, St{\'e}phanie and {Leung}, Gene C. K. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Somerville}, Rachel S. and {Trump}, Jonathan R. and {Amor{\'\i}n}, Ricardo O. and {Barro}, Guillermo and {Burgarella}, Denis and {Brooks}, Madisyn and {Carnall}, Adam C. and {Casey}, Caitlin M. and {Cheng}, Yingjie and {Chisholm}, John and {Chworowsky}, Katherine and {Davis}, Kelcey and {Donnan}, Callum T. and {Dunlop}, James S. and {Ellis}, Richard S. and {Fern{\'a}ndez}, Vital and {Fujimoto}, Seiji and {Grogin}, Norman A. and {Gupta}, Ansh R. and {Hathi}, Nimish P. and {Jung}, Intae and {Hirschmann}, Michaela and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Larson}, Rebecca L. and {Leung}, Ho-Hin and {Llerena}, Mario and {Lucas}, Ray A. and {McLeod}, Derek J. and {McLure}, Ross and {Napolitano}, Lorenzo and {Papovich}, Casey and {Stanton}, Thomas M. and {Tripodi}, Roberta and {Wang}, Xin and {Wilkins}, Stephen M. and {Yung}, L. Y. Aaron and {Zavala}, Jorge A.}, title = {{CAPERS-LRD-z9: A Gas-enshrouded Little Red Dot Hosting a Broad-line Active Galactic Nucleus at z = 9.288}}, journal = {\apjl}, keywords = {James Webb Space Telescope, Active galactic nuclei, AGN host galaxies, Supermassive black holes, 2291, 16, 2017, 1663}, year = {2025}, month = aug, volume = {989}, number = {1}, eid = {L7}, pages = {L7}, doi = {10.3847/2041-8213/ade789}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989L...7T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {180066630}, lrdkeys = {black hole mass, emission lines, host galaxy, jwst, spectroscopy}, eprint = {2505.04609}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {8} }

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No [C II] or dust detection in two Little Red Dots at z_spec> 7

Mengyuan Xiao, Pascal A. Oesch, Longji Bing, and 30 more authors

Astronomy & Astrophysics, Aug 2025

Abs DOI ADS arXiv

Little Red Dots (LRDs) are compact, point-like sources characterized by their red color and broad Balmer lines; it is a matter of debate whether they are dominated by active galactic nuclei (AGNs) or dusty star-forming galaxies (DSFGs). Here we report two LRDs (ID9094 and ID2756) at z_spec > 7 recently discovered in the JWST FRESCO GOODS-North field. Both satisfy the “v-shaped” color and compactness criteria for LRDs and are identified as Type-I AGN candidates based on their broad H\ensuremathβ emission lines (full width at half maximum: 2280 \ensuremath\pm 490 km s^‑1 for ID9094 and 1070 \ensuremath\pm 240 km s^‑1 for ID2756) and narrow [O III] lines (≃300 ‑ 400 km s^‑1). To investigate their nature, we conducted deep NOEMA follow-up observations targeting the [C II] 158 \ensuremathμm emission line and the 1.3 mm dust continuum. We do not detect [C II] or 1.3 mm continuum emission for either source. If the two LRDs were DSFGs, we would expect significant detections: > 16\ensuremathσ for [C II] and > 3\ensuremathσ for the 1.3 mm continuum of ID9094, and > 5\ensuremathσ for the [C II] of ID2756. Using the 3\ensuremathσ upper limits of [C II] and 1.3 mm, we performed two analyses: (1) UV-to-far-infrared spectral energy distribution fitting with and without AGN components, and (2) comparison of their properties with the L_[C II]–SFR_tot empirical relation. Both analyses are consistent with a scenario in which AGN activity contributes to the observed properties, though a dusty star-forming origin cannot be fully ruled out. Our results highlight the importance of far-infrared observations for studying LRDs, a regime that remains largely unexplored.

@article{2025A&A...700A.231X, author = {{Xiao}, Mengyuan and {Oesch}, Pascal A. and {Bing}, Longji and {Elbaz}, David and {Matthee}, Jorryt and {Fudamoto}, Yoshinobu and {Fujimoto}, Seiji and {Marques-Chaves}, Rui and {Williams}, Christina C. and {Dessauges-Zavadsky}, Miroslava and {Valentino}, Francesco and {Brammer}, Gabriel and {Covelo-Paz}, Alba and {Daddi}, Emanuele and {Fynbo}, Johan P. U. and {Gillman}, Steven and {Ginolfi}, Michele and {Giovinazzo}, Emma and {Greene}, Jenny E. and {Gu}, Qiusheng and {Illingworth}, Garth and {Inayoshi}, Kohei and {Kokorev}, Vasily and {Meyer}, Romain A. and {Naidu}, Rohan P. and {Reddy}, Naveen A. and {Schaerer}, Daniel and {Shapley}, Alice and {Stefanon}, Mauro and {Steinhardt}, Charles L. and {Setton}, David J. and {Vestergaard}, Marianne and {Wang}, Tao}, title = {{No [C II] or dust detection in two Little Red Dots at z$\_{spec}$> 7}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift, galaxies: photometry, galaxies: star formation, submillimeter: galaxies, Astrophysics of Galaxies}, year = {2025}, month = aug, volume = {700}, eid = {A231}, pages = {A231}, doi = {10.1051/0004-6361/202554361}, archiveprefix = {arXiv}, eprint = {2503.01945}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...700A.231X}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, non-agn, sed}, altmetric = {174878459}, month_numeric = {8} }

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Little Red reionization factories

Fan Zhang

arXiv e-prints, Aug 2025

Abs ADS arXiv

In this note, we suggest the possibility that an elucidation of the nature of the numerous Little Red Dots (LRDs) at high redshifts, may facilitate the resolution of another concurrent cosmic puzzle, namely reionization. Specifically, it is hypothesized that intergalactic HI gas is compelled by the tidal field associated with a growing gravitational entropy, in the form of gas streams, into colliding at the LRD sites. The resulting shock heating and compression encourage starburst activities, which subsequently photo-ionize the gas into HII, that in turn shines into the rest-optical via bremsstrahlung radiation within the minimal-timescale-cutoff (i.e., red) regime, before escaping back into the intergalactic space, propelled by the newly fusion-injected energy.

@article{2025arXiv250813541Z, author = {{Zhang}, Fan}, title = {{Little Red reionization factories}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.13541}, pages = {arXiv:2508.13541}, archiveprefix = {arXiv}, eprint = {2508.13541}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250813541Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, non-agn, spectroscopy, starburst, theory}, month_numeric = {8} }

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Early universe’s ‘little red dots’ may be black hole stars

Daniel Clery

Science, Jul 2025

Abs DOI ADS

Puzzling objects spotted by NASA’s JWST telescope come into focus

@article{2025Sci...389..438C, author = {{Clery}, Daniel}, title = {{Early universe{\textquoteright}s {\textquoteleft}little red dots{\textquoteright} may be black hole stars}}, journal = {Science}, keywords = {Astronomy}, year = {2025}, month = jul, volume = {389}, number = {6759}, pages = {438-439}, doi = {10.1126/science.aeb0427}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025Sci...389..438C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {180307240}, lrdkeys = {black hole mass, early universe, jwst, non-agn, theory}, month_numeric = {7} }

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Not-quite-primordial black holes seeded by cosmic string loops

Bryce Cyr

arXiv e-prints, Jul 2025

Abs ADS arXiv

Cosmic strings appear in many well-motivated extensions to the standard model of particle physics. If they exist, an abundant population of compact objects known as cosmic string loops permeate the Universe at all times, providing a secondary source of density perturbations that are large amplitude and non-gaussian in nature. In general, these loops are not stationary in the rest frame of the dark matter, thus their relative velocities will typically seed both spherical and filamentary overdensities in the matter era. Building upon previous work, we provide an improved framework to compute the complete halo mass function for these string seeded overdensities, valid for any loop velocity distribution. Using this mass function, we also compute the subset of halos capable of undergoing a direct collapse, forming a population of black holes with initial mass 10^4-5 \,M_⊙ at high redshifts. Interestingly, for reasonable values of the string parameters, one can reproduce the abundance of “Little Red Dots” as inferred by JWST.

@article{2025arXiv250717833C, author = {{Cyr}, Bryce}, title = {{Not-quite-primordial black holes seeded by cosmic string loops}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology}, year = {2025}, month = jul, eid = {arXiv:2507.17833}, pages = {arXiv:2507.17833}, archiveprefix = {arXiv}, eprint = {2507.17833}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250717833C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, non-agn, theory}, month_numeric = {7} }

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Little Red Dots as the Very First Activity of Black Hole Growth

Kohei Inayoshi

The Astrophysical Journal Letters, Jul 2025

Abs DOI ADS arXiv

The James Webb Space Telescope has detected massive black holes (BHs) with masses of \ensuremath∼10^6‑8 M_\ensuremath⊙ within the first billion years of the Universe. One of the remarkable findings is the identification of “little red dots” (LRDs), a unique class of active galactic nuclei (AGNs) with distinct characteristics representing a key phase in the formation and growth of early BHs. Here, we analyze the occurrence rate of LRDs, which emerge around redshifts z \ensuremath∼ 6–8 and sharply decline at z < 4. We find that this trend follows a log-normal distribution, commonly observed in phenomena driven by stochastic and random factors. We propose a hypothesis that the first one or two AGN events associated with newly formed seed BHs are observed as LRDs, and their unique features fade in the subsequent episodes. This naturally explains the cosmic evolution of AGN abundance over 0 < z < 5, which follows \ensuremath∝(1 + z)^‑5/2 due to the cumulative effect of recurring AGN activity. The unique characteristics of LRDs are likely linked to the dense gas environments around the seed BHs, which create strong absorption features in the broad-line emission and enable super-Eddington accretion bursts, ultimately yielding the observed overmassive nature of BHs compared to the local relationship. An analytical expression for the redshift evolution of LRD abundance is provided for direct comparison with future observational constraints.

@article{2025ApJ...988L..22I, author = {{Inayoshi}, Kohei}, title = {{Little Red Dots as the Very First Activity of Black Hole Growth}}, journal = {\apjl}, keywords = {Galaxy formation, High-redshift galaxies, Quasars, Supermassive black holes, 595, 734, 1319, 1663}, year = {2025}, month = jul, volume = {988}, number = {1}, eid = {L22}, pages = {L22}, doi = {10.3847/2041-8213/adea66}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...988L..22I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, theory}, eprint = {2503.05537}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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Joint Survey Processing. III. Compact Oddballs in the COSMOS Field—Little Red Dots and Transients

Yu-Heng Lin, Andreas L. Faisst, Ranga-Ram Chary, and 7 more authors

The Astrophysical Journal, Jul 2025

Abs DOI ADS arXiv

We present the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) G800L grism spectroscopy observation of the faint active galactic nuclei (AGN) candidates in the Cosmic Evolution Survey field at redshift of 6 selected by the point-source morphology and the photometry drop-off at 8000 Å. Among the sample of seven objects, only one is detected by multiple bands and has a similar shape of spectral energy distribution as the so-called “little red dots” of James Webb Space Telescope (JWST)–selected AGN candidates, but our object is 3 mag brighter than the JWST sample. We draw the upper limit of the AGN luminosity function \ensuremathΦ = 1.1 \texttimes 10^‑7 Mpc^3 mag^‑1 for M_UV = ‑21 at redshift of 6. The rest of the sample shows inconsistent flux density when comparing magnitudes of HST ACS F814W to the Subaru i-band and z-band magnitudes combined. The HST ACS G800L grism observation shows that this inconsistency cannot be created from an emission line. Therefore, we speculate that these objects are transients with the light-curve decay timescale of at most 6 yr in the observed frame.

@article{2025ApJ...987...49L, author = {{Lin}, Yu-Heng and {Faisst}, Andreas L. and {Chary}, Ranga-Ram and {Koekemoer}, Anton M. and {Masiero}, Joseph and {Masters}, Daniel and {Mehta}, Vihang and {Teplitz}, Harry I. and {Walth}, Gregory L. and {Weaver}, John R.}, title = {{Joint Survey Processing. III. Compact Oddballs in the COSMOS Field{\textemdash}Little Red Dots and Transients}}, journal = {\apj}, keywords = {Galaxy photometry, High-redshift galaxies, 611, 734}, year = {2025}, month = jul, volume = {987}, number = {1}, eid = {49}, pages = {49}, doi = {10.3847/1538-4357/add7d9}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...987...49L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {non-agn, photometry, sed, spectroscopy, variability}, eprint = {2504.07196}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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SHELLQs. Bridging the Gap: JWST Unveils Obscured Quasars in the Most Luminous Galaxies at z > 6

Yoshiki Matsuoka, Masafusa Onoue, Kazushi Iwasawa, and 17 more authors

The Astrophysical Journal, Jul 2025

Abs DOI ADS arXiv

The unprecedented sensitivity of the James Webb Space Telescope (JWST) has uncovered a surprisingly abundant population of mildly obscured, low-luminosity active galactic nuclei (AGNs) in the epoch of reionization (EoR). However, the link between these objects and classical unobscured quasars remains a mystery. Here we report the discovery of obscured quasars hosted by the most luminous galaxies at z > 6, possibly bridging the gap between the two AGN populations. The 13 objects presented here were originally selected from a rest-frame ultraviolet (UV) imaging survey over >1000 deg^2, and were known to have luminous (>10^43 erg s^‑1) Ly\ensuremathα emission. With JWST/NIRSpec follow-up observations, we found that 7 out of 11 objects with narrow Ly\ensuremathα exhibit a broad component in H I Balmer lines and He I lines, but not in [O III] and other forbidden lines. Mild dust obscuration (0 < A_V < 3) is inferred from the Balmer decrements. The estimated intrinsic luminosities suggest that our broad-line (BL) objects are the long-sought UV-obscured counterparts of luminous quasars in the EoR. They host supermassive black holes (SMBHs) with masses 10^7.8‑9.1M_\ensuremath⊙, undergoing sub- Eddington to Eddington accretion. Most of the BL objects are spatially unresolved and are close to “little red dots” with their blue rest-UV and red rest-optical colors. We estimate the AGN number density among similarly luminous Ly\ensuremathα emitters to be larger than 2 \texttimes 10^‑8 Mpc^‑3. This density is comparable to that of classical quasars with similar continuum luminosities, suggesting that a substantial fraction of active SMBHs are obscured in the EoR and have been overlooked in past rest-UV surveys.

@article{2025ApJ...988...57M, author = {{Matsuoka}, Yoshiki and {Onoue}, Masafusa and {Iwasawa}, Kazushi and {Aoki}, Kentaro and {Strauss}, Michael A. and {Silverman}, John D. and {Ding}, Xuheng and {Phillips}, Camryn L. and {Akiyama}, Masayuki and {Arita}, Junya and {Imanishi}, Masatoshi and {Izumi}, Takuma and {Kashikawa}, Nobunari and {Kawaguchi}, Toshihiro and {Kikuta}, Satoshi and {Kohno}, Kotaro and {Lee}, Chien-Hsiu and {Nagao}, Tohru and {Takahashi}, Ayumi and {Toba}, Yoshiki}, title = {{SHELLQs. Bridging the Gap: JWST Unveils Obscured Quasars in the Most Luminous Galaxies at z > 6}}, journal = {\apj}, keywords = {Supermassive black holes, Quasars, High-redshift galaxies, Reionization, 1663, 1319, 734, 1383}, year = {2025}, month = jul, volume = {988}, number = {1}, eid = {57}, pages = {57}, doi = {10.3847/1538-4357/addf4e}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...988...57M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, early universe, emission lines, jwst}, eprint = {2505.04825}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, altmetric = {181221542}, month_numeric = {7} }

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Quasar identifications from the slitless spectra: a test from 3D-HST

Yuxuan Pang, Xue-Bing Wu, Yuming Fu, and 4 more authors

Monthly Notices of the Royal Astronomical Society, Jul 2025

Abs DOI ADS arXiv

Slitless spectroscopy is a traditional method for selecting quasars. In this paper, we develop a procedure for selecting quasars (QSOs) using the 3D-HST G141 slitless spectra. We initially identify over 6000 sources with emission line width broader than typical emission line galaxies (ELGs) by analysing the 1D spectra. These ’broad’ emission lines may originate from QSO’s broad lines (\rm FWHM\ge 1200~\rm km s^-1) or ELG’s convolved narrow lines (\rm FWHM = 200∼300 km s^-1) with effective radii \ge0.3 arcsec (2.5 Kpc at z = 1). We then propose a criterion based on the reliability of the QSO component in the forward modeling results. Using the known QSOs, ELGs, and simulation data, we find that our criterion successfully selects about 90 per cent of known QSOs with H α or H β line detection and point-like structures, with an ELG contamination rate of about 5 per cent. We apply this method to emission line sources without significant contamination and select 19 QSO candidates at redshift z=0.12\!-\!1.56. 12 of these candidates have Chandra X-ray detections. This sample covers a broader range of the rest-frame UV colours and has redder optical slopes compared to the SDSS QSOs, yet it is likely to be composed of normal QSOs rather than little red dots. Through spectral analysis, the estimated black hole masses of the sample are 10^6.9\!-\!10^8.3 \,\rm M_⊙. Our new candidates improve the completeness of the QSO sample at z=0.8\!-\!1.6 in the 3D-HST field. The proposed method will also be helpful for QSO selections via slitless spectroscopy in Euclid and the Chinese Space Station Telescope.

@article{2025MNRAS.540.2216P, author = {{Pang}, Yuxuan and {Wu}, Xue-Bing and {Fu}, Yuming and {Zhu}, Rui and {Ji}, Tao and {Ma}, Qinchun and {Feng}, Xiaotong}, title = {{Quasar identifications from the slitless spectra: a test from 3D-HST}}, journal = {\mnras}, year = {2025}, month = jul, volume = {540}, number = {3}, pages = {2216-2237}, doi = {10.1093/mnras/staf849}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.540.2216P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, sample selection, spectroscopy, x-ray}, eprint = {2505.14025}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs

Pierluigi Rinaldi, George H. Rieke, Zihao Wu, and 23 more authors

arXiv e-prints, Jul 2025

Abs DOI ADS arXiv

Little Red Dots (LRDs) are compact, red sources discovered by JWST at high redshift (z rsim 4), marked by distinctive “V-shaped” spectral energy distributions (SEDs) and often interpreted as rapidly accreting AGNs. Their evolution remains unclear, as identifying counterparts at lower redshifts is challenging. We present WISEA J123635.56+621424.2 (here dubbed {\textbackslashit the Saguaro}), a z=2.0145 galaxy in GOODS- North, as a possible analog of high-redshift LRDs and a potential missing link in their evolutionary path toward lower- redshift systems. It features a compact LRD-like nucleus surrounded by a face-on spiral host. Its connection to LRDs includes that: (1) its nuclear spectrum shows a clear “V-shaped” SED; and (2) when redshifted to z=7, surface brightness dimming makes the host undetectable, thus mimicking an LRD. This suggests that high-redshift LRDs may be embedded in extended hosts. To test this, we stack rest-frame UV images of 99 photometrically selected LRDs, revealing faint, diffuse emission. Stacking in redshift bins reveals mild radial growth, consistent with the expected galaxy size evolution. A simple analytic model confirms that surface brightness dimming alone can explain their compact appearance. Lastly, we show that {\textbackslashit the Saguaro} is not unique by describing similar objects from the literature at z\lesssim3.5. Taken together, our results support a scenario in which LRDs may not be a distinct population, but could be the visible nuclei of galaxies undergoing a short-lived, AGN-dominated evolutionary phase, with their compact, red appearance driven largely by observational biases.

@article{2025arXiv250717738R, author = {{Rinaldi}, Pierluigi and {Rieke}, George H. and {Wu}, Zihao and {Gilbert}, Carys J. E. and {Pacucci}, Fabio and {Barchiesi}, Luigi and {Alberts}, Stacey and {Carniani}, Stefano and {Bunker}, Andrew J. and {Bhatawdekar}, Rachana and {D'Eugenio}, Francesco and {Ji}, Zhiyuan and {Johnson}, Benjamin D. and {Hainline}, Kevin and {Kokorev}, Vasily and {Kumari}, Nimisha and {Iani}, Edoardo and {Lyu}, Jianwei and {Maiolino}, Roberto and {Parlanti}, Eleonora and {Robertson}, Brant E. and {Sun}, Yang and {Vignali}, Cristian and {Williams}, Christina C. and {Willmer}, Christopher N. A. and {Zhu}, Yongda}, title = {{Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = jul, eid = {arXiv:2507.17738}, pages = {arXiv:2507.17738}, doi = {10.48550/arXiv.2507.17738}, archiveprefix = {arXiv}, eprint = {2507.17738}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250717738R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {host galaxy, jwst, local counterpart, photometry, sed}, month_numeric = {7} }

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Role of the neutral X-fermion in describing the dark matter of the universe

Remo Ruffini and Gregory Vereshchagin

European Physical Journal C, Jul 2025

Abs DOI ADS

Decades of progress culminating in the optical interferometry developed in the Keck Observatory and VLT GRAVITY facility led to the determination of the mass of the compact object in Sgr A* in 4.3 \texttimes106M\ensuremath⊙ and firm limits on its angular momentum. The most straightforward interpretation of these observations is a Schwarzschild black hole (BH). Considering that the S cluster of stars orbiting the Galactic Center does not probe distances closer than 1400 its Schwarzschild radius, several alternatives were proposed. Among them the self- gravitating system of Dark Matter (DM) fermions (here referred to as X-fermion) having a quantum degenerate core and extended to non-degenerate isothermal halo. Application of this model to our Galaxy results in a bound on X-fermion mass mX>56 keV. Upon accreting baryonic matter the degenerate fermionic core may collapse into a BH providing seeds to Active Galactic Nuclei (AGNs) and SuperMassive Black Holes (SMBHs). We address the implications of DM X-fermions with mass mX\ensuremath∼300 keV endowed with a large and negative chemical potential here evaluated on structure formation and its evolution with redshift. The Jeans mass of X-fermions peaks at 1010M\ensuremath⊙ at redshift z\ensurema th∼109, which sets the scale of galactic structures. The degenerate cores forming as early as z\ensuremath∼14 are consistent with recent observations of the James Web Space Telescope (JWST) disclosing the Little Red Dots (LRDs) at cosmological redshifts 4z12 harboring SMBHs in the range 106-109M\ensuremath⊙. Assuming that Sgr A* is not yet a BH, the lower limit on SMBH mass of 4.3\texttimes106M\ensuremath⊙ and the corresponding upper limit on the X-fermion mass of mX381 keV are established, which acquires relevance given ongoing JWST observations of the Galactic Center and the planning of new accelerators for the scrutiny of DM in CERN.

@article{2025EPJC...85..753R, author = {{Ruffini}, Remo and {Vereshchagin}, Gregory}, title = {{Role of the neutral X-fermion in describing the dark matter of the universe}}, journal = {European Physical Journal C}, keywords = {Physical Sciences, Astronomical and Space Sciences}, year = {2025}, month = jul, volume = {85}, number = {7}, eid = {753}, pages = {753}, doi = {10.1140/epjc/s10052-025-14404-6}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025EPJC...85..753R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, non-agn, theory}, month_numeric = {7} }

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JWST/MIRI Reveals the True Number Density of Massive Galaxies in the Early Universe

Tao Wang, Hanwen Sun, Luwenjia Zhou, and 14 more authors

The Astrophysical Journal Letters, Jul 2025

Abs DOI ADS arXiv

Early JWST studies reporting an unexpected abundance of massive galaxies at z \ensuremath∼ 5–8 challenge galaxy formation models in the \ensuremathΛCDM framework. Previous stellar mass (M_\ensuremath⋆) estimates suffered from large uncertainties due to the lack of rest-frame near-infrared data. Using deep JWST/NIRCam and Mid-Infrared Instrument (MIRI) photometry from Public Release IMaging for Extragalactic Research, we systematically analyze massive galaxies at z \ensuremath∼ 3–8, leveraging rest-frame \ensuremath≳1 \ensuremathμm constraints. We find MIRI is critical for robust M_\ensuremath⋆ measurements for massive galaxies at z > 5: excluding MIRI overestimates M_\ensuremath⋆ by \ensuremath∼0.4 dex on average for M_\ensuremath⋆ > 10^10M_\ensuremath⊙ galaxies, with no significant effects at lower masses. This reduces number densities of M_\ensuremath⋆ > 10^10M_\ensuremath⊙ (10^10.3M_\ensuremath⊙) galaxies by \ensuremath∼36% (55%). MIRI inclusion also reduces “Little Red Dot” (LRD) contamination in massive galaxy samples, lowering the LRD fraction from \ensuremath∼32% to \ensuremath∼13% at M_\ensuremath⋆ > 10^10.3M_\ensuremath⊙. Assuming pure stellar origins, LRDs exhibit M_\ensuremath⋆ \ensuremath∼ 10^9–10.5M_\ensuremath⊙ with MIRI constraints, rarely exceeding 10^10.5M_\ensuremath⊙. Within standard \ensuremathΛCDM, our results indicate a moderate increase in the baryon-to-star conversion efficiency (ϵ) toward higher redshifts and masses at z > 3. For the most massive z \ensuremath∼ 8 galaxies, ϵ \ensuremath∼ 0.3, compared to ϵ \ensuremath≲ 0.2 for typical galaxies at z < 3. This result is consistent with models where high gas densities and short free-fall times suppress stellar feedback in massive high-z halos.

@article{2025ApJ...988L..35W, author = {{Wang}, Tao and {Sun}, Hanwen and {Zhou}, Luwenjia and {Xu}, Ke and {Cheng}, Cheng and {Li}, Zhaozhou and {Chen}, Yangyao and {Mo}, H. J. and {Dekel}, Avishai and {Yang}, Tiancheng and {Wang}, Yijun and {Chen}, Longyue and {Zheng}, Xianzhong and {Cai}, Zheng and {Elbaz}, David and {Dai}, Y. -S. and {Huang}, J. -S.}, title = {{JWST/MIRI Reveals the True Number Density of Massive Galaxies in the Early Universe}}, journal = {\apjl}, keywords = {Galaxy formation, Early universe, High-redshift galaxies, Cosmology, 595, 435, 734, 343}, year = {2025}, month = jul, volume = {988}, number = {1}, eid = {L35}, pages = {L35}, doi = {10.3847/2041-8213/adebe7}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...988L..35W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, photometry, sed}, altmetric = {160374849}, eprint = {2403.02399}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {7} }

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Little Red Dots from Small-Scale Primordial Black Hole Clustering

Borui Zhang, Wei-Xiang Feng, and Haipeng An

arXiv e-prints, Jul 2025

Abs ADS arXiv

The James Webb Space Telescope (JWST) observations have identified a class of compact galaxies at high redshifts (4 ≲z ≲11), dubbed “little red dots” (LRDs). The supermassive black holes (SMBHs) of 10^5-8\rm M_⊙ in LRDs favor a heavy-seed origin. We propose a mechanism for their formation: Clusters of primordial black holes, formed through long-short mode coupling on small scales in the early Universe, undergo sequential mergers over extended timescales. This mechanism can evade cosmic microwave background distortions and result in heavy-seed SMBHs via runaway mergers. We employ Monte Carlo simulations to solve the Smoluchowski coagulation equation and determine the runaway merging timescale. The resulting stochastic gravitational wave background offers a distinct signature of this process, and the forming SMBHs can be highly spinning at their formation due to the spin residual of the cluster from tidal fields. This mechanism may explain the rapidly spinning SMBHs in LRDs under the assumption of obscured active galactic nuclei.

@article{2025arXiv250707171Z, author = {{Zhang}, Borui and {Feng}, Wei-Xiang and {An}, Haipeng}, title = {{Little Red Dots from Small-Scale Primordial Black Hole Clustering}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology}, year = {2025}, month = jul, eid = {arXiv:2507.07171}, pages = {arXiv:2507.07171}, archiveprefix = {arXiv}, eprint = {2507.07171}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250707171Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, month_numeric = {7} }

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Here There Be (Dusty) Monsters: High-redshift Active Galactic Nuclei Are Dustier than Their Hosts

Madisyn Brooks, Raymond C. Simons, Jonathan R. Trump, and 15 more authors

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

JWST spectroscopy has discovered a population of z \ensuremath≳ 3.5 galaxies with broad Balmer emission lines and narrow forbidden lines that are consistent with hosting active galactic nuclei (AGN). Many of these systems, now known as “little red dots,” are compact and have unique colors that are very red in the optical/near-infrared and blue in the ultraviolet. The relative contribution of galaxy starlight and AGN to these systems remains uncertain, especially for the galaxies with unusual blue+red spectral energy distributions. In this work, we use Balmer decrements to measure the independent dust attenuation of the broad and narrow emission-line components of a sample of 29 broad-line AGN identified from three public JWST spectroscopy surveys: CEERS, JADES, and RUBIES. Stacking the narrow components from the spectra of 25 sources with broad H\ensuremathα and no broad H\ensuremathβ results in a median narrow H\ensuremathα/H\ensuremathβ = 2.47‑0.05+0.05 (consistent with A_v = 0) and broad H\ensuremathα/H\ensuremathβ >8.85 (A_v > 3.63). The narrow and broad Balmer decrements imply little to no attenuation of the narrow emission lines, which are consistent with being powered by star formation and located on larger physical scales. Meanwhile, the lower limit in the broad H\ensuremathα/H\ensuremathβ decrement, with broad H\ensuremathβ undetected in the stacked spectrum of 25 broad H\ensuremathα AGN, implies significant dust attenuation of the broad-line emitting region that is presumably associated with the central AGN. Our results indicate that these systems, on average, are consistent with heavily dust-attenuated AGN powering the red parts of their SED, while their blue UV emission is powered by unattenuated star formation in the host galaxy.

@article{2025ApJ...986..177B, author = {{Brooks}, Madisyn and {Simons}, Raymond C. and {Trump}, Jonathan R. and {Taylor}, Anthony J. and {Bagley}, Micaela B. and {Backhaus}, Bren and {Davis}, Kelcey and {Buat}, V{\'e}ronique and {Cleri}, Nikko J. and {de la Vega}, Alexander and {Finkelstein}, Steven L. and {Hirschmann}, Michaela and {Holwerda}, Benne W. and {Kocevski}, Dale D. and {Koekemoer}, Anton M. and {Lucas}, Ray A. and {Pacucci}, Fabio and {Seill{\'e}}, Lise-Marie}, title = {{Here There Be (Dusty) Monsters: High-redshift Active Galactic Nuclei Are Dustier than Their Hosts}}, journal = {\apj}, keywords = {Active galactic nuclei, AGN host galaxies, High-redshift galaxies, Supermassive black holes, Spectroscopy, 16, 2017, 734, 1663, 1558}, year = {2025}, month = jun, volume = {986}, number = {2}, eid = {177}, pages = {177}, doi = {10.3847/1538-4357/addac4}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986..177B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, sed, spectroscopy}, eprint = {2410.07340}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Exploring the Active Galactic Nucleus Fraction of a Sample of JWST’s Little Red Dots at 4 < z < 8: Overmassive Black Holes Are Strongly Favored

Emmanuel Durodola, Fabio Pacucci, and Ryan C. Hickox

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

JWST is revolutionizing our view of the early Universe by pushing the boundaries of detectable galaxies and black holes in redshift (upward) and mass (downward). The little red dots (LRDs), detected by several surveys at z > 4, present a significant interpretational challenge, as their spectral energy distributions (SEDs) can mimic both active galactic nucleus (AGN) and stellar population templates. This study analyzes 19 LRDs from the JWST Advanced Deep Extragalactic Survey survey, utilizing NIRCam and MIRI photometry. By performing SED fitting across a vast parameter space, we explore a broad range of AGN fractions, defined as the ratio of the monochromatic luminosities (AGN, galaxy, and dust) over a specified wavelength range, 0.4–0.7 \ensuremathμm rest frame. We find that 17 of the 19 LRDs investigated are consistent with having significant AGN contributions, with best-fitting AGN fractions ranging between 20% and 70%, while one galaxy shows a low AGN contribution (2%) and another appears to be purely star forming. Moreover, assuming these LRDs do indeed host AGN, we can place limits on their black hole masses using the inferred AGN bolometric luminosities and adopting the Eddington limit. We find that, independent of the specific AGN fraction adopted, the LRDs’ black holes are significantly overmassive relative to their host galaxies—by \ensuremath∼1 dex, and up to \ensuremath∼4 dex in the most extreme cases—compared to the local M_•–M_\ensuremath⋆ relation. The presence of overmassive black holes in the high-z Universe may provide the strongest evidence yet of heavy black hole seeding occurring during the cosmic dark ages.

@article{2025ApJ...985..169D, author = {{Durodola}, Emmanuel and {Pacucci}, Fabio and {Hickox}, Ryan C.}, title = {{Exploring the Active Galactic Nucleus Fraction of a Sample of JWST's Little Red Dots at 4 < z < 8: Overmassive Black Holes Are Strongly Favored}}, journal = {\apj}, keywords = {Active galaxies, Supermassive black holes, Galaxy evolution, High-redshift galaxies, Scaling relations, 17, 1663, 594, 734, 2031}, year = {2025}, month = jun, volume = {985}, number = {2}, eid = {169}, pages = {169}, doi = {10.3847/1538-4357/adced2}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...985..169D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {164629402}, lrdkeys = {black hole mass, early universe, jwst, photometry, sed}, eprint = {2406.10329}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Dark Bondi Accretion Aided by Baryons and the Origin of JWST Little Red Dots

Wei-Xiang Feng, Hai-Bo Yu, and Yi-Ming Zhong

arXiv e-prints, Jun 2025

Abs ADS arXiv

The gravothermal core collapse of self-interacting dark matter halos provides a compelling mechanism for seeding supermassive black holes in the early Universe. In this scenario, a small fraction of a halo, approximately 1% of its mass, collapses into a dense core, which could further evolve into a black hole. We demonstrate that this process can account for the origin of JWST little red dots (LRDs) observed at redshifts z\sim4-11, where black holes with masses of 10^7\rm M_⊙ can form within 500\rm Myr after the formation of host halos with masses of 10^9\rm M_⊙. Even if the initial collapse region triggering general-relativistic instability has a mass on the order of one solar mass, the resulting seed can grow into an intermediate-mass black hole via Eddington accretion of baryonic gas. Subsequently, it can continue to grow into a supermassive black hole through dark Bondi accretion of dark matter particles. In this scenario, the majority of the black hole’s mass originates from dark matter accretion rather than baryonic matter, naturally explaining the overmassive feature of LRDs.

@article{2025arXiv250617641F, author = {{Feng}, Wei-Xiang and {Yu}, Hai-Bo and {Zhong}, Yi-Ming}, title = {{Dark Bondi Accretion Aided by Baryons and the Origin of JWST Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology}, year = {2025}, month = jun, eid = {arXiv:2506.17641}, pages = {arXiv:2506.17641}, archiveprefix = {arXiv}, eprint = {2506.17641}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250617641F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, theory}, month_numeric = {6} }

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Investigating photometric and spectroscopic variability in the multiply imaged little red dot A2744-QSO1

Lukas J. Furtak, Amy R. Secunda, Jenny E. Greene, and 25 more authors

Astronomy & Astrophysics, Jun 2025

Abs DOI ADS arXiv

JWST observations have uncovered a new population of red, compact objects at high redshifts dubbed “little red dots” (LRDs), which typically show broad emission lines and are thought to be dusty active galactic nuclei (AGNs). Some of their other features, however, challenge the AGN explanation, such as prominent Balmer breaks and extremely faint or even missing metal high-ionization lines, X-ray, or radio emission, including in deep stacks. Time variability is another robust test of AGN activity. Here, we exploit the z = 7.045 multiply imaged LRD A2744-QSO1, which offers a particularly unique test of variability due to lensing-induced time delays between the three images spanning 22 yr (2.7 yr in the rest-frame), to investigate its photometric and spectroscopic variability. We find the equivalent widths (EWs) of the broad H\ensuremathα and H\ensuremathβ lines, which are independent of magnification and other systematics, to exhibit significant variations, of up to 18 \ensuremath\pm 3% for H\ensuremathα and up to 22 \ensuremath\pm 8% in H\ensuremathβ, on a timescale of 875 d (2.4 yr) in the rest-frame. This suggests that A2744-QSO1 is indeed an AGN. We find no significant photometric variability beyond the limiting systematic uncertainties, so it currently cannot be determined whether the EW variations are due to line-flux or continuum variability. These results are consistent with a typical damped random walk variability model for an AGN such as A2744-QSO1 (M_BH = 4 \texttimes 10^7 M_\ensuremath⊙) given the sparse sampling of the light curve with the available data. Our results therefore support the AGN interpretation of this LRD, and highlight the need for further photometric and spectroscopic monitoring in order to build a detailed and reliable light curve.

@article{2025A&A...698A.227F, author = {{Furtak}, Lukas J. and {Secunda}, Amy R. and {Greene}, Jenny E. and {Zitrin}, Adi and {Labb{\'e}}, Ivo and {Golubchik}, Miriam and {Bezanson}, Rachel and {Kokorev}, Vasily and {Atek}, Hakim and {Brammer}, Gabriel B. and {Chemerynska}, Iryna and {Cutler}, Sam E. and {Dayal}, Pratika and {Feldmann}, Robert and {Fujimoto}, Seiji and {Glazebrook}, Karl and {Leja}, Joel and {Ma}, Yilun and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Nelson}, Erica J. and {Oesch}, Pascal A. and {Pan}, Richard and {Price}, Sedona H. and {Suess}, Katherine A. and {Wang}, Bingjie and {Weaver}, John R. and {Whitaker}, Katherine E.}, title = {{Investigating photometric and spectroscopic variability in the multiply imaged little red dot A2744-QSO1}}, journal = {\aap}, keywords = {gravitational lensing: strong, galaxies: high-redshift, quasars: emission lines, quasars: supermassive black holes, quasars: individual: A2744-QSO1}, year = {2025}, month = jun, volume = {698}, eid = {A227}, pages = {A227}, doi = {10.1051/0004-6361/202554110}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...698A.227F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, spectroscopy, variability}, altmetric = {174139057}, eprint = {2502.07875}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Another Piece to the Puzzle: Radio Detection of a JWST-detected Active Galactic Nucleus Candidate

Anniek J. Gloudemans, Kenneth J. Duncan, Anna-Christina Eilers, and 5 more authors

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

Radio observations can provide crucial insight into the nature of a new abundant and mysterious population of dust-reddened active galactic nuclei (AGN) candidates discovered by the James Webb Space Telescope (JWST), including “Little Red Dots.” In this study, we search for radio bright sources in a large sample of \ensuremath∼700 JWST-discovered AGN candidates (z \ensuremath∼ 2–11) in the 0.144–3 GHz frequency range, utilizing deep radio imaging in the Cosmic Evolution Survey and Great Observatories Origins Deep Survey North and South. Only one source, PRIMER-COS 3866 at z = 4.66, is significantly detected in our radio surveys, which has been previously identified as an X-ray AGN. Its radio properties are consistent with both an AGN and star formation origin with a spectral index of \ensuremat hα=‑0 .76‑0.09+0.11 , radio-loudness of R \ensuremath≈ 0.5, and brightness temperature limit of T_b \ensuremath≳ 10^3 K. Our stacking results of both spectroscopically and photometrically selected AGN candidates yield nondetections in all fields, with 3\ensuremathσ limits of L_1.4 GHz < 8.6 \texttimes 10^39 erg s^‑1 (spectroscopic sample) and L_1.3 GHz < 1.3 \texttimes 10^39 erg s^‑1 (photometric sample). We demonstrate that these results are still consistent with expectations from the empirical L_X–L_H\ensuremathα and L_X–L_R correlations established for local AGN. We argue that current radio observations in these studied fields have insufficient depth to claim JWST-discovered AGN candidates are radio weak. We project that future surveys carried out by the Square Kilometer Array and Next Generation Very Large Array should be able to obtain significant detections within a few hours, providing crucial measurements of their brightness temperature, which would allow for distinguishing between AGN and starburst-driven origins of this new abundant population.

@article{2025ApJ...986..130G, author = {{Gloudemans}, Anniek J. and {Duncan}, Kenneth J. and {Eilers}, Anna-Christina and {Farina}, Emanuele Paolo and {Harikane}, Yuichi and {Inayoshi}, Kohei and {Lambrides}, Erini and {Vardoulaki}, Eleni}, title = {{Another Piece to the Puzzle: Radio Detection of a JWST-detected Active Galactic Nucleus Candidate}}, journal = {\apj}, keywords = {High-redshift galaxies, Radio continuum emission, Active galactic nuclei, James Webb Space Telescope, 734, 1340, 16, 2291}, year = {2025}, month = jun, volume = {986}, number = {2}, eid = {130}, pages = {130}, doi = {10.3847/1538-4357/adddb9}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986..130G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, multi-wavelength, radio, x-ray}, altmetric = {172893653}, eprint = {2501.04912}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Where Have All the Little Red Dots Gone? Supermassive Black Hole Binary Dynamics and Its Impact on Galaxy Properties

Fazeel Mahmood Khan, Benjamin L. Davis, Andrea Valerio Macciò, and 1 more author

The Astrophysical Journal Letters, Jun 2025

Abs DOI ADS arXiv

Recent James Webb Space Telescope observations have revealed a peculiar class of galaxies at redshifts z \ensuremath≳ 6, characterized by extremely high central stellar densities and overmassive central supermassive black holes (SMBHs), “little red dots” (LRDs). A critical question remains: if LRDs were common at high redshifts, how would they evolve into local elliptical galaxies with significantly lower central densities? To address this, we performed direct N-body simulations of LRD mergers, focusing on the coevolution of host galaxies and central SMBHs. We track the complete evolution of SMBH binaries into the three-body hardening and gravitational-wave (GW) emission phase. Our results demonstrate that during galaxy mergers, the central SMBHs can eject a substantial amount of mass from the galactic core via the three-body slingshot effect, leading to a decrease in central stellar surface density by an order of magnitude. Additionally, GW recoil can further contribute in making the galaxy centers less dense and more in alignment with low-redshift quiescent galaxies. This transformation occurs on a relatively short timescale of a few \ensuremath∼100 Myr, implying that LRDs can evolve into lower-redshift elliptical galaxies by z < 4. The timescales for our SMBH mergers vary between 100 and 800 Myr, depending on the initial orbital parameters of the merging galaxies and the mass ratio of the SMBHs. Our findings provide a plausible mechanism for the transformation of LRDs into elliptical galaxies while highlighting the efficiency of SMBH mergers in such high-density environments, which plays a crucial role in SMBH growth.

@article{2025ApJ...986L...1K, author = {{Khan}, Fazeel Mahmood and {Davis}, Benjamin L. and {Macci{\`o}}, Andrea Valerio and {Holley-Bockelmann}, Kelly}, title = {{Where Have All the Little Red Dots Gone? Supermassive Black Hole Binary Dynamics and Its Impact on Galaxy Properties}}, journal = {\apjl}, keywords = {Black hole physics, 159}, year = {2025}, month = jun, volume = {986}, number = {1}, eid = {L1}, pages = {L1}, doi = {10.3847/2041-8213/adda4c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986L...1K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, host galaxy, jwst, simulation, theory}, altmetric = {175093686}, eprint = {2503.07711}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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The Rise of Faint, Red Active Galactic Nuclei at z > 4: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields

Dale D. Kocevski, Steven L. Finkelstein, Guillermo Barro, and 54 more authors

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

We present a sample of 341 “little red dots” (LRDs) spanning the redshift range z \ensuremath∼ 2–11 using data from the CEERS, PRIMER, JADES, UNCOVER, and NGDEEP surveys. Unlike past use of color indices to identify LRDs, we employ continuum slope fitting using shifting bandpasses to sample the same rest-frame emission blueward and redward of the Balmer break. This enables the detection of LRDs over a wider redshift range and with less contamination from galaxies with strong breaks that otherwise lack a rising red continuum. The redshift distribution of our sample increases at z log(NH/cm2 ) of 23. 3‑1.3+0.4 and 22. 72‑0.16+0.13 . Our analysis reveals that reddened AGN emission dominates their rest-optical light, while the rest-UV originates from their host galaxies. We also present NIRSpec observations from the RUBIES survey of 17 LRDs that show broad emission lines consistent with AGN activity. The confirmed AGN fraction of our sample is 71% for sources with F444W < 26.5. In addition, we find three LRDs with blueshifted Balmer absorption features in their spectra, suggesting an outflow of high-density, low-ionization gas from near the central engine of these faint, red AGN.

@article{2025ApJ...986..126K, author = {{Kocevski}, Dale D. and {Finkelstein}, Steven L. and {Barro}, Guillermo and {Taylor}, Anthony J. and {Calabr{\`o}}, Antonello and {Laloux}, Brivael and {Buchner}, Johannes and {Trump}, Jonathan R. and {Leung}, Gene C. K. and {Yang}, Guang and {Dickinson}, Mark and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Pacucci}, Fabio and {Inayoshi}, Kohei and {Somerville}, Rachel S. and {McGrath}, Elizabeth J. and {Akins}, Hollis B. and {Bagley}, Micaela B. and {Bowler}, Rebecca A. A. and {Bisigello}, Laura and {Carnall}, Adam and {Casey}, Caitlin M. and {Cheng}, Yingjie and {Cleri}, Nikko J. and {Costantin}, Luca and {Cullen}, Fergus and {Davis}, Kelcey and {Donnan}, Callum T. and {Dunlop}, James S. and {Ellis}, Richard S. and {Ferguson}, Henry C. and {Fujimoto}, Seiji and {Fontana}, Adriano and {Giavalisco}, Mauro and {Grazian}, Andrea and {Grogin}, Norman A. and {Hathi}, Nimish P. and {Hirschmann}, Michaela and {Huertas-Company}, Marc and {Holwerda}, Benne W. and {Illingworth}, Garth and {Juneau}, St{\'e}phanie and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Li}, Wenxiu and {Lucas}, Ray A. and {Magee}, Dan and {Mason}, Charlotte and {McLeod}, Derek J. and {McLure}, Ross J. and {Napolitano}, Lorenzo and {Papovich}, Casey and {Pirzkal}, Nor and {Rodighiero}, Giulia and {Santini}, Paola and {Wilkins}, Stephen M. and {Yung}, L. Y. Aaron}, title = {{The Rise of Faint, Red Active Galactic Nuclei at z > 4: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields}}, journal = {\apj}, keywords = {Active galactic nuclei, Supermassive black holes, 16, 1663}, year = {2025}, month = jun, volume = {986}, number = {2}, eid = {126}, pages = {126}, doi = {10.3847/1538-4357/adbc7d}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986..126K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, spectroscopy, x-ray}, altmetric = {178125502}, eprint = {2404.03576}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Black Holes in the Red-sequence Elliptical Galaxies at Redshifts ∼0.7-2.5: Not Dark Energy Source but Remanants of Little Red Dots

Lei Lei, Ze-Fan Wang, Yi-Ying Wang, and 2 more authors

arXiv e-prints, Jun 2025

Abs ADS arXiv

The nature of dark energy remains one of the most profound mysteries in modern cosmology. One intriguing proposal is that black holes (BHs) could be the astrophysical source of dark energy through a cosmological coupling mechanism, and strong evidence has been claimed via analyzing the growth of the black hole masses in the red-sequence elliptical galaxies at redshifts ≤2.5. In this work, with a group of very high redshift AGNs detected by the James Webb Space Telescope (JWST) in the red-sequence elliptical galaxies, we show that the possibility of BHs being the astrophysical source of dark energy has been rejected at a confidence level exceeding 10σ. Moreover, it turns out that the Little Red Dots recently discovered by JWST, characterized by the low accretion rates, can naturally evolve into the red- sequence elliptical galaxies hosting the relatively low mass black holes at the redshifts of ∼0.7-2.5, without the need of black hole cosmological coupling.

@article{2025arXiv250619589L, author = {{Lei}, Lei and {Wang}, Ze-Fan and {Wang}, Yi-Ying and {Feng}, Lei and {Fan}, Yi-Zhong}, title = {{Black Holes in the Red-sequence Elliptical Galaxies at Redshifts $\sim 0.7-2.5$: Not Dark Energy Source but Remanants of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology}, year = {2025}, month = jun, eid = {arXiv:2506.19589}, pages = {arXiv:2506.19589}, archiveprefix = {arXiv}, eprint = {2506.19589}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250619589L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, non-agn}, month_numeric = {6} }

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Possible environmental quenching in an interacting little red dot pair at z \ensuremath∼ 7

Rosa M. Mérida, Gaia Gaspar, Marcin Sawicki, and 14 more authors

Astronomy & Astrophysics, Jun 2025

Abs DOI ADS arXiv

We report the discovery of a z \ensuremath∼ 7 group of galaxies that contains two little red dots (LRDs) just 3.3 kpc apart, along with three potential satellite galaxies, as part of the Canadian NIRISS Unbiased Cluster Survey (CANUCS). The spectral energy distributions (SEDs) of this LRD pair show evidence of a Balmer break, consistent with a recent (\ensuremath∼100 Myr) quenching of star formation. In contrast, the satellites are compatible with a recent-onset (\ensuremath∼100 Myr), ongoing burst of star formation. LRD1’s SED is consistent with a dust-free active galactic nucleus (AGN) being the source of the UV excess in the galaxy. The optical continuum would be powered by the emission from an obscured post-starburst and the AGN at a subdominant level. LRD2’s SED is more ambiguous, but it could also be indicative of a dust-free AGN. In this scenario, these LRDs would be massive (M_\ensuremath⋆ \ensuremath∼ 10^10 M_\ensuremath⊙) and dusty (A(V) > 1 mag) and the three satellites would be lower- mass objects (M_\ensuremath⋆ \ensuremath∼ 10^8 ‑ 9 M_\ensuremath⊙) subject to low dust attenuations. The proximity of the two LRDs suggests that their interaction is responsible for their recent star formation histories, which can be interpreted as environmental bursting and quenching in the epoch of reionization.

@article{2025A&A...698A.317M, author = {{M{\'e}rida}, Rosa M. and {Gaspar}, Gaia and {Sawicki}, Marcin and {Asada}, Yoshihisa and {Desprez}, Guillaume and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Antwi-Danso}, Jacqueline and {Tripodi}, Roberta and {Willott}, Chris J. and {Brada{\v{c}}}, Maru{\v{s}}a and {Brammer}, Gabriel B. and {Iyer}, Kartheik G. and {Martis}, Nicholas S. and {Muzzin}, Adam and {Noirot}, Ga{\"e}l and {Sarrouh}, Ghassan T. E. and {Markov}, Vladan}, title = {{Possible environmental quenching in an interacting little red dot pair at z {\ensuremath{\sim}} 7}}, journal = {\aap}, keywords = {galaxies: active, galaxies: evolution, galaxies: high-redshift, galaxies: interactions}, year = {2025}, month = jun, volume = {698}, eid = {A317}, pages = {A317}, doi = {10.1051/0004-6361/202553943}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...698A.317M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {173648133}, lrdkeys = {clustering, dust, early universe, sed, starburst}, eprint = {2501.17925}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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A little red dot up close

Lindsay Oldham

Nature Astronomy, Jun 2025

DOI ADS

@article{2025NatAs...9..776O, author = {{Oldham}, Lindsay}, title = {{A little red dot up close}}, journal = {Nature Astronomy}, year = {2025}, month = jun, volume = {9}, pages = {776-776}, doi = {10.1038/s41550-025-02599-3}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NatAs...9..776O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {178218301}, lrdkeys = {case study, dust, non-agn, sed, starburst}, month_numeric = {6} }

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The VLA Frontier Fields Survey: A 6GHz High-resolution Radio Survey of Abell 2744

Esteban A. Orozco, Eric F. Jiménez-Andrade, Eric J. Murphy, and 5 more authors

arXiv e-prints, Jun 2025

Abs ADS arXiv

We present a 6GHz radio continuum image of the galaxy cluster Abell 2744 (z = 0.307) obtained with the Karl G. Jansky Very Large Array (VLA) as part of the VLA Frontier Fields program, whose goal is to explore the radio continuum emission from high-redshift galaxies that are magnified by foreground, massive galaxy clusters. With an rms noise of ≈1 μJy beam^-1, at the phase center, and sub-arcsec angular resolution (θ_1/2=0.82 arcsec), this is the deepest and most detailed radio image of Abell 2744 ever obtained. A total of 93 sources are detected with a peak signal-to-noise ratio \geq5, of which 46 have optical/near-infrared (IR) counterparts with available redshift, magnification (μ), and stellar mass (M_*) estimates. The radio sources are distributed over a redshift from 0.15 to 3.55, with a median redshift value of z = 0.93, and a median stellar mass of M_*= 2.3 \times 10^10\,\rmM_⊙. A comparison between the radio-based star formation rates (SFRs) and those derived from ultraviolet- to-near IR data reveals that the radio SFRs are, on average, an order of magnitude higher than the ultraviolet-to-near IR SFRs. We look for radio counterparts of the so-called “Little Red Dots (LRDs)” galaxies at z\approx6 in Abell 2744, but find no significant detections. After stacking, we derive a 3σ upper limit to the 6GHz radio luminosity of LRDs of 4.1\times 10^39\,\rm erg s^-1. Finally, we present a sample of 22 moderately/strongly lensed galaxies (μrsim 2) in the VLA Frontier Fields survey, which is adequate to zoom into star formation processes of main sequence galaxies at z≈1-2.

@article{2025arXiv250620634O, author = {{Orozco}, Esteban A. and {Jim{\'e}nez-Andrade}, Eric F. and {Murphy}, Eric J. and {Smail}, Ian and {Momjian}, Emmanuel and {Heywood}, Ian and {Vega-Gutierrez}, Miguel and {DeCoursey}, Christa}, title = {{The VLA Frontier Fields Survey: A 6GHz High-resolution Radio Survey of Abell 2744}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jun, eid = {arXiv:2506.20634}, pages = {arXiv:2506.20634}, archiveprefix = {arXiv}, eprint = {2506.20634}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250620634O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {multi-wavelength, non-jwst, photometry, radio, starburst}, month_numeric = {6} }

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’Little red dots’ cannot reside in the same dark matter haloes as comparably luminous unobscured quasars

Elia Pizzati, Joseph F. Hennawi, Joop Schaye, and 4 more authors

Monthly Notices of the Royal Astronomical Society, Jun 2025

Abs DOI ADS arXiv

The JWST has uncovered a new population of candidate broad-line active galactic nucleus (AGN) emerging in the early Universe, named ’little red dots’ (LRDs) because of their compactness and red colours at optical wavelengths. LRDs appear to be surprisingly abundant (≈ 10^-5  \rm cMpc^-3) given that their inferred bolometric luminosities largely overlap with those of the ultraviolet (UV)-luminous quasars identified at high z in wide-field spectroscopic surveys. In this work, we investigate how the population of LRDs and/or other UV-obscured AGN relates to the one of unobscured, UV-selected quasars. By comparing their number densities, we infer an extremely large and rapidly evolving obscured:unobscured ratio, ranging from ≈ 20:1 at z≈4 to ≈ 2300:1 at z≈7, and possibly extending out to very high (≈ 10^47 \rm erg \rm s^-1) bolometric luminosities. This large obscured:unobscured ratio is incompatible with the UV-luminous duty cycle measured for unobscured quasars at z≈4\!-\!6, suggesting that LRDs are too abundant to be hosted by the same haloes as unobscured quasars. This implies that either (a) the bolometric luminosities of LRDs are strongly overestimated or (b) LRDs follow different scaling relations than those of UV-selected quasars, representing a new population of accreting supermassive black holes emerging in the early Universe. A direct comparison between the clustering of LRDs and that of faint UV-selected quasars will ultimately confirm these findings and shed light on key properties of LRDs such as their host mass distribution and duty cycle. We provide a mock analysis for the clustering of LRDs and show that it is feasible with current and upcoming JWST surveys.

@article{2025MNRAS.539.2910P, author = {{Pizzati}, Elia and {Hennawi}, Joseph F. and {Schaye}, Joop and {Eilers}, Anna-Christina and {Huang}, Jiamu and {Schindler}, Jan-Torge and {Wang}, Feige}, title = {{'Little red dots' cannot reside in the same dark matter haloes as comparably luminous unobscured quasars}}, journal = {\mnras}, keywords = {galaxies: high-redshift, quasars: general, quasars: supermassive black holes, large-scale structure of Universe}, year = {2025}, month = jun, volume = {539}, number = {4}, pages = {2910-2925}, doi = {10.1093/mnras/staf660}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.539.2910P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {168768628}, lrdkeys = {black hole mass, clustering, dust, early universe, jwst}, eprint = {2409.18208}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Broad-line AGNs at 3.5 < z < 6: The Black Hole Mass Function and a Connection with Little Red Dots

Anthony J. Taylor, Steven L. Finkelstein, Dale D. Kocevski, and 48 more authors

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

We present a sample of 62 H\ensuremathα detected broad-line active galactic nuclei (BLAGNs) at redshifts 3.5 0), independent of contributions from emission lines to the broadband photometry. We construct the black hole (BH) mass function at 3.5 < z < 6 after computing robust completeness corrections. This BH mass function shows agreement with recent JWST-based BH mass functions, though we extend these earlier results to log (M_BH/M_\ensuremath⊙) < 7. The derived BH mass function is consistent with theoretical models, indicating that the observed abundance of BHs in the early Universe may not be discrepant with physically motivated predictions. The BH mass function shape resembles a largely featureless power law, suggesting that signatures from BH seeding have been lost by redshift z \ensuremath∼ 5–6. Finally, we compute the BLAGN UV luminosity function and find agreement with JWST-detected BLAGN samples from recent works, finding that BLAGN hosts constitute \ensuremath≲10% of the total observed UV luminosity at all but the brightest luminosities.

@article{2025ApJ...986..165T, author = {{Taylor}, Anthony J. and {Finkelstein}, Steven L. and {Kocevski}, Dale D. and {Jeon}, Junehyoung and {Bromm}, Volker and {Amor{\'\i}n}, Ricardo O. and {Arrabal Haro}, Pablo and {Backhaus}, Bren E. and {Bagley}, Micaela B. and {Banados}, Eduardo and {Bhatawdekar}, Rachana and {Brooks}, Madisyn and {Calabr{\`o}}, Antonello and {Ortiz}, {\'O}scar A. Ch{\'a}vez and {Cheng}, Yingjie and {Cleri}, Nikko J. and {Cole}, Justin W. and {Davis}, Kelcey and {Dickinson}, Mark and {Donnan}, Callum and {Dunlop}, James S. and {Ellis}, Richard S. and {Fern{\'a}ndez}, Vital and {Fontana}, Adriano and {Fujimoto}, Seiji and {Giavalisco}, Mauro and {Grazian}, Andrea and {Guo}, Jingsong and {Hathi}, Nimish P. and {Holwerda}, Benne W. and {Hirschmann}, Michaela and {Inayoshi}, Kohei and {Kartaltepe}, Jeyhan S. and {Khusanova}, Yana and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Larson}, Rebecca L. and {Leung}, Gene C. K. and {Lucas}, Ray A. and {McLeod}, Derek J. and {Napolitano}, Lorenzo and {Onoue}, Masafusa and {Pacucci}, Fabio and {Papovich}, Casey and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Pirzkal}, Nor and {Somerville}, Rachel S. and {Trump}, Jonathan R. and {Wilkins}, Stephen M. and {Yung}, L. Y. Aaron and {Zhang}, Haowen}, title = {{Broad-line AGNs at 3.5 < z < 6: The Black Hole Mass Function and a Connection with Little Red Dots}}, journal = {\apj}, keywords = {Supermassive black holes, Quasars, Active galactic nuclei, Broad band photometry, High-redshift galaxy clusters, High-redshift galaxies, Astrophysical black holes, Black holes, 1663, 1319, 16, 184, 2007, 734, 98, 162}, year = {2025}, month = jun, volume = {986}, number = {2}, eid = {165}, pages = {165}, doi = {10.3847/1538-4357/add15b}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986..165T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, eprint = {2409.06772}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Little Red Dots Are Tidal Disruption Events in Runaway-collapsing Clusters

Jillian Bellovary

The Astrophysical Journal Letters, May 2025

Abs DOI ADS arXiv

I hypothesize a physical explanation for the “little red dots” (LRDs) discovered by the James Webb Space Telescope (JWST). The first star formation in the Universe occurs in dense clusters, some of which may undergo runaway collapse and form an intermediate mass black hole. This process would appear as a very dense stellar system, with recurring tidal disruption events (TDEs) as stellar material is accreted by the black hole. Such a system would be compact, UV-emitting, and exhibit broad H\ensuremathα emission. If runaway collapse is the primary mechanism for forming massive black hole seeds, this process could be fairly common and explain the large volume densities of LRDs. In order to match the predicted number density of runaway collapse clusters, the tidal disruption rate must be on the order of 10^‑4 per year. A top-heavy stellar initial mass function may be required to match observations without exceeding the predicted \ensuremathΛCDM mass function. The TDE LRD hypothesis can be verified with follow-up JWST observations looking for TDE-like variability.

@article{2025ApJ...984L..55B, author = {{Bellovary}, Jillian}, title = {{Little Red Dots Are Tidal Disruption Events in Runaway-collapsing Clusters}}, journal = {\apjl}, keywords = {High-redshift galaxies, Intermediate-mass black holes, Galaxy formation, Tidal disruption, Active galactic nuclei, 734, 816, 595, 1696, 16, Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = may, volume = {984}, number = {2}, eid = {L55}, pages = {L55}, doi = {10.3847/2041-8213/adce6c}, archiveprefix = {arXiv}, eprint = {2501.03309}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...984L..55B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, heavy seed, jwst, theory}, month_numeric = {5} }

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Dot to dot: High-z little red dots in M_\textbackslashmathrm{ bh} – M_\textbackslashmathrm{ \textbackslashstar} diagrams with galaxy-morphology-specific scaling relations

Alister W. Graham, Igor Chilingarian, Dieu Duc Nguyen, and 3 more authors

\pasa, May 2025

Abs DOI ADS arXiv

The high redshift ’little red dots’ (LRDs) detected with the James Webb Space Telescope are considered to be the cores of emerging galaxies that host active galactic nuclei (AGN). For the first time, we compare LRDs with local compact stellar systems and an array of galaxy-morphology-dependent stellar mass-black hole mass scaling relations in the M_\mathrm bh – M_⋆ diagrams. When considering the 2023–2024 masses for LRDs, they are not equivalent to nuclear star clusters (NSCs), with the latter having higher M_\mathrm bh/M_⋆ ratios. However, the least massive LRDs exhibit similar M_\mathrm bh and M_\mathrm ⋆,gal values as ultracompact dwarf (UCD) galaxies, believed to be the cores of stripped/threshed galaxies. We show that the LRDs span the M_\mathrm bh – M_\mathrm ⋆,gal diagram from UCD galaxies to primaeval lenticular galaxies. In contrast, local spiral galaxies and the subset of major-merger-built early-type galaxies define M_\mathrm bh – M_⋆,gal relations that are offset to higher stellar masses. Based on the emerging 2025 masses for LRDs, they may yet have similarities with NSCs, UCD galaxies, and green peas. Irrespective of this developing situation, we additionally observe that low-redshift galaxies with AGN align with the quasi-quadratic or steeper black hole scaling relations defined by local disc galaxies with directly measured black hole masses. This highlights the benefits of considering a galaxy’s morphology – which reflects its accretion and merger history – to understand the coevolution of galaxies and their black holes. Future studies of spatially resolved galaxies with secure masses at intermediate-to-high redshift hold the promise of detecting the emergence and evolution of the galaxy-morphology-dependent M_\mathrm bh – M_⋆ relations.

@article{2025PASA...42...68G, author = {{Graham}, Alister W. and {Chilingarian}, Igor and {Nguyen}, Dieu Duc and {Soria}, Roberto and {Durr{\'e}}, Mark and {Forbes}, Duncan A.}, title = {{Dot to dot: High-z little red dots in M\_\textbackslashmathrm\{ bh\} {\textendash} M\_\textbackslashmathrm\{ \textbackslashstar\} diagrams with galaxy-morphology-specific scaling relations}}, journal = {\pasa}, keywords = {Galaxies: bulges, galaxies: elliptical and lenticular, cD, galaxies: structure, galaxies: interactions, galaxies: evolution, (galaxies:) quasars: supermassive black holes}, year = {2025}, month = may, volume = {42}, eid = {e068}, pages = {e068}, doi = {10.1017/pasa.2025.10035}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025PASA...42...68G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, host galaxy, jwst, local counterpart, morphology}, eprint = {2503.10958}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {5} }

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The “Dark-Matter Dominated” Galaxy Segue 1 Modeled with a Black Hole and no Dark Halo

Nathaniel Lujan, Karl Gebhardt, Richard Anantua, and 11 more authors

arXiv e-prints, May 2025

Abs DOI ADS arXiv

The dwarf spheroidal galaxy, Segue 1, is thought to have one of the largest ratios of dark matter to stellar mass. Using orbit-based dynamical models, we model Segue 1, including a dark halo and a central black hole. The best-fit model requires a black hole mass of 4 \pm 1.5 \times 10^5 M_⊙. The value of the black hole mass is the same with or without a dark halo. The mass-to- light ratio of the stars is poorly constrained by the dynamical modeling, reflecting that Segue 1 is dominated by mass other than stars. Dynamical models that exclude a black hole provide a worse fit and require a dark halo with very small scale radii of around 100 parsecs. Additionally, the zero black hole models require a stellar orbital distribution that is highly radially biased. The model with a black hole provides an orbital structure that is close to isotropic, more similar to other well-studied systems. We argue that the two-parameter models of stars and black hole provide a better description of Segue 1 than the three-parameter models of stars and two dark halo components. Additional support for a central black hole comes from a significant increase in the central rotation. Using individual velocities, we measure a rotation amplitude of 9.0 \pm 2.4 \mathrmkm s^-1. Segue 1 is likely being tidally stripped at large radii, and we might be witnessing the remnant nucleus of a more massive system. Alternatively, given the high black hole mass relative to the stellar mass, Segue 1 is analogous to Little Red Dots seen in the early Universe.

@article{2025arXiv250506198L, author = {{Lujan}, Nathaniel and {Gebhardt}, Karl and {Anantua}, Richard and {Chase}, Owen and {Debski}, Maya H. and {Finley}, Claire and {Gomez}, Loraine V. and {Gupta}, Om and {Lawson}, Alex J. and {Marron}, Izabella and {Martinez}, Zorayda and {Painter}, Connor A. and {Sklansky}, Yonatan and {West}, Hayley}, title = {{The ``Dark-Matter Dominated'' Galaxy Segue 1 Modeled with a Black Hole and no Dark Halo}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = may, eid = {arXiv:2505.06198}, pages = {arXiv:2505.06198}, doi = {10.48550/arXiv.2505.06198}, archiveprefix = {arXiv}, eprint = {2505.06198}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250506198L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, kinematics, local counterpart, non-agn, spectroscopy}, month_numeric = {5} }

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“In Brief: ”“Little Red Dots”“ and Early Black Holes”

Hannah Richter

\skytel, May 2025

ADS

@article{2025S&T...149e...9R, author = {{Richter}, Hannah}, title = {{``In Brief: ''``Little Red Dots''`` and Early Black Holes''}}, journal = {\skytel}, year = {2025}, month = may, volume = {149}, number = {5}, pages = {9}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025S\&T...149e...9R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, multi-wavelength, non-agn, theory}, month_numeric = {5} }

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Suppressed Accretion onto Massive Black Hole Binaries Surrounded by Thin Disks

Christopher Tiede, Jonathan Zrake, Andrew MacFadyen, and 1 more author

The Astrophysical Journal, May 2025

Abs DOI ADS arXiv

We demonstrate that gas disks around binary systems might deliver gas to the binary components only when the circumbinary disk is relatively warm. We present new grid-based hydrodynamics simulations, performed with the binary on the grid and a locally isothermal equation of state, in which the binary is seen to functionally “stop accreting” if the orbital Mach number in the disk exceeds a threshold value of about 40. Above this threshold, the disk continues to extract angular momentum from the binary orbit, but it delivers very little mass to the black holes and instead piles up mass in a ring surrounding the binary. This ring will eventually become viscously relaxed and deliver mass to the binary at the large-scale inflow rate. However, we show that the timescale for such relaxation can far exceed the implied binary lifetime. We demonstrate that the ability of a binary–disk system to equilibrate is dependent on the efficiency at which accretion streams deposit mass onto the binary, which, in turn is highly sensitive to the thermodynamic conditions of the inner disk. If disks around massive black hole binaries do operate in such nonaccreting regimes, it suggests these systems may be dimmer than their single black hole counterparts but could exhibit dramatic rebrightening after the black holes inspiral and merge. This dimming begins in the UV/optical and could completely choke high-energy emission, such that these systems would likely be intrinsically X-ray weak with reddened continua, potentially resembling the spectra of “little red dots” recently identified in JWST observations.

@article{2025ApJ...984..144T, author = {{Tiede}, Christopher and {Zrake}, Jonathan and {MacFadyen}, Andrew and {Haiman}, Zolt{\'a}n}, title = {{Suppressed Accretion onto Massive Black Hole Binaries Surrounded by Thin Disks}}, journal = {\apj}, keywords = {Accretion, Active galactic nuclei, Hydrodynamical simulations, Supermassive black holes, 14, 16, 767, 1663, Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = may, volume = {984}, number = {2}, eid = {144}, pages = {144}, doi = {10.3847/1538-4357/adc727}, archiveprefix = {arXiv}, eprint = {2410.03830}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...984..144T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, simulation, theory, x-ray}, month_numeric = {5} }

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Luminous mid-IR-selected type 2 quasars at cosmic noon in SDSS Stripe 82 ─ I. Selection, composite photometry, and spectral energy distributions

Ben Wang, Joseph F. Hennawi, Zheng Cai, and 6 more authors

Monthly Notices of the Royal Astronomical Society, May 2025

Abs DOI ADS arXiv

We analyse 23 spectroscopically confirmed type 2 quasars (QSOs) selected from Wide-field Infrared Survey Explorer 22 band in the Sloan Digital Sky Survey Stripe 82 region, focusing on their multiband photometry and spectral energy distributions (SEDs). The 24 candidates were selected to be infrared (IR) luminous (), optically faint (), or with red colour (). Gemini/Gemini Near- InfraRed Spectrograph and Keck/Low-Resolution Imaging Spectrometer observations confirm 23 to be type 2 QSOs at . Multiband photometry is used for SED fitting, covering 0.1─10 m in the rest frame. The IR emission is dominated by the dust torus, with an average luminosity of . We present three possibilities for the origin of the rest-ultraviolet/optical: scattered light, stellar emission, and the reddened accretion disc. Assuming an obscured:unobscured ratio of 1:1, the targets have bolometric luminosities of and supermassive black hole masses of , averaging and , assuming the Eddington limit. Compared to previous type 2 active galactic nuclei SEDs, our targets have a brighter dust torus and redder optical─IR colour. By comparing the SED to JWST ’little red dots’ (LRDs), we find that these IR-selected type 2 QSOs have similar SED shapes to the LRDs. This survey demonstrates mid-IR selection as an efficient method to find luminous type 2 QSOs and the composite photometry generated by this sample provides a guide for finding more type 2 QSOs at higher redshift in the future.

@article{2025MNRAS.539.1562W, author = {{Wang}, Ben and {Hennawi}, Joseph F. and {Cai}, Zheng and {Richards}, Gordon T. and {Schindler}, Jan-Torge and {Zakamska}, Nadia L. and {Ishikawa}, Yuzo and {Akins}, Hollis B. and {Sun}, Zechang}, title = {{Luminous mid-IR-selected type 2 quasars at cosmic noon in SDSS Stripe 82 ─ I. Selection, composite photometry, and spectral energy distributions}}, journal = {\mnras}, keywords = {galaxies: high-redshift, quasars: emission lines, quasars: general, quasars: supermassive black holes, infrared: galaxies, Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = may, volume = {539}, number = {2}, pages = {1562-1594}, doi = {10.1093/mnras/staf574}, archiveprefix = {arXiv}, eprint = {2501.14026}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.539.1562W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, non-jwst, photometry, sample selection, sed}, month_numeric = {5} }

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RUBIES: JWST/NIRSpec Confirmation of an Infrared-luminous, Broad-line Little Red Dot with an Ionized Outflow

Bingjie Wang, Anna de Graaff, Rebecca L. Davies, and 22 more authors

The Astrophysical Journal, May 2025

Abs DOI ADS arXiv

The JWST discovery of “little red dots” (LRDs) is reshaping our picture of the early Universe, yet the physical mechanisms driving their compact size and UV-optical colors remain elusive. Here, we report an unusually bright LRD (z_spec = 3.1) observed as part of the RUBIES program. This LRD exhibits broad emission lines (FWHM \ensuremath∼ 4000 km s^‑1), a blue UV continuum, a clear Balmer break, and a red continuum sampled out to rest-frame 4 \ensuremathμm with MIRI. We develop a new joint galaxy and active galactic nucleus (AGN) model within the Prospector Bayesian inference framework and perform spectrophotometric modeling using NIRCam, MIRI, and NIRSpec/Prism observations. Our fiducial model reveals a M_* \ensuremath∼ 10^9 M_\ensuremath⊙ galaxy alongside a dust-reddened AGN driving the optical emission. Explaining the rest-frame optical color as a reddened AGN requires A_V \ensuremath≳ 3, suggesting that a great majority of the accretion disk energy is reradiated as dust emission. Yet, despite clear AGN signatures, we find a surprising lack of hot torus emission, which implies that either the dust emission in this object must be cold, or the red continuum must instead be driven by a massive, evolved stellar population of the host galaxy—seemingly inconsistent with the high-EW broad lines (H\ensuremathα rest-frame EW \ensuremath∼ 800 Å). The widths and luminosities of Pa-\ensuremathβ, Pa-\ensuremathδ, Pa-\ensuremathγ, and H\ensuremathα imply a modest black hole mass of M_BH \ensuremath∼ 10^8 M_\ensuremath⊙. Additionally, we identify a narrow blueshifted He I \ensuremathλ 1.083 \ensuremathμm absorption feature in NIRSpec/G395M spectra, signaling an ionized outflow with kinetic energy up to \ensuremath∼1% the luminosity of the AGN. The low redshift of RUBIES-BLAGN-1, combined with the depth and richness of the JWST imaging and spectroscopic observations, provides a unique opportunity to build a physical model for these so-far mysterious LRDs, which may prove to be a crucial phase in the early formation of massive galaxies and their supermassive black holes.

@article{2025ApJ...984..121W, author = {{Wang}, Bingjie and {de Graaff}, Anna and {Davies}, Rebecca L. and {Greene}, Jenny E. and {Leja}, Joel and {Brammer}, Gabriel B. and {Goulding}, Andy D. and {Miller}, Tim B. and {Suess}, Katherine A. and {Weibel}, Andrea and {Williams}, Christina C. and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Cleri}, Nikko J. and {Hirschmann}, Michaela and {Katz}, Harley and {Labb{\'e}}, Ivo and {Maseda}, Michael V. and {Matthee}, Jorryt and {McConachie}, Ian and {Naidu}, Rohan P. and {Oesch}, Pascal A. and {Rix}, Hans-Walter and {Setton}, David J. and {Whitaker}, Katherine E.}, title = {{RUBIES: JWST/NIRSpec Confirmation of an Infrared-luminous, Broad-line Little Red Dot with an Ionized Outflow}}, journal = {\apj}, keywords = {AGN host galaxies, Active galactic nuclei, Galaxy kinematics, Galaxy formation, Photoionization, Spectral energy distribution, 2017, 16, 602, 595, 2060, 2129}, year = {2025}, month = may, volume = {984}, number = {2}, eid = {121}, pages = {121}, doi = {10.3847/1538-4357/adc1ca}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...984..121W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, emission lines, jwst, spectroscopy}, altmetric = {177137995}, eprint = {2403.02304}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {5} }

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Analysis of Multi-epoch JWST Images of \ensuremath∼300 Little Red Dots: Tentative Detection of Variability in a Minority of Sources

Zijian Zhang, Linhua Jiang, Weiyang Liu, and 1 more author

The Astrophysical Journal, May 2025

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has revealed a population of red and compact sources at z \ensuremath≳ 5 known as “little red dots” (LRDs) that are likely active galactic nuclei (AGNs). Here, we present a comprehensive study of the variability of 314 LRDs with multi-epoch JWST observations in five deep fields: Ultra Deep Survey, GOODS-S, GOODS-N, A2744, and COSMOS. Our analyses use all publicly available JWST NIRCam imaging data in these fields, together with multi-epoch JWST MIRI images available. We measure the significance (signal-to- noise ratio or SNR_var) of the variabilities for all LRDs and statistically evaluate their variabilities using the SNR_var distributions. We pay particular attention to the systematic offsets of photometric zero-points among different epochs that seem to commonly exist. The derived SNR_var distributions of the LRDs, including those with broad H\ensuremathα/H\ensuremathβ emission lines, follow the standard Gaussian distribution, and are generally consistent with those of the comparison samples of objects detected in the same images. This finding suggests that the LRD population, on average, does not show strong variability, which can be explained by super-Eddington accretion of the black holes in AGNs. Alternatively, many of them may be dominated by galaxies. We also find eight strongly variable LRD candidates with variability amplitudes of 0.24–0.82 mag. The rest-frame optical spectral energy distributions of these variable LRDs should have a significant AGN contribution. Future JWST observations will provide more variability information on LRDs.

@article{2025ApJ...985..119Z, author = {{Zhang}, Zijian and {Jiang}, Linhua and {Liu}, Weiyang and {Ho}, Luis C.}, title = {{Analysis of Multi-epoch JWST Images of {\ensuremath{\sim}}300 Little Red Dots: Tentative Detection of Variability in a Minority of Sources}}, journal = {\apj}, keywords = {High-redshift galaxies, Active galactic nuclei, 734, 16}, year = {2025}, month = may, volume = {985}, number = {1}, eid = {119}, pages = {119}, doi = {10.3847/1538-4357/adcb3e}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...985..119Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, photometry, sed, variability}, eprint = {2411.02729}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {5} }

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The Host Galaxy (If Any) of the Little Red Dots

Chang-Hao Chen, Luis C. Ho, Ruancun Li, and 1 more author

The Astrophysical Journal, Apr 2025

Abs DOI ADS arXiv

We investigate the host galaxy properties of eight little red dots (LRDs) selected from the JWST UNCOVER survey, applying a new technique (GalfitS) to simultaneously fit the morphology and spectral energy distribution using multiband NIRCam images covering \ensuremath∼1–4 \ensuremathμm. We detect the host galaxy in only one LRD, MSAID38108 at z = 4.96, which has a stellar mass of , an effective radius of kpc, and a Sérsic index of . No host emission centered on the central point source is found in the other seven LRDs. We derive stringent upper limits for the stellar mass of a hypothetical host galaxy by conducting realistic mock simulations that place high-redshift galaxy images under the LRDs. Based on the black hole masses estimated from the broad H\ensuremathα emission line, the derived stellar mass limits are at least a factor of 10 lower than expected from the z \ensuremath≈ 0 scaling relation between black hole mass and host galaxy stellar mass. Intriguingly, four of the LRDs (50% of the sample) show extended, off-centered emission, which is particularly prominent in the bluer bands. The asymmetric emission of two sources can be modeled as stellar emission, but the nature of the other two is unclear.

@article{2025ApJ...983...60C, author = {{Chen}, Chang-Hao and {Ho}, Luis C. and {Li}, Ruancun and {Zhuang}, Ming-Yang}, title = {{The Host Galaxy (If Any) of the Little Red Dots}}, journal = {\apj}, keywords = {Early universe, Galaxy formation, High-redshift galaxies, Active galactic nuclei, AGN host galaxies, 435, 595, 734, 16, 2017, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = apr, volume = {983}, number = {1}, eid = {60}, pages = {60}, doi = {10.3847/1538-4357/ada93a}, archiveprefix = {arXiv}, eprint = {2411.04446}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...983...60C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, host galaxy, jwst, morphology, sed}, month_numeric = {4} }

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Lack of Rest-frame Ultraviolet Variability in Little Red Dots Based on HST and JWST Observations

Wei Leong Tee, Xiaohui Fan, Feige Wang, and 1 more author

The Astrophysical Journal Letters, Apr 2025

Abs DOI ADS arXiv

Variability is a fundamental signature for active galactic nuclei (AGN) activity and serves as an unbiased indicator for rapid instability happening near the center of supermassive black holes (SMBHs). Previous studies showed that AGN variability does not have strong redshift evolution, and scales with their bolometric luminosity and BH mass, making it a powerful probe to identify low-mass, low-luminosity AGNs at high redshift. JWST has discovered a new population of high-redshift galaxies likely hosting moderate accreting BHs (>10^6M_\ensuremath⊙)—the little red dots (LRDs; z \ensuremath∼ 4–10). In this Letter, we study the variability of a sample of 22 LRDs with V-shaped spectral energy distributions in three JWST deep fields that also have reliable Hubble Space Telescope observations in closely paired filters at 1–2 \ensuremathμm (rest-frame UV), with the time difference between 6 and 11 yr. This LRD sample covers a redshift range of 3 < z < 8 with ‑21.3 < M_UV < ‑18.4. Based on both photometry and imaging difference analyses, we find a mean magnitude difference of \ensuremath∼0.15 \ensuremath\pm 0.26 mag, with none of the LRDs showing photometric variability at 3\ensuremathσ significance. Extrapolation of Sloan Digital Sky Survey quasar variability predicts a magnitude change of order 0.3 mag for our LRD sample. This suggests an upper limit of about \ensuremath∼30% AGN contribution to the total observed UV light in our sample of LRDs.

@article{2025ApJ...983L..26T, author = {{Tee}, Wei Leong and {Fan}, Xiaohui and {Wang}, Feige and {Yang}, Jinyi}, title = {{Lack of Rest-frame Ultraviolet Variability in Little Red Dots Based on HST and JWST Observations}}, journal = {\apjl}, keywords = {Active galactic nuclei, Supermassive black holes, Quasars, 16, 1663, 1319, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = apr, volume = {983}, number = {1}, eid = {L26}, pages = {L26}, doi = {10.3847/2041-8213/adc5e3}, archiveprefix = {arXiv}, eprint = {2412.05242}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...983L..26T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, non-agn, sed, variability}, month_numeric = {4} }

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A Quasar-anchored Protocluster at z = 6.6 in the ASPIRE Survey. II. An Environmental Analysis of Galaxy Properties in an Overdense Structure

Jaclyn B. Champagne, Feige Wang, Jinyi Yang, and 21 more authors

The Astrophysical Journal, Mar 2025

Abs DOI ADS arXiv

We present in this paper (Paper II of the series) a 35 arcmin^2 JWST/NIRCam imaging and wide-field slitless spectroscopy mosaic centered on J0305–3150, a luminous quasar at z = 6.61. The F356W grism data reveal 124 [O III]+H\ensuremathβ emitters at 5.3 < z < 7, 53 of which constitute a protocluster spanning (10 cMpc)^2 across 6.5 < z < 6.8. We find no evidence of any broad-line active galactic nucleus (AGN) in individual galaxies or stacking, reporting a median H\ensuremathβ FWHM of 585 \ensuremath\pm 152 km s^‑1; however, the mass–excitation diagram and “little red dot” color and compactness criteria suggest that there are a few AGN candidates on the outskirts of the protocluster. We fit the spectral energy distributions (SEDs) of the [O III] emitters with Prospector and Bagpipes and find that none of the SED-derived properties (stellar mass, age, or star formation rate) correlate with proximity to the quasar. While there is no correlation between galaxy age and local galaxy density, we find modest correlations of local galaxy density with increasing stellar mass, decreasing 10–100 Myr star formation rate ratios, and decreasing nebular line equivalent widths. We further find that the protocluster galaxies are consistent with being more massive, being older, and hosting higher star formation rates than the field sample at the 3\ensuremathσ level, distributed in a filamentary structure that supports inside-out formation of the protocluster. There is modest evidence that galaxy evolution proceeds differently as a function of the density of local environment within protoclusters during the epoch of reionization, and the central quasar has little effect on the galaxy properties of the surrounding structure.

@article{2025ApJ...981..114C, author = {{Champagne}, Jaclyn B. and {Wang}, Feige and {Yang}, Jinyi and {Fan}, Xiaohui and {Hennawi}, Joseph F. and {Sun}, Fengwu and {Ba{\textasciitilde n}ados}, Eduardo and {Bosman}, Sarah E. I. and {Costa}, Tiago and {Habouzit}, Melanie and {Jin}, Xiangyu and {Jun}, Hyunsung D. and {Li}, Mingyu and {Liu}, Weizhe and {Loiacono}, Federica and {Lupi}, Alessandro and {Mazzucchelli}, Chiara and {Pudoka}, Maria and {Rojas-Ruiz}, Sof{\'\i}a and {Tee}, Wei Leong and {Trebitsch}, Maxime and {Zhang}, Haowen and {Zhuang}, Ming-Yang and {Zou}, Siwei}, title = {{A Quasar-anchored Protocluster at z = 6.6 in the ASPIRE Survey. II. An Environmental Analysis of Galaxy Properties in an Overdense Structure}}, journal = {\apj}, keywords = {Galaxy spectroscopy, High-redshift galaxy clusters, Protoclusters, James Webb Space Telescope, AGN host galaxies, AB photometry, Galaxy evolution, 2171, 2007, 1297, 2291, 2017, 2168, 594, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, volume = {981}, number = {2}, eid = {114}, pages = {114}, doi = {10.3847/1538-4357/adb1bc}, archiveprefix = {arXiv}, eprint = {2410.03827}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...981..114C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {clustering, emission lines, jwst, sed, spectroscopy}, month_numeric = {3} }

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SAPPHIRES: A Galaxy Over-Density in the Heart of Cosmic Reionization at z=8.47

Yoshinobu Fudamoto, Jakob M. Helton, Xiaojing Lin, and 17 more authors

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

We report the discovery of a galaxy proto-cluster candidate (dubbed MACS0416-OD-z8p5) at a spectroscopic redshift of z\sim8.47, dating back to \sim550Myr after the Big Bang. The observations are part of the JWST Cycle-3 treasury program, Slitless Areal Pure-Parallel HIgh-Redshift Emission Survey (SAPPHIRES) with NIRCam-grism. Using wide field slitless spectroscopy (WFSS) obtained in the MACS0416 parallel field, we robustly confirm nine galaxies at z_\rm spec\sim8.47 via emission line detections of [OIII]5008A (with >5\,σ) and tentatively confirm one additional galaxy (at \sim3\,σ). This discovery represents the highest-redshift, spectroscopically confirmed galaxy over-density known to date, which is \sim6–8 times more dense than the average volume density of galaxies at the same redshift. Furthermore, a galaxy hosting a low-mass active galactic nucleus (“Little-Red-Dot”) is found as a member, suggesting an early emergence of active, massive black holes and feedback between these black holes and their surrounding environments. We also discuss the spatial structures connecting the galaxy over-density to nearby massive star- forming galaxies (separated by ∼5pMpc, including MACS0416-Y1 and MACS0416-JD. This finding of a massive dark matter halo hosting a galaxy over-density at z\sim8.5 is surprising given that our survey covered only a small, random field (16.5\,\rm arcmin^2) as part of a pure parallel observation. The comparison with cosmological simulations shows that the likelihood of finding such a large-scale structure is <5\,% under the current galaxy formation scenario and the observed survey volume. Our results demonstrate the power of WFSS observations to build a complete line-emitter sample and suggest an important role for over-densities in enhancing galaxy formation by funneling large-scale gas supplies into small cosmological volumes.

@article{2025arXiv250315597F, author = {{Fudamoto}, Yoshinobu and {Helton}, Jakob M. and {Lin}, Xiaojing and {Sun}, Fengwu and {Behroozi}, Peter and {Hsiao}, Tiger Yu-Yang and {Egami}, Eiichi and {Bunker}, Andrew J. and {Harikane}, Yuichi and {Ouchi}, Masami and {Liu}, Yichen and {Liu}, Weizhe and {Maiolino}, Roberto and {Ji}, Zhiyuan and {Jin}, Xiangyu and {Tee}, Wei Leong and {Wang}, Feige and {Willmer}, Christopher N. A. and {Xu}, Yi and {Zhu}, Yongda}, title = {{SAPPHIRES: A Galaxy Over-Density in the Heart of Cosmic Reionization at $z=8.47$}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, eid = {arXiv:2503.15597}, pages = {arXiv:2503.15597}, doi = {10.48550/arXiv.2503.15597}, archiveprefix = {arXiv}, eprint = {2503.15597}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250315597F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {clustering, early universe, emission lines, jwst, spectroscopy}, month_numeric = {3} }

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UNCOVER: 404 Error—Models Not Found for the Triply Imaged Little Red Dot A2744-QSO1

Yilun Ma, Jenny E. Greene, David J. Setton, and 20 more authors

The Astrophysical Journal, Mar 2025

Abs DOI ADS arXiv

JWST has revealed an abundance of compact, red objects at z \ensuremath≈ 5–8 dubbed “little red dots” (LRDs), whose SEDs display a faint blue UV continuum followed by a steep rise in the optical. Despite extensive study of their characteristic V-shaped SEDs, the nature of LRDs remains unknown. We present a new analysis of the NIRSpec/PRISM spectrum of A2744-QSO1, a triply imaged LRD at z = 7.04 from the UNCOVER survey. The spectrum shows a strong Balmer break and broad Balmer emission lines, both of which are difficult to explain with models invoking exclusively AGN or stellar contributions. Our fiducial model decomposes the spectrum into a post-starburst galaxy dominating the UV-optical continuum and a reddened AGN being subdominant at all wavelengths and contributing at a level of \ensuremath∼20%. However, this model infers a stellar mass of M_\ensuremath⋆ \ensuremath≈ 4 \texttimes 10^9 M_\ensuremath⊙ within a radius of r_e < 30 pc, driving its central density to the highest among observations to date. This high central density could be explained if A2744-QSO1 is the early-forming core of a modern-day massive elliptical galaxy that later puffed up via the inside-out growth channel. The models also necessitate an unusually steep dust extinction law to preserve the strong break strength, though this steepness may be explained by a deficit of large dust grains. It is also probable that these challenges reflect our ignorance of A2744-QSO1’s true nature. Future variability and reverberation mapping studies could help disentangle the galaxy and AGN contribution to the continuum, and deeper redder observations could also unveil the dust properties in LRDs. *The error code 404 in the title represents that no satisfying model is found for A2744-QSO 1. In computer network communication, the code “404” refers to the error occurring when the server cannot find the requested information.

@article{2025ApJ...981..191M, author = {{Ma}, Yilun and {Greene}, Jenny E. and {Setton}, David J. and {Volonteri}, Marta and {Leja}, Joel and {Wang}, Bingjie and {Bezanson}, Rachel and {Brammer}, Gabriel and {Cutler}, Sam E. and {Dayal}, Pratika and {van Dokkum}, Pieter and {Furtak}, Lukas J. and {Glazebrook}, Karl and {Goulding}, Andy D. and {de Graaff}, Anna and {Kokorev}, Vasily and {Labbe}, Ivo and {Pan}, Richard and {Price}, Sedona H. and {Weaver}, John R. and {Williams}, Christina C. and {Whitaker}, Katherine E. and {Zitrin}, Adi}, title = {{UNCOVER: 404 Error{\textemdash}Models Not Found for the Triply Imaged Little Red Dot A2744-QSO1}}, journal = {\apj}, keywords = {Active galactic nuclei, Black holes, Galaxy formation, High-redshift galaxies, 16, 162, 595, 734, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2025}, month = mar, volume = {981}, number = {2}, eid = {191}, pages = {191}, doi = {10.3847/1538-4357/ada613}, archiveprefix = {arXiv}, eprint = {2410.06257}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...981..191M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {composite, dust-reddened, jwst, sed, spectroscopy}, month_numeric = {3} }

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A “Black Hole Star” Reveals the Remarkable Gas-Enshrouded Hearts of the Little Red Dots

Rohan P. Naidu, Jorryt Matthee, Harley Katz, and 48 more authors

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

The physical processes that led to the formation of billion solar mass black holes within the first 700 million years of cosmic time remain a puzzle. Several theoretical scenarios have been proposed to seed and rapidly grow black holes, but direct observations of these mechanisms remain elusive. Here we present a source 660 million years after the Big Bang that displays singular properties: among the largest Hydrogen Balmer breaks reported at any redshift, broad multi-peaked Hβemission, and Balmer line absorption in multiple transitions. We model this source as a “black hole star” (BH*) where the Balmer break and absorption features are a result of extremely dense, turbulent gas forming a dust-free “atmosphere” around a supermassive black hole. This source may provide evidence of an early black hole embedded in dense gas – a theoretical configuration proposed to rapidly grow black holes via super- Eddington accretion. Radiation from the BH* appears to dominate almost all observed light, leaving limited room for contribution from its host galaxy. We demonstrate that the recently discovered “Little Red Dots” (LRDs) with perplexing spectral energy distributions can be explained as BH*s embedded in relatively brighter host galaxies. This source provides evidence that black hole masses in the LRDs may be over-estimated by orders of magnitude – the BH* is effectively dust-free contrary to the steep dust corrections applied while modeling LRDs, and the physics that gives rise to the complex line shapes and luminosities may deviate from assumptions underlying standard scaling relations.

@article{2025arXiv250316596N, author = {{Naidu}, Rohan P. and {Matthee}, Jorryt and {Katz}, Harley and {de Graaff}, Anna and {Oesch}, Pascal and {Smith}, Aaron and {Greene}, Jenny E. and {Brammer}, Gabriel and {Weibel}, Andrea and {Hviding}, Raphael and {Chisholm}, John and {Labb\textbackslash'e}, Ivo and {Simcoe}, Robert A. and {Witten}, Callum and {Atek}, Hakim and {Baggen}, Josephine F. W. and {Belli}, Sirio and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Bose}, Sownak and {Covelo-Paz}, Alba and {Dayal}, Pratika and {Fudamoto}, Yoshinobu and {Furtak}, Lukas J. and {Giovinazzo}, Emma and {Goulding}, Andy and {Gronke}, Max and {Heintz}, Kasper E. and {Hirschmann}, Michaela and {Illingworth}, Garth and {Inoue}, Akio K. and {Johnson}, Benjamin D. and {Leja}, Joel and {Leonova}, Ecaterina and {McConachie}, Ian and {Maseda}, Michael V. and {Natarajan}, Priyamvada and {Nelson}, Erica and {Setton}, David J. and {Shivaei}, Irene and {Sobral}, David and {Stefanon}, Mauro and {Tacchella}, Sandro and {Toft}, Sune and {Torralba}, Alberto and {van Dokkum}, Pieter and {van der Wel}, Arjen and {Volonteri}, Marta and {Walter}, Fabian and {Wang}, Bingjie and {Watson}, Darach}, title = {{A ``Black Hole Star'' Reveals the Remarkable Gas-Enshrouded Hearts of the Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics}, year = {2025}, month = mar, eid = {arXiv:2503.16596}, pages = {arXiv:2503.16596}, doi = {10.48550/arXiv.2503.16596}, archiveprefix = {arXiv}, eprint = {2503.16596}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250316596N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, early universe, spectroscopy, super-eddington}, month_numeric = {3} }

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Massive Black Holes Seeded by Dark Matter – Implications for Little Red Dots and Gravitational Wave Signatures

Tingwei Shen, Xuejian Shen, Huangyu Xiao, and 2 more authors

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

Observations of supermassive black holes (SMBHs) at high redshifts challenge standard seeding scenarios. We examine a dissipative self-interacting dark matter (dSIDM) model in which gravothermal collapse leads to the formation of massive BH seeds ab initio. We utilize a semi-analytical framework to predict properties of the dSIDM-seeded SMBH population. Billion solar mass quasars are reproduced along with low-mass faint active galactic nuclei (known as little red dots) with SMBH-to-galaxy stellar mass ratios consistent with recent James Webb Space Telescope observations. To match the abundance of the observed bright quasars, a percent-level duty-cycle is suggested, implying a large population of dormant SMBHs. The gravitational wave (GW) signals from mergers of these massive SMBHs can be detected by LISA while remaining within the NANOGrav constraints on the GW background. These results provide testable signatures of DM- driven SMBH formation, offering a pathway to probe hidden-sector physics through SMBH and GW observables.

@article{2025arXiv250400075S, author = {{Shen}, Tingwei and {Shen}, Xuejian and {Xiao}, Huangyu and {Vogelsberger}, Mark and {Jiang}, Fangzhou}, title = {{Massive Black Holes Seeded by Dark Matter -- Implications for Little Red Dots and Gravitational Wave Signatures}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology}, year = {2025}, month = mar, eid = {arXiv:2504.00075}, pages = {arXiv:2504.00075}, doi = {10.48550/arXiv.2504.00075}, archiveprefix = {arXiv}, eprint = {2504.00075}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250400075S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {exotic physics, heavy seed, jwst, theory}, month_numeric = {3} }

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Exploring active galactic nuclei and little red dots with the Obelisk simulation

M. Volonteri, M. Trebitsch, J. E. Greene, and 8 more authors

Astronomy & Astrophysics, Mar 2025

Abs DOI ADS arXiv

The James Webb Space telescope has discovered an abundant population of broad line emitters, typical signposts for Active Galactic Nuclei (AGN). Many of these sources have red colors and a compact appearance that has led to them being named “little red dots”. In this paper, we develop a detailed framework to estimate the photometry of AGNs embedded in galaxies extracted from the OBELISK cosmological simulation to understand the properties of color-selected little red dots (cLRDs) in the context of the full AGN and massive black hole population. We find that using realistic spectral energy distributions (SEDs) and attenuation for AGNs we can explain the shape of the cLRD SED as long as galaxies host a sufficiently luminous AGN that is neither overly attenuated nor too little attenuated. When attenuation is too low or too high, AGNs do not enter the cLRD selection, because the AGN dominates over the host galaxy too much in blue filters, or it does not contribute to photometry anywhere, respectively. cLRDs are also characterized by high Eddington ratios, possibility super-Eddington ones, and/or high ratios between the black hole and the stellar mass.

@article{2025A&A...695A..33V, author = {{Volonteri}, M. and {Trebitsch}, M. and {Greene}, J. E. and {Dubois}, Y. and {Dong-Paez}, C.-A. and {Habouzit}, M. and {Lupi}, A. and {Ma}, Y. and {Beckmann}, R. S. and {Dayal}, P. and {Schneider}, R.}, title = {{Exploring active galactic nuclei and little red dots with the Obelisk simulation}}, journal = {\aap}, keywords = {black hole physics, galaxies: active, galaxies: high-redshift, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, volume = {695}, eid = {A33}, pages = {A33}, doi = {10.1051/0004-6361/202451963}, archiveprefix = {arXiv}, eprint = {2408.12854}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...695A..33V}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, photometry, sed, simulation, super-eddington}, month_numeric = {3} }

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Strong Rest-UV Emission Lines in a “Little Red Dot” Active Galactic Nucleus at z = 7: Early Supermassive Black Hole Growth alongside Compact Massive Star Formation?

Hollis B. Akins, Caitlin M. Casey, Danielle A. Berg, and 13 more authors

The Astrophysical Journal Letters, Feb 2025

Abs DOI ADS arXiv

JWST has now revealed a population of broad-line active galactic nuclei (AGN) at z \ensuremath≳ 4 characterized by a distinctive spectral energy distribution shape, with a very red rest-frame optical and very blue rest-frame UV continuum. While the optical continuum is thought to originate from the accretion disk, the origin of the UV continuum has been largely unclear. We report the detection of the strong rest-frame UV emission lines of C III] \ensuremathλ\ensuremathλ1907, 1909 and C IV \ensuremathλ\ensuremathλ1549, 1551 in a “little red dot” AGN, COS-66964. Spectroscopically confirmed at z = 7.0371, COS-66964 exhibits broad H\ensuremathα emission (FWHM \ensuremath∼ 2000 km s^‑1) and weak broad H\ensuremathβ, implying significant dust attenuation to the broad-line region (). The H\ensuremathα line width implies a central supermassive black hole (SMBH) mass of M_\ensuremath⊙ and an Eddington ratio \ensuremathλ \ensuremath∼ 0.3–0.5. While marginal He II \ensuremathλ4687 and [Fe X] \ensuremathλ6376 detections further indicate that the AGN dominates in the rest- frame optical, the nondetection of He II \ensuremathλ1640 in the UV despite high EW C III] and C IV (\ensuremath∼35 Å) is more consistent with photoionization by massive stars. The nondetection of Mg II \ensuremathλ\ensuremathλ2800 is similarly inconsistent with an AGN scattered light interpretation. Assuming the rest-frame UV is dominated by stellar light, we derive a stellar mass of , implying an elevated M_BH/M_\ensuremath⋆ ratio \ensuremath∼2 orders of magnitude above the local relation, but consistent with other high-z AGN discovered by JWST. The source is unresolved in all bands, implying a very compact size \ensuremath≲200 pc in the UV. This suggests that the simultaneous buildup of compact stellar populations (i.e., galaxy bulges) and the central SMBH is ongoing even at z \ensuremath≳ 7.

@article{2025ApJ...980L..29A, author = {{Akins}, Hollis B. and {Casey}, Caitlin M. and {Berg}, Danielle A. and {Chisholm}, John and {Cloonan}, Aidan P. and {Franco}, Maximilien and {Finkelstein}, Steven L. and {Fujimoto}, Seiji and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Lambrides}, Erini and {Robertson}, Brant E. and {Taylor}, Anthony J. and {Coulter}, David A. and {Fox}, Ori and {Karmen}, Mitchell}, title = {{Strong Rest-UV Emission Lines in a ``Little Red Dot'' Active Galactic Nucleus at z = 7: Early Supermassive Black Hole Growth alongside Compact Massive Star Formation?}}, journal = {\apjl}, keywords = {AGN host galaxies, Active galactic nuclei, High-redshift galaxies, Reionization, Galaxies, Galaxy evolution, 2017, 16, 734, 1383, 573, 594, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = feb, volume = {980}, number = {2}, eid = {L29}, pages = {L29}, doi = {10.3847/2041-8213/adab76}, archiveprefix = {arXiv}, eprint = {2410.00949}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...980L..29A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst}, month_numeric = {2} }

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Erratum: “The Small Sizes and High Implied Densities of ”Little Red Dots“ with Balmer Breaks Could Explain Their Broad Emission Lines without an Active Galactic Nucleus” (2024, ApJL, 977, L13)

Josephine F. W. Baggen, Pieter van Dokkum, Gabriel Brammer, and 10 more authors

The Astrophysical Journal Letters, Feb 2025

DOI ADS

@article{2025ApJ...980L..47B, author = {{Baggen}, Josephine F. W. and {van Dokkum}, Pieter and {Brammer}, Gabriel and {de Graaff}, Anna and {Franx}, Marijn and {Greene}, Jenny and {Labb{\'e}}, Ivo and {Leja}, Joel and {Maseda}, Michael V. and {Nelson}, Erica J. and {Rix}, Hans-Walter and {Wang}, Bingjie and {Weibel}, Andrea}, title = {{Erratum: ``The Small Sizes and High Implied Densities of ''Little Red Dots`` with Balmer Breaks Could Explain Their Broad Emission Lines without an Active Galactic Nucleus'' (2024, ApJL, 977, L13)}}, journal = {\apjl}, year = {2025}, month = feb, volume = {980}, number = {2}, eid = {L47}, pages = {L47}, doi = {10.3847/2041-8213/adb424}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...980L..47B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, morphology, non-agn, sed, spectroscopy}, month_numeric = {2} }

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An Investigation into the Selection and Colors of Little Red Dots and Active Galactic Nuclei

Kevin N. Hainline, Roberto Maiolino, Ignas Juodžbalis, and 25 more authors

The Astrophysical Journal, Feb 2025

Abs DOI ADS arXiv

Recently, a large number of compact sources at z > 4 with blue UV slopes and extremely red rest-frame optical slopes have been found in James Webb Space Telescope (JWST) extragalactic surveys. As a subsample of these sources, commonly called “little red dots” (LRDs), have been spectroscopically observed to host a broad- line active galactic nucleus (AGN), they have been the focus of multiple recent studies in an attempt to understand the origin of their UV and optical emission. Here, we assemble a sample of 123 LRDs from the literature along with spectroscopic and photometric JWST-identified samples of AGNs to compare their colors and spectral slopes. We find that while obscured AGNs at z 6, the majority of the unobscured AGNs that have been found in these samples are LRDs, but this may be related to the fact that these sources are at large bolometric luminosities. Because LRDs occupy a unique position in galaxy color space, they are more straightforward to target, and the large number of broad-line AGNs that do not have LRD colors and slopes are therefore underrepresented in many spectroscopic surveys because they are more difficult to preselect. Current LRD selection techniques return a large and disparate population, including many sources having 2–5 \ensuremathμm colors impacted by emission- line flux boosting in individual filters.

@article{2025ApJ...979..138H, author = {{Hainline}, Kevin N. and {Maiolino}, Roberto and {Juod{\v{z}}balis}, Ignas and {Scholtz}, Jan and {{\"U}bler}, Hannah and {D'Eugenio}, Francesco and {Helton}, Jakob M. and {Sun}, Yang and {Sun}, Fengwu and {Robertson}, Brant and {Tacchella}, Sandro and {Bunker}, Andrew J. and {Carniani}, Stefano and {Charlot}, Stephane and {Curtis-Lake}, Emma and {Egami}, Eiichi and {Johnson}, Benjamin D. and {Lin}, Xiaojing and {Lyu}, Jianwei and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Rinaldi}, Pierluigi and {Silcock}, Maddie S. and {Venturi}, Giacomo and {Williams}, Christina C. and {Willmer}, Christopher N. A. and {Willott}, Chris and {Zhang}, Junyu and {Zhu}, Yongda}, title = {{An Investigation into the Selection and Colors of Little Red Dots and Active Galactic Nuclei}}, journal = {\apj}, keywords = {Active galactic nuclei, James Webb Space Telescope, 16, 2291, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = feb, volume = {979}, number = {2}, eid = {138}, pages = {138}, doi = {10.3847/1538-4357/ad9920}, archiveprefix = {arXiv}, eprint = {2410.00100}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...979..138H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, early universe, jwst, photometry, sed}, month_numeric = {2} }

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Extremely Dense Gas around Little Red Dots and High-redshift Active Galactic Nuclei: A Nonstellar Origin of the Balmer Break and Absorption Features

Kohei Inayoshi and Roberto Maiolino

The Astrophysical Journal Letters, Feb 2025

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has uncovered low-luminosity active galactic nuclei (AGNs) at high redshifts of z \ensuremath≳ 4–7, powered by accreting black holes with masses of \ensuremath∼10^6‑8 M_\ensuremath⊙. One remarkable distinction of these JWST-identified AGNs, compared to their low-redshift counterparts, is that at least \ensuremath∼20% of them present H\ensuremathα and/or H\ensuremathβ absorption, which must be associated with extremely dense (\ensuremath≳10^9 cm^‑3) gas in the broad- line region or its immediate surroundings. These Balmer absorption features unavoidably imply the presence of a Balmer break caused by the same dense gas. In this Letter, we quantitatively demonstrate that a Balmer break can form in AGN spectra without stellar components, when the accretion disk is heavily embedded in dense neutral gas clumps with densities of \ensuremath∼10^9‑11 cm^‑3, where hydrogen atoms are collisionally excited to the n = 2 states and effectively absorb the AGN continuum at the bluer side of the Balmer limit. The nonstellar origin of a Balmer break offers a potential solution to the large stellar masses and densities inferred for little red dots (LRDs) when assuming that their continuum is primarily due to stellar light. Our calculations indicate that the observed Balmer absorption blueshifted by a few hundred km s^‑1, which suggests the presence of dense outflows in the nucleus at rates exceeding the Eddington value. Other spectral features such as higher equivalent widths of broad H\ensuremathα emission and presence of O I lines observed in high-redshift AGNs including LRDs align with the predicted signatures of a dense super-Eddington accretion disk.

@article{2025ApJ...980L..27I, author = {{Inayoshi}, Kohei and {Maiolino}, Roberto}, title = {{Extremely Dense Gas around Little Red Dots and High-redshift Active Galactic Nuclei: A Nonstellar Origin of the Balmer Break and Absorption Features}}, journal = {\apjl}, keywords = {Galaxy formation, High-redshift galaxies, Quasars, Supermassive black holes, 595, 734, 1319, 1663, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = feb, volume = {980}, number = {2}, eid = {L27}, pages = {L27}, doi = {10.3847/2041-8213/adaebd}, archiveprefix = {arXiv}, eprint = {2409.07805}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...980L..27I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, agn-dominated, early universe, jwst, super-eddington}, month_numeric = {2} }

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Radio emission from little red dots may reveal their true nature

Muhammad A. Latif, Ammara Aftab, Daniel J. Whalen, and 1 more author

Astronomy & Astrophysics, Feb 2025

Abs DOI ADS arXiv

Context. The unprecedented sensitivity of the James Webb Space Telescope (JWST) has revolutionized our understanding of the early Universe. Among the most intriguing JWST discoveries are red, very compact objects that show broad line emission features, nicknamed little red dots (LRDs). The discovery of LRDs has triggered great interest in their origin as either extremely starbursting galaxies or highly obscured active galactic nuclei (AGNs). Their exact nature remains unknown. Aims. The goal of this work is to estimate the radio emission from LRDs and predict which radio surveys would detect them. To achieve these objectives, we employed the fundamental plane of black hole (BH) accretion to estimate radio emission from AGNs and the stellar radio fluxes from their host galaxies. We assumed a range of BH masses, X-ray luminosities (L_X), and star formation rates (SFRs) to bracket the likely properties of LRDs. Methods. Our findings suggest that BH radio fluxes from LRDs are 10–100 times higher than the stellar fluxes from their host galaxies, depending on the BH mass, L_X, and SFR. The detection of a \ensuremath∼500 nJy signal above 2 GHz at z \ensuremath≥ 5 or a \ensuremath∼2000 nJy flux at z = 3–4 would be a smoking gun for the presence of AGNs provided that SFRs in the host galaxies are < 30 M_\ensuremath⊙ yr^‑1. Results. We find that LRDs are most likely radio-quiet AGNs; otherwise, they would have already been detected in the current radio surveys. Our findings suggest that LRDs can be detected with upcoming radio observatories such as ngVLA and SKA with integration times of 10–100 h, respectively.

@article{2025A&A...694L..14L, author = {{Latif}, Muhammad A. and {Aftab}, Ammara and {Whalen}, Daniel J. and {Mezcua}, Mar}, title = {{Radio emission from little red dots may reveal their true nature}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2025}, month = feb, volume = {694}, eid = {L14}, pages = {L14}, doi = {10.1051/0004-6361/202453194}, archiveprefix = {arXiv}, eprint = {2502.03742}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...694L..14L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, early universe, jwst, radio}, month_numeric = {2} }

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Discovery of Local Analogs to JWST’s Little Red Dots

Ruqiu Lin, Zhen-Ya Zheng, Chunyan Jiang, and 12 more authors

The Astrophysical Journal Letters, Feb 2025

Abs DOI ADS arXiv

Recently, the James Webb Space Telescope has revealed a new class of high-redshift (high-z, z > 4) compact galaxies that are red in the rest-frame optical and blue in the rest-frame UV with V-shaped spectral energy distributions (SEDs), referred to as “little red dots” (LRDs). It is very likely that LRDs host obscured broad-line active galactic nuclei (AGNs). In the meanwhile, Green Pea galaxies (GPs), which are compact dwarf galaxies at low redshift, share various similar properties with high-redshift star-forming galaxies. Here, we aim to find the connection between the LRDs and GPs hosting broad-line AGNs (BLGPs). With a sample of 19 BLGPs obtained from our previous work, we further identify seven GPs with V-shaped rest-frame UV- to-optical SEDs that are likely local analogs to LRDs. These V-shaped BLGPs exhibit faint UV absolute magnitudes and sub- Eddington rates similar to those of LRDs. Three of them occupy a similar region to LRDs in the Baldwin–Philips–Terlevich diagram, suggesting they have similar ionization conditions and gas-phase metallicities to LRDs. These similarities suggest that V-shaped BLGPs can be taken as local analogs of high-redshift LRDs. In addition, most (16/19) BLGPs, including six V-shaped BLGPs, host overmassive black holes (BHs) above the local M_BH–M_* relation, making it the first sample of galaxies hosting overmassive BHs at z < 0.4. These findings will help us learn more about the formation and coevolution of early galaxies and BHs.

@article{2025ApJ...980L..34L, author = {{Lin}, Ruqiu and {Zheng}, Zhen-Ya and {Jiang}, Chunyan and {Yuan}, Fang-Ting and {Ho}, Luis C. and {Wang}, Junxian and {Jiang}, Linhua and {Rhoads}, James E. and {Malhotra}, Sangeeta and {Barrientos}, L. Felipe and {Wold}, Isak and {Infante}, Leopoldo and {Zhu}, Shuairu and {Ji}, Xiang and {Fu}, Xiaodan}, title = {{Discovery of Local Analogs to JWST's Little Red Dots}}, journal = {\apjl}, keywords = {Emission line galaxies, Extragalactic astronomy, Supermassive black holes, 459, 506, 1663, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = feb, volume = {980}, number = {2}, eid = {L34}, pages = {L34}, doi = {10.3847/2041-8213/adaaf1}, archiveprefix = {arXiv}, eprint = {2412.08396}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...980L..34L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, emission lines, local counterpart, sed}, month_numeric = {2} }

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Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows

Zhengrong Li, Kohei Inayoshi, Kejian Chen, and 2 more authors

The Astrophysical Journal, Feb 2025

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) observations have revolutionized extragalactic research, particularly with the discovery of little red dots (LRDs), which have been discovered as a population of dust-reddened broad-line active galactic nuclei (AGNs). Their unique V-shaped spectral feature, characterized by a red optical continuum and a UV excess in the rest frame, challenges us to discern the relative contributions of the galaxy and AGN. We study a spectral energy distribution (SED) model for LRDs from rest-frame UV to infrared bands. We hypothesize that the incident radiation from an AGN, characterized by a typical SED, is embedded in an extended dusty medium with an extinction law similar to those seen in dense regions such as Orion Nebula or certain AGN environments. The UV‑optical spectrum is described by dust-attenuated AGN emission, featuring a red optical continuum at \ensuremathλ > 4000 Å and a flat UV spectral shape established through a gray extinction curve at \ensuremathλ < 3000 Å, due to the absence of small-size grains. There is no need for additional stellar emission or AGN scattered light. In the infrared, the SED is shaped by an extended dust and gas distribution (\ensuremathγ < 1; \ensuremathρ \ensuremath∝ r^‑\ensuremathγ) with characteristic gas densities of ≃10–10^3 cm^‑3, which allows relatively cool dust temperatures to dominate the radiation. As a result, these dust structures shift the emission energy peak from near-infrared to mid-infrared bands in the rest frame; for sources at z \raisebox-0.5ex~4–7, the corresponding wavelengths shift from the JWST/MIRI to Herschel range. This model, unlike the typical AGN hot torus models, can produce an infrared SED flattening that is consistent with LRD observations through JWST MIRI. Such a density structure can arise from the coexistence of inflows and outflows during the early assembly of galactic nuclei. This might be the reason why LRDs emerge preferentially in the high-redshift Universe younger than 1 billion years.

@article{2025ApJ...980...36L, author = {{Li}, Zhengrong and {Inayoshi}, Kohei and {Chen}, Kejian and {Ichikawa}, Kohei and {Ho}, Luis C.}, title = {{Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows}}, journal = {\apj}, keywords = {Supermassive black holes, Galaxy formation, High-redshift galaxies, Quasars, 1663, 595, 734, 1319, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = feb, volume = {980}, number = {1}, eid = {36}, pages = {36}, doi = {10.3847/1538-4357/ada5fb}, archiveprefix = {arXiv}, eprint = {2407.10760}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...980...36L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, dust-reddened, early universe, jwst, sed}, month_numeric = {2} }

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Three Brown Dwarfs Masquerading as High-redshift Galaxies in JWST Observations

Zhijun Tu, Shu Wang, Xiaodian Chen, and 1 more author

The Astrophysical Journal, Feb 2025

Abs DOI ADS arXiv

We report the spectroscopic identification of three brown dwarf candidates—o005_s41280, o006_s00089, and o006_s35616—discovered in RUBIES using James Webb Space Telescope (JWST) Near-Infrared Spectrograph PRISM/CLEAR spectroscopy. We fit these sources with multiple substellar atmosphere models and present the atmospheric parameters, including effective temperature (T_eff), surface gravity, and other derived properties. The results suggest that o005_s41280 and o006_s35616, with T_eff in the ranges of 2100–2300 K and 1800–2000 K, respectively, are likely L dwarfs, while o006_s00089, with T_eff < 1000 K, is consistent with a late T dwarf classification. The best-fit model spectra provide a reasonable match to the observed spectra. However, distinct residuals exist in the Y, J, and H bands for the two L dwarf candidates, particularly for o006_s35616. Incorporating the extinction parameter into the fitting process can significantly reduce these residuals. The distance estimates indicate that these candidates are about 2 kpc away. The analysis of the color–color diagram using multiple JWST NIRcam photometry suggests that cooler T dwarfs, such as o006_s00089, overlap with little red dots, while hotter L dwarfs, like o005_s41280 and o006_s35616, tend to contaminate the high- redshift galaxy cluster. These findings suggest a brown dwarf contamination rate of approximately 0.1% in extragalactic deep field surveys, with L dwarfs being more frequently detected than cooler T and Y dwarfs.

@article{2025ApJ...980..230T, author = {{Tu}, Zhijun and {Wang}, Shu and {Chen}, Xiaodian and {Liu}, Jifeng}, title = {{Three Brown Dwarfs Masquerading as High-redshift Galaxies in JWST Observations}}, journal = {\apj}, keywords = {Brown dwarfs, L dwarfs, T dwarfs, Stellar atmospheres, High-redshift galaxies, 185, 894, 1679, 1584, 734, Astrophysics - Solar and Stellar Astrophysics}, year = {2025}, month = feb, volume = {980}, number = {2}, eid = {230}, pages = {230}, doi = {10.3847/1538-4357/adaf9f}, archiveprefix = {arXiv}, eprint = {2501.16648}, primaryclass = {astro-ph.SR}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...980..230T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, jwst, non-agn, photometry, spectroscopy}, month_numeric = {2} }

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The self-attractive ultralight axion and its time scale of collapsing in general relativistic framework

Takeshi Fukuyama

\jcap, Jan 2025

Abs DOI ADS arXiv

The formation of supermassive black holes (SMBHs) at high redshift z by ultralight axion dark matter (DM) is discussed in the general relativistic framework. The critical condition of collapsing of self-attracting DM in non-relativistic treatment corresponds to dust particle, which allows to estimate the time scale of the SMBH formation and the its length scale in the general relativistic framework. It gives the support of ultralight axion model based on the string model as the origins of the early universe SMBH and the Little Red Dots (LRDs) etc. observed by James Webb Space Telescope (JWST).

@article{2025JCAP...01..151F, author = {{Fukuyama}, Takeshi}, title = {{The self-attractive ultralight axion and its time scale of collapsing in general relativistic framework}}, journal = {\jcap}, keywords = {axions, dark matter theory, GR black holes, primordial black holes, High Energy Physics - Phenomenology}, year = {2025}, month = jan, volume = {2025}, number = {1}, eid = {151}, pages = {151}, doi = {10.1088/1475-7516/2025/01/151}, archiveprefix = {arXiv}, eprint = {2410.16536}, primaryclass = {hep-ph}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025JCAP...01..151F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, exotic physics, jwst, theory}, month_numeric = {1} }

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EPOCHS. IV. SED Modeling Assumptions and Their Impact on the Stellar Mass Function at 6.5 \ensuremath≤ z \ensuremath≤ 13.5 Using PEARLS and Public JWST Observations

Thomas Harvey, Christopher J. Conselice, Nathan J. Adams, and 31 more authors

The Astrophysical Journal, Jan 2025

Abs DOI ADS arXiv

We utilize deep JWST Near Infrared Camera (NIRCam) observations for the first direct constraints on the Galaxy Stellar Mass Function (GSMF) at z > 10. Our EPOCHS v1 sample includes 1120 galaxy candidates at 6.5 < z < 13.5 taken from a consistent reduction and analysis of publicly available deep JWST NIRCam data covering the Prime Extragalactic Areas for Reionization Science, CEERS, GLASS, JADES GOOD-S, NGDEEP, and SMACS0723 surveys, totaling 187 arcmin^2. We investigate the impact of spectral energy distribution fitting methods, assumed star formation histories (SFHs), dust laws, and priors on galaxy masses and the resultant GSMF. While our fiducial GSMF agrees with the literature at z < 13.5, we find that the assumed SFH model has a large impact on the GSMF and stellar mass density (SMD), finding a 0.75 dex increase in the SMD at z = 10.5 between a flexible nonparametric and standard parametric SFH. Overall, we find a flatter SMD evolution at z \ensuremath≥ 9 than some studies predict, suggesting a rapid buildup of stellar mass in the early Universe. We find no incompatibility between our results and those of standard cosmological models, as suggested previously, although the most massive galaxies may require a high star formation efficiency. We find that the “little red dot” galaxies dominate the z = 7 GSMF at high masses, necessitating a better understanding of the relative contributions of active galactic nucleus and stellar emission. We show that assuming a theoretically motivated top-heavy initial mass function (IMF) reduces stellar mass by 0.5 dex without affecting fit quality, but our results remain consistent with existing cosmological models with a standard IMF.

@article{2025ApJ...978...89H, author = {{Harvey}, Thomas and {Conselice}, Christopher J. and {Adams}, Nathan J. and {Austin}, Duncan and {Juod{\v{z}}balis}, Ignas and {Trussler}, James and {Li}, Qiong and {Ormerod}, Katherine and {Ferreira}, Leonardo and {Lovell}, Christopher C. and {Duan}, Qiao and {Westcott}, Lewi and {Harris}, Honor and {Bhatawdekar}, Rachana and {Coe}, Dan and {Cohen}, Seth H. and {Caruana}, Joseph and {Cheng}, Cheng and {Driver}, Simon P. and {Frye}, Brenda and {Furtak}, Lukas J. and {Grogin}, Norman A. and {Hathi}, Nimish P. and {Holwerda}, Benne W. and {Jansen}, Rolf A. and {Koekemoer}, Anton M. and {Marshall}, Madeline A. and {Nonino}, Mario and {Vijayan}, Aswin P. and {Wilkins}, Stephen M. and {Windhorst}, Rogier and {Willmer}, Christopher N. A. and {Yan}, Haojing and {Zitrin}, Adi}, title = {{EPOCHS. IV. SED Modeling Assumptions and Their Impact on the Stellar Mass Function at 6.5 {\ensuremath{\leq}} z {\ensuremath{\leq}} 13.5 Using PEARLS and Public JWST Observations}}, journal = {\apj}, keywords = {Galaxy counts, High-redshift galaxies, Lyman-break galaxies, Galaxy photometry, Galaxy masses, 588, 734, 979, 611, 607, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = jan, volume = {978}, number = {1}, eid = {89}, pages = {89}, doi = {10.3847/1538-4357/ad8c29}, archiveprefix = {arXiv}, eprint = {2403.03908}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...978...89H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, early universe, jwst, sed, starburst}, month_numeric = {1} }

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The Soltan argument at redshift 6: UV-luminous quasars contribute less than 10% to early black hole mass growth

Knud Jahnke

The Open Journal of Astrophysics, Jan 2025

Abs DOI ADS arXiv

We combine stellar mass functions and the recent first JWST-based galaxy-black hole scaling relations at z=6 to for the first time compute the supermassive black hole (SMBH) mass volume density at this epoch, and compare this to the integrated SMBH mass growth from the population of UV-luminous quasars at z>6. We show that even under very conservative assumptions almost all growth of SMBH mass at z>6 does not take place in these UV- luminous quasars, but must occur in systems obscured through dust and/or with lower radiative efficiency than standard thin accretion disks. The ’Soltan argument’ is not fulfilled by the known population of bright quasars at z>6: the integrated SMBH mass growth inferred from these largely unobscured active galactic nuclei (AGN) in the early Universe is by a factor $$10 smaller than the total SMBH mass volume density at z=6. This is valid under a large range of assumption about luminosity, mass functions, and accretion modes, and is likely still a factor >2 smaller when accounting for known obscuration fractions at this epoch. The resulting consequences are: >90%, possibly substantially more, of SMBH-buildup in the early Universe does not take place in luminous unobscured quasar phases, but has to occur in obscured systems, with dust absorbing most of the emitted UV-visible AGN emission, potentially with accretion modes with super-Eddington specific accretion rates. This is consistent with short lifetimes for luminous quasar phases from quasar proximity zone studies and clustering. This would remove the empirical need for slow SMBH growth and hence exotic ’high- mass seed’ black holes at early cosmic time. It also predicts a large population of luminous but very obscured lower-mass quasars at z>6, possibly the JWST ’Little Red Dots’.

@article{2025OJAp....8E...9J, author = {{Jahnke}, Knud}, title = {{The Soltan argument at redshift 6: UV-luminous quasars contribute less than 10\% to early black hole mass growth}}, journal = {The Open Journal of Astrophysics}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = jan, volume = {8}, eid = {9}, pages = {9}, doi = {10.33232/001c.129063}, archiveprefix = {arXiv}, eprint = {2411.03184}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025OJAp....8E...9J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, early universe, obscuration, super-eddington}, month_numeric = {1} }

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UNCOVER: Candidate Red Active Galactic Nuclei at 3 < z < 7 with JWST and ALMA

Ivo Labbe, Jenny E. Greene, Rachel Bezanson, and 29 more authors

The Astrophysical Journal, Jan 2025

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) is revolutionizing our knowledge of z > 5 galaxies and their actively accreting black holes. Using the JWST Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization (UNCOVER) in the lensing field A2744, we report the identification of a sample of little red dots at 3 \ensuremath≈ 50 pc after correction for magnification), red rest-frame optical slopes, and hot dust can be explained by reddened broad-line active galactic nuclei (AGNs). Our targets have faint M _1450 \ensuremath≈ ‑14 to ‑18 mag but inferred bolometric luminosities of L _bol = 10^43–10^46 erg s^‑1, reflecting their obscured nature. If the candidates are confirmed as AGNs with upcoming UNCOVER spectroscopy, then we have found an abundant population of reddened luminous AGNs that are at least ten times more numerous than UV-luminous AGNs at the same intrinsic bolometric luminosity.

@article{2025ApJ...978...92L, author = {{Labbe}, Ivo and {Greene}, Jenny E. and {Bezanson}, Rachel and {Fujimoto}, Seiji and {Furtak}, Lukas J. and {Goulding}, Andy D. and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Oesch}, Pascal A. and {Atek}, Hakim and {Brammer}, Gabriel and {Chemerynska}, Iryna and {Coe}, Dan and {Cutler}, Sam E. and {Dayal}, Pratika and {Feldmann}, Robert and {Franx}, Marijn and {Glazebrook}, Karl and {Leja}, Joel and {Maseda}, Michael and {Marchesini}, Danilo and {Nanayakkara}, Themiya and {Nelson}, Erica J. and {Pan}, Richard and {Papovich}, Casey and {Price}, Sedona H. and {Suess}, Katherine A. and {Wang}, Bingjie and {Weaver}, John R. and {Whitaker}, Katherine E. and {Williams}, Christina C. and {Zitrin}, Adi}, title = {{UNCOVER: Candidate Red Active Galactic Nuclei at 3 < z < 7 with JWST and ALMA}}, journal = {\apj}, keywords = {AGN host galaxies, Galaxies, 2017, 573, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = jan, volume = {978}, number = {1}, eid = {92}, pages = {92}, doi = {10.3847/1538-4357/ad3551}, archiveprefix = {arXiv}, eprint = {2306.07320}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...978...92L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, alma, dust-reddened, jwst, sed}, month_numeric = {1} }

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Deep silence: Radio properties of little red dots

K. Perger, J. Fogasy, S. Frey, and 1 more author

Astronomy & Astrophysics, Jan 2025

Abs DOI ADS arXiv

To investigate the radio properties of the recently found high-redshift population, we collected a sample of 919 little red dots (LRDs) from the literature. By cross-matching their co-ordinates with the radio catalogues based on the first- and second-epoch observations of the Very Large Array Sky Survey (VLASS) and the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey, we found no radio counterparts coinciding with any of the LRDs. To uncover possible sub-milli-Jansky-level weak radio emission, we performed mean and median image stacking analyses of empty-field ’quick look’ VLASS and FIRST image cutouts centred on the LRD positions. We found no radio emission above 3\ensuremathσ noise levels (\ensuremath∼11 and \ensuremath∼18 \ensuremathμJy beam^‑1 for the VLASS and FIRST maps, respectively) in either of the stacked images for the LRD sample, while the noise levels of the single- epoch images are comparable to those found earlier in the stacking of high-redshift radio-quiet active galactic nuclei (AGNs). The non-detection of radio emission in LRDs suggests that these sources host weaker (or no) radio AGNs.

@article{2025A&A...693L...2P, author = {{Perger}, K. and {Fogasy}, J. and {Frey}, S. and {Gab{\'a}nyi}, K. {\'E}.}, title = {{Deep silence: Radio properties of little red dots}}, journal = {\aap}, keywords = {methods: data analysis, galaxies: active, galaxies: high-redshift, galaxies: star formation, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = jan, volume = {693}, eid = {L2}, pages = {L2}, doi = {10.1051/0004-6361/202452422}, archiveprefix = {arXiv}, eprint = {2411.19518}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...693L...2P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {catalog, early universe, non-agn, radio}, month_numeric = {1} }

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Ultradiffuse Dwarf Galaxies Hosting Pseudobulges

Yu Rong, Hong-Xin Zhang, Cheng Cheng, and 5 more authors

The Astrophysical Journal Letters, Jan 2025

Abs DOI ADS arXiv

By analyzing data from DESI Legacy Imaging Survey of the dwarf galaxies in the Arecibo Legacy Fast Alfa Survey, we have identified five ultradiffuse galaxies (UDGs) featuring central pseudobulges. These UDGs display blue pseudobulges with Sérsic indices n < 2.5 and effective radii spanning 300–700 pc, along with bluer thin stellar disks exhibiting low surface brightness and expansive effective radii that align with the UDG definition. The rotation velocities of these UDGs, determined using H I line widths and optical inclinations, exceed those of most dwarf galaxies of similar mass, suggesting the high halo spins or substantial dark matter halos. We propose that these UDGs likely formed through mergers of dwarf galaxies lacking old stars in their progenitors, resulting in the development of central bulge-like structures during starbursts triggered by the mergers while also enhancing their halo spin. Subsequent gas accretion facilitated the formation of extended stellar disks. It is also worth noting the possibility that these UDGs could alternatively represent “failed L^\ensuremath⋆ galaxies” with massive dark matter halos but reduced star formation efficiencies. If future high-resolution H I observations confirm the presence of massive halos around these UDGs, they may have formed due to intense AGN feedback in the early Universe and may be the descendants of “little red dots” observed by the James Webb Space Telescope, which are characterized by heightened central black hole masses and intensified accretion and feedback processes in the early Universe.

@article{2025ApJ...978L..44R, author = {{Rong}, Yu and {Zhang}, Hong-Xin and {Cheng}, Cheng and {Guo}, Qi and {Ding}, Weiyu and {Hua}, Zichen and {Wang}, Huiyuan and {Kong}, Xu}, title = {{Ultradiffuse Dwarf Galaxies Hosting Pseudobulges}}, journal = {\apjl}, keywords = {Dwarf galaxies, Photometry, Galaxy formation, Galaxy evolution, 416, 1234, 595, 594, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = jan, volume = {978}, number = {2}, eid = {L44}, pages = {L44}, doi = {10.3847/2041-8213/ad9ea6}, archiveprefix = {arXiv}, eprint = {2412.10759}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...978L..44R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, kinematics, morphology, starburst}, month_numeric = {1} }

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2024

Evaluating the Predictive Capacity of FLARES Simulations for High Redshift “Little Red Dots”

Louis M. T. Arts

arXiv e-prints, Dec 2024

Abs DOI ADS arXiv

The recent discovery of little red dots - a population of extremely compact and highly dust-reddened high redshift galaxies - by the James Webb Space Telescope presents a new challenge to the fields of astrophysics and cosmology. Their remarkably high luminosities at redshifts 5 < z < 10, appear to challenge LambdaCDM cosmology and galaxy formation models, as they imply stellar masses and star formation rates that exceed the upper limits set by these models. LRDs are currently subjects of debate as the mechanisms behind their high luminosities are not yet fully understood. LRD energy outputs are thought to be either dominated by star formation or their energy output results from the hosting of active galactic nuclei. We investigate the starburst hypothesis by attempting to replicate the stellar properties of LRDs using output data from the FLARES simulation suite. Comparative analysis of galactic properties such as galactic number density, stellar mass and star formation rate yield significant tension between simulated and observed galaxies. The FLARES simulation overestimates the number densities of galaxies with stellar masses similar to observed LRDs by several orders of magnitude. Additionally, the simulation shows an overestimation of star formation rates. These tensions suggest a potential underestimation by the FLARES model of stellar feedback mechanisms such as active galactic nuclei feedback. These results suggest that the starburst hypothesis may be insufficient to explain the observed properties of these galaxies. Instead, the AGN scenario should be further investigated by repeating the methods in this study with a hydrodynamic galaxy simulation suite that models a higher influence of AGN feedback mechanisms on stellar activity in high redshift galaxies.

@article{2024arXiv241205946A, author = {{Arts}, Louis M. T.}, title = {{Evaluating the Predictive Capacity of FLARES Simulations for High Redshift ``Little Red Dots''}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = dec, eid = {arXiv:2412.05946}, pages = {arXiv:2412.05946}, doi = {10.48550/arXiv.2412.05946}, archiveprefix = {arXiv}, eprint = {2412.05946}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241205946A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, agn-dominated, early universe, simulation, starburst}, month_numeric = {12} }

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The Small Sizes and High Implied Densities of “Little Red Dots” with Balmer Breaks Could Explain Their Broad Emission Lines without an Active Galactic Nucleus

Josephine F. W. Baggen, Pieter van Dokkum, Gabriel Brammer, and 10 more authors

The Astrophysical Journal Letters, Dec 2024

Abs DOI ADS arXiv

Early JWST studies found an apparent population of massive, compact galaxies at redshifts z \ensuremath≳ 7. Recently three of these galaxies were shown to have prominent Balmer breaks, demonstrating that their light at \ensuremathλ_rest \ensuremath∼ 3500 Å is dominated by a stellar population that is relatively old (\ensuremath∼200 Myr). All three also have broad H\ensuremathβ emission with \ensuremathσ > 1000 km s^‑1, a common feature of such “little red dots.” From Sérsic profile fits to the Near Infrared Camera images in F200W we find that the stellar light of galaxies is extremely compact: the galaxies have half-light radii of r_e \ensuremath∼ 100 pc, in the regime of ultracompact dwarfs in the nearby Universe. Their masses are uncertain, as they depend on the contribution of possible light from an active galactic nucleus (AGN) to the flux at \ensuremathλ_rest > 5000 Å. If the AGN contribution is low beyond the Balmer break region, the masses are M_* \ensuremath∼ 10^10–10^11 M_☉, and the central densities are higher than those of any other known galaxy population by 1 order of magnitude. Interestingly, the implied velocity dispersions of \ensuremath∼1500 km s^‑1 are in very good agreement with the measured H\ensuremathβ line widths. We suggest that some of the broad lines in “little red dots” are not due to AGNs, but simply reflect the kinematics of the galaxies, and speculate that the galaxies are observed in a short-lived phase where the central densities are much higher than at later times. We stress, however, that the canonical interpretation of AGNs causing the broad H\ensuremathβ lines also remains viable.

@article{2024ApJ...977L..13B, author = {{Baggen}, Josephine F. W. and {van Dokkum}, Pieter and {Brammer}, Gabriel and {de Graaff}, Anna and {Franx}, Marijn and {Greene}, Jenny and {Labb{\'e}}, Ivo and {Leja}, Joel and {Maseda}, Michael V. and {Nelson}, Erica J. and {Rix}, Hans-Walter and {Wang}, Bingjie and {Weibel}, Andrea}, title = {{The Small Sizes and High Implied Densities of ``Little Red Dots'' with Balmer Breaks Could Explain Their Broad Emission Lines without an Active Galactic Nucleus}}, journal = {\apjl}, keywords = {Galaxies, High-redshift galaxies, Compact galaxies, Galaxy spectroscopy, Active galaxies, Galactic and extragalactic astronomy, 573, 734, 285, 2171, 17, 563, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = dec, volume = {977}, number = {1}, eid = {L13}, pages = {L13}, doi = {10.3847/2041-8213/ad90b8}, archiveprefix = {arXiv}, eprint = {2408.07745}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...977L..13B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, kinematics, morphology, non-agn}, month_numeric = {12} }

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JWST sees little red dots

May Chiao

Nature Reviews Physics, Dec 2024

Abs DOI ADS

With its capability to observe faint objects from the distant past, JWST is discovering objects that were thought to be rare; for example, compact objects that appear as little red dots are more than they seem.

@article{2024NatRP...6..713C, author = {{Chiao}, May}, title = {{JWST sees little red dots}}, journal = {Nature Reviews Physics}, year = {2024}, month = dec, volume = {6}, number = {12}, pages = {713-713}, doi = {10.1038/s42254-024-00789-y}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024NatRP...6..713C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, dust-reddened, early universe, jwst}, month_numeric = {12} }

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An unambiguous AGN and a Balmer break in an Ultraluminous Little Red Dot at z=4.47 from Ultradeep UNCOVER and All the Little Things Spectroscopy

Ivo Labbe, Jenny E. Greene, Jorryt Matthee, and 37 more authors

arXiv e-prints, Dec 2024

Abs DOI ADS arXiv

We present a detailed exploration of the most optically-luminous Little Red Dot (L_Hα=10^44erg/s, L_V=10^45erg/s, F444W=22AB) found to date. Located in the Abell 2744 field, source A744-45924 was observed by NIRSpec/PRISM with ultradeep spectroscopy reaching SNR\sim100pix^-1, high-resolution 3-4 micron NIRCam/Grism spectroscopy, and NIRCam Medium Band imaging. The NIRCam spectra reveal high rest-frame EW W_Hα,0,broad>800Å, broad Hαemission (FWHM\sim4500 km/s), on top of narrow, complex absorption. NIRSpec data show exceptionally strong rest-frame UV to NIR Fe II emission (W_FeII-UV,0\sim340Å), N IV]PLACEHOLDERlambdaPLACEHOLDERlambda1483,1486 and N III]\lambda1750, and broad NIR O I \lambda8446 emission. The spectra unambiguously demonstrate a broad-line region associated with an inferred M_BH\sim10^9M_⊙supermassive black hole embedded in dense gas, which might explain a non-detection in ultradeep Chandra X-ray data (>10\times underluminous relative to broad L_Hα). Strong UV Nitrogen lines suggest supersolar N/O ratios due to rapid star formation or intense radiation near the AGN. The continuum shows a clear Balmer break at rest-frame 3650Å, which cannot be accounted for by an AGN power-law alone. A stellar population model produces an excellent fit with a reddened Balmer break and implying a massive (M_*\sim8\times10^10M_⊙), old \sim500 Myr, compact stellar core, among the densest stellar systems known (PLACEHOLDERrhoPLACEHOLDERsim3\times10^6M_⊙/pc^2 for R_e,opt=70\pm10 pc), and AGN emission with extreme intrinsic EW W_Hα,0\gg1000Å. However, although high M_* and M_BH are supported by evidence of an overdensity containing 40 galaxies at z=4.41-4.51, deep high-resolution spectroscopy is required to confirm stellar absorption and rule out that dense gas around the AGN causes the Balmer break instead.

@article{2024arXiv241204557L, author = {{Labbe}, Ivo and {Greene}, Jenny E. and {Matthee}, Jorryt and {Treiber}, Helena and {Kokorev}, Vasily and {Miller}, Tim B. and {Kramarenko}, Ivan and {Setton}, David J. and {Ma}, Yilun and {Goulding}, Andy D. and {Bezanson}, Rachel and {Naidu}, Rohan P. and {Williams}, Christina C. and {Atek}, Hakim and {Brammer}, Gabriel and {Cutler}, Sam E. and {Chemerynska}, Iryna and {Cloonan}, Aidan P. and {Dayal}, Pratika and {de Graaff}, Anna and {Fudamoto}, Yoshinobu and {Fujimoto}, Seiji and {Furtak}, Lukas J. and {Glazebrook}, Karl and {Heintz}, Kasper E. and {Leja}, Joel and {Marchesini}, Danilo and {Nanayakkara}, Themiya and {Nelson}, Erica J. and {Oesch}, Pascal A. and {Pan}, Richard and {Price}, Sedona H. and {Shivaei}, Irene and {Sobral}, David and {Suess}, Katherine A. and {van Dokkum}, Pieter and {Wang}, Bingjie and {Weaver}, John R. and {Whitaker}, Katherine E. and {Zitrin}, Adi}, title = {{An unambiguous AGN and a Balmer break in an Ultraluminous Little Red Dot at z=4.47 from Ultradeep UNCOVER and All the Little Things Spectroscopy}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = dec, eid = {arXiv:2412.04557}, pages = {arXiv:2412.04557}, doi = {10.48550/arXiv.2412.04557}, archiveprefix = {arXiv}, eprint = {2412.04557}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241204557L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, emission lines, jwst, spectroscopy}, month_numeric = {12} }

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Halo mergers enhance the growth of massive black hole seeds

Lewis R. Prole, John A. Regan, Daniel J. Whalen, and 2 more authors

Astronomy & Astrophysics, Dec 2024

Abs DOI ADS arXiv

Context. High-redshift observations of 10^9 M_\ensuremath⊙ supermassive black holes (SMBHs) at z \ensuremath∼ 7 and ’little red dots’ that may host over- massive black holes (BHs) at z > 4 suggests the existence of so- called heavy seeds (> 1000 M_\ensuremath⊙) in the early Universe. Recent work has suggested that the rapid assembly of halos may be the key to forming heavy seeds early enough in the Universe to match such observations, as the high rate of accretion into the halo suppresses the cooling ability of H_2, allowing it to quickly accrete up to the atomic cooling limit of 10^7 M_\ensuremath⊙ prior to the run-away collapse of baryonic gas within its dark matter (DM) potential, without the need for extreme radiation fields or DM streaming velocities. Aims. While the rapid assembly of halos can lead to increased halo masses upon the onset of collapse, it remains unclear if this leads to higher-mass BH seeds. As a common route for halos to grow rapidly is via halo-halo mergers, we aim to test what effects such a merger occurring during the initial gas collapse has on the formation of BH seeds. Methods. We performed simulations of BH seed formation in four distinct idealised halo collapse scenarios: an isolated 10^6 M_\ensuremath⊙ minihalo, an isolated 10^7 M_\ensuremath⊙ atomic halo, the direct collision of two 10^7 M_\ensuremath⊙ halos, and a fly-by collision of two 10^7 M_\ensuremath⊙ halos. We simulated the collapse of the gas down to scales of \ensuremath∼0.0075 pc before inserting sink particles as BH seeds and captured a further 10 Myr of accretion. Results. We have shown that halo collisions create a central environment of increased density, inside which BH seeds can accrete at higher rates. For direct collisions, the gas density peaks are disrupted by the interaction, as the collisionless DM peaks pass through each other while the colliding gas is left in the centre, removing the BH from its accretion source. When the central density peaks instead experience a fly-by interaction, the BH remains embedded in the dense gas and maintains higher accretion rates throughout the simulated period compared to the isolated halo cases. The total simulated period was 70 Myr, and we followed the evolution of the BH for the final 10 Myr. The BH spends the final 6 Myr embedded in the dense, shocked region. The final mass of the BH is a factor of 2 greater than in the isolated atomic halo case, and a factor of 3 greater than the minihalo case, reaching 10^4 M_\ensuremath⊙ via its 0.03 pc accretion radius. As the maximum halo mass before collapse is determined by the atomic cooling limit of a few times 10^7 M_\ensuremath⊙, the ability of halo-halo mergers to further boost the rates of accretion onto the central object may play a crucial role in growing SMBH seeds, which is needed to explain recent observations of seemingly over-massive BHs at high redshifts.

@article{2024A&A...692A.213P, author = {{Prole}, Lewis R. and {Regan}, John A. and {Whalen}, Daniel J. and {Glover}, Simon C. O. and {Klessen}, Ralf S.}, title = {{Halo mergers enhance the growth of massive black hole seeds}}, journal = {\aap}, keywords = {stars: black holes, stars: luminosity function, mass function, stars: massive, stars: Population III, quasars: supermassive black holes, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2024}, month = dec, volume = {692}, eid = {A213}, pages = {A213}, doi = {10.1051/0004-6361/202452486}, archiveprefix = {arXiv}, eprint = {2410.06141}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024A\&A...692A.213P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, heavy seed, simulation, theory}, month_numeric = {12} }

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Discovery of dual “little red dots” indicates excess clustering on kilo-parsec scales

Takumi S. Tanaka, John D. Silverman, Kazuhiro Shimasaku, and 44 more authors

arXiv e-prints, Dec 2024

Abs DOI ADS arXiv

“Little Red Dots” (LRDs) are an abundant high-redshift population newly discovered by the James Webb Space Telescope (JWST). They are characterized by a red color in the rest-frame optical band, compact morphology, and broad Balmer emission lines (\rm FWHM rsim 1000~\rm km s^-1) that suggest an AGN nature. Using a method of pixel-by-pixel color selection and relaxing the compactness criteria, we identify three of the first dual LRD candidates in the COSMOS-Web survey with projected separations of 0.\!\!^\prime\prime2-0.\!\!^\prime\prime4 (1-2 pkpc at their photometric redshifts). A comparison between existing LRD samples and mock data reveals that the projected separations of these dual LRD candidates are unlikely to result from chance projections of objects at different redshifts. In one case (CW-B5-15958), the dual LRD includes two bright sources (m_\rm F444W=24.3 and 24.8) with characteristic V-shape spectral energy distribution (SEDs) and photometric redshifts consistent with each other. We find that CW-B5-15958 has a faint off- centered component and a companion galaxy. In the other two dual systems, the brighter LRD exhibits a V-shape SED, while the fainter LRD (m_\rm F444Wrsim26) is undetected in both F115W and F150W. These discoveries suggest that the angular auto- correlation function (ACF) of LRDs exhibits a significant excess (\sim3\times10^2 times) on sub-arcsec (kilo-parsec) separations compared to the extrapolation of a power-law ACF of JWST-found AGNs measured over 10^\prime\prime-100^\prime\prime. Follow-up spectroscopic confirmation of their redshifts and the construction of a larger sample are essential to advance our understanding of the evolution of supermassive black holes and the importance of mergers in the early universe.

@article{2024arXiv241214246T, author = {{Tanaka}, Takumi S. and {Silverman}, John D. and {Shimasaku}, Kazuhiro and {Arita}, Junya and {Akins}, Hollis B. and {Inayoshi}, Kohei and {Ding}, Xuheng and {Onoue}, Masafusa and {Liu}, Zhaoxuan and {Casey}, Caitlin M. and {Lambrides}, Erini and {Kokorev}, Vasily and {Jin}, Shuowen and {Faisst}, Andreas L. and {Drakos}, Nicole and {Shen}, Yue and {Li}, Junyao and {Zhuang}, Mingyang and {Fei}, Qinyue and {Ito}, Kei and {Ren}, Wenke and {Matsui}, Suin and {Ando}, Makoto and {Hatano}, Shun and {Fujii}, Michiko S. and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Liu}, Daizhong and {McCracken}, Henry Joy and {Rhodes}, Jason and {Robertson}, Brant E. and {Franco}, Maximilien and {Andika}, Irham T. and {Cloonan}, Aidan P. and {Fan}, Xiaohui and {Gozaliasl}, Ghassem and {Harish}, Santosh and {Hayward}, Christopher C. and {Huertas-Company}, Marc and {Kakkad}, Darshan and {Kinugawa}, Tomoya and {Roy}, Namrata and {Shuntov}, Marko and {Talia}, Margherita and {Toft}, Sune and {Vijayan}, Aswin P. and {Zhang}, Yiyang}, title = {{Discovery of dual ``little red dots'' indicates excess clustering on kilo-parsec scales}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = dec, eid = {arXiv:2412.14246}, pages = {arXiv:2412.14246}, doi = {10.48550/arXiv.2412.14246}, archiveprefix = {arXiv}, eprint = {2412.14246}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241214246T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, clustering, emission lines, jwst, sed}, month_numeric = {12} }

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Dust in Little Red Dots

Caitlin M. Casey, Hollis B. Akins, Vasily Kokorev, and 5 more authors

The Astrophysical Journal Letters, Nov 2024

Abs DOI ADS arXiv

JWST has revealed a ubiquitous population of “little red dots” (LRDs) at z \ensuremath≳ 4, selected via their red rest-frame optical emission and compact morphologies. They are thought to be reddened by dust, whether in tori of active galactic nuclei (AGNs) or the interstellar medium, though none have direct dust detections to date. Informed by the average characteristics of 675 LRDs drawn from the literature, we provide ballpark constraints on the dust characteristics of the LRD population and estimate they have average dust masses of Mdust>=(1.6‑0.9+4.8)\texttimes104 M _\ensuremath⊙, luminosities of LIR>=(8‑5+3)\texttimes1010 L _\ensuremath⊙, and temperatures of Tdust>=110‑36+21 K. Notably, the spectral energy distributions are thought to peak at \ensuremath∼100 K (rest-frame 20–30 \ensuremathμm) regardless of heating mechanism, whether AGN or star formation. LRDs’ compact sizes R _eff \ensuremath∼ 100 pc are the dominant factor contributing to their low estimated dust masses. Our predictions likely mean LRDs have, on average, a submillimeter emission factor of \ensuremath∼100\texttimes fainter than current Atacama Large Millimeter/submillimeter Array limits provide. The star- to-dust ratio is a factor \ensuremath∼100\texttimes larger than expected from dust formation models if one assumes the rest-optical light is dominated by stars; this suggests stars do not dominate. Despite their high apparent volume density, LRDs contribute negligibly (0.1%) to the cosmic dust budget at z \ensuremath≳ 4 due to their low dust masses.

@article{2024ApJ...975L...4C, author = {{Casey}, Caitlin M. and {Akins}, Hollis B. and {Kokorev}, Vasily and {McKinney}, Jed and {Cooper}, Olivia R. and {Long}, Arianna S. and {Franco}, Maximilien and {Manning}, Sinclaire M.}, title = {{Dust in Little Red Dots}}, journal = {\apjl}, keywords = {AGN host galaxies, Dust continuum emission, James Webb Space Telescope, 2017, 412, 2291, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = nov, volume = {975}, number = {1}, eid = {L4}, pages = {L4}, doi = {10.3847/2041-8213/ad7ba7}, archiveprefix = {arXiv}, eprint = {2407.05094}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...975L...4C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, jwst, morphology, sed}, month_numeric = {11} }

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Consistency of JWST black hole observations with NANOGrav gravitational wave measurements

John Ellis, Malcolm Fairbairn, Gert Hütsi, and 3 more authors

Astronomy & Astrophysics, Nov 2024

Abs DOI ADS arXiv

JWST observations have opened a new chapter in supermassive black hole (SMBH) studies, stimulating discussion of two puzzles: the abundance of high-z SMBHs and the fraction of dual active galactic nuclei (AGNs). We argue that the answers to these puzzles may be linked to an interpretation of the data on the nanohertz gravitational waves (GWs) discovered by NANOGrav and other pulsar timing arrays as SMBH binaries whose evolution is driven by interactions with their environments down to O(0.1 pc) separations. We show that the stellar mass-black hole mass correlations found in JWST data and in low-ɀ inactive galaxies are similar, and present a global fit to these data, excluding low-ɀ AGNs. Matching the NANOGrav and dual-AGN data requires that binary evolution due to environmental effects at separations below O(1 kpc) be rapid on cosmological timescales. According to this interpretation, the SMBHs in low-ɀ AGNs are the tip of the iceberg of a local SMBH population in mainly inactive galaxies. This interpretation is consistent with the ’little red dots’ observed with JWST being AGNs, and would favour the observability of GW signals from black hole binaries in LISA and decihertz GW detectors.

@article{2024A&A...691A.270E, author = {{Ellis}, John and {Fairbairn}, Malcolm and {H{\"u}tsi}, Gert and {Urrutia}, Juan and {Vaskonen}, Ville and {Veerm{\"a}e}, Hardi}, title = {{Consistency of JWST black hole observations with NANOGrav gravitational wave measurements}}, journal = {\aap}, keywords = {quasars: supermassive black holes, cosmology: theory, early Universe, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology}, year = {2024}, month = nov, volume = {691}, eid = {A270}, pages = {A270}, doi = {10.1051/0004-6361/202450846}, archiveprefix = {arXiv}, eprint = {2403.19650}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024A\&A...691A.270E}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, jwst, theory}, month_numeric = {11} }

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Deciphering the JWST spectrum of a ’little red dot’ at z \ensuremath∼ 4.53: An obscured AGN and its star-forming host

Meghana Killi, Darach Watson, Gabriel Brammer, and 10 more authors

Astronomy & Astrophysics, Nov 2024

Abs DOI ADS arXiv

JWST has revealed a class of numerous, extremely compact sources with rest-frame red optical/near-infrared (NIR) and blue ultraviolet (UV) colours nicknamed ’little red dots’. We present one of the highest signal-to-noise ratio JWST NIRSpec prism spectra of a little red dot, J0647_1045 at z = 4.5319 \ensuremath\pm 0.0001, and examine its NIRCam morphology to differentiate the origin of the UV and optical/NIR emission and elucidate the nature of the little red dot phenomenon. J0647_1045 is unresolved (r_e \ensuremath≲ 0.17 kpc) in the three NIRCam long-wavelength filters but significantly extended (r_e = 0.45 \ensuremath\pm 0.06 kpc) in the three short- wavelength filters, indicating a red compact source in a blue star-forming galaxy. The spectral continuum shows a clear change in slope, from blue in the optical/UV to red in the rest-frame optical/NIR, which is consistent with two distinct components fit by power laws with different attenuations: A_V = 0.38 \ensuremath\pm 0.01 (UV) and A_V = 5.61 \ensuremath\pm 0.04 (optical/NIR). Fitting the H\ensuremathα line requires both broad (full width at half maximum of \ensuremath∼4300 \ensuremath\pm 100 km s^‑1) and narrow components, but none of the other emission lines, including H\ensuremathβ, show evidence of broadness. We calculated A_V = 0.9 \ensuremath\pm 0.4 from the Balmer decrement using narrow H\ensuremathα and H\ensuremathβ and A_V > 4.1 \ensuremath\pm 0.1 from broad H\ensuremathα and an upper limit on broad H\ensuremathβ, which is consistent with blue and red continuum attenuation, respectively. Based on a single-epoch H\ensuremathα line width, the mass of the central black hole is 8_‑0.4^+0.5 \texttimes 10^8 M_\ensuremath⊙. Our findings are consistent with a multi-component model, in which the optical/NIR and broad lines arise from a highly obscured, spatially unresolved region, likely a relatively massive active galactic nucleus, while the less obscured UV continuum and narrow lines arise, at least partly, from a small but spatially resolved star-forming host galaxy.

@article{2024A&A...691A..52K, author = {{Killi}, Meghana and {Watson}, Darach and {Brammer}, Gabriel and {McPartland}, Conor and {Antwi-Danso}, Jacqueline and {Newshore}, Rosa and {Coe}, Dan and {Allen}, Natalie and {Fynbo}, Johan P. U. and {Gould}, Katriona and {Heintz}, Kasper E. and {Rusakov}, Vadim and {Vejlgaard}, Simone}, title = {{Deciphering the JWST spectrum of a 'little red dot' at z {\ensuremath{\sim}} 4.53: An obscured AGN and its star-forming host}}, journal = {\aap}, keywords = {galaxies: active, galaxies: evolution, galaxies: high-redshift, quasars: emission lines, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = nov, volume = {691}, eid = {A52}, pages = {A52}, doi = {10.1051/0004-6361/202348857}, archiveprefix = {arXiv}, eprint = {2312.03065}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024A\&A...691A..52K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, jwst, morphology, obscuration, spectroscopy}, month_numeric = {11} }

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Silencing the Giant: Evidence of Active Galactic Nucleus Feedback and Quenching in a Little Red Dot at z = 4.13

Vasily Kokorev, John Chisholm, Ryan Endsley, and 8 more authors

The Astrophysical Journal, Nov 2024

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has uncovered a ubiquitous population of dust-obscured compact sources at z \ensuremath≳ 4. Many of these objects exhibit signs of active galactic nucleus (AGN) activity, making their study crucial for understanding the formation of supermassive black holes (SMBHs) and their growth with host galaxies. In this work, we examine low and medium-resolution JWST/NIRSpec spectra from the JADES GTO public data release in the GOODS-N field of a red, luminous (M _B \ensuremath∼ ‑22.2 mag) and compact ( 4000 Å) continuum of this source is strongly dominated by a massive (log_10[M _*/M _\ensuremath⊙] \ensuremath∼ 10.6), quenched (log_10[sSFR/yr^‑1] < ‑11) galaxy, as indicated by the clear presence of a Balmer break and stellar absorption lines. Star formation history modeling reveals a starburst episode followed by rapid quenching about 200 Myr ago. The spectrum shows extremely broad (FWHM \ensuremath∼2500 km s^‑1) H\ensuremathα emission and elevated optical line ratios, indicating an actively accreting SMBH. Moreover, our work has potentially revealed clear AGN signatures in the rest-UV in little red dots for the first time via the detection of a strong Ly\ensuremathα emission and a broad Mg II doublet. The derived black hole mass of log_10(M _BH/M _\ensuremath⊙) \ensuremath∼ 7.3 results in M _BH/M _* \ensuremath∼ 0.04%, consistent with the local relations, unlike the elevated ratios in other high-z reddened AGN. Finally, we use JWST data from AGN at z = 4–10 to explore an evolutionary link between high-z reddened AGN, early quiescent galaxies, and local ellipticals.

@article{2024ApJ...975..178K, author = {{Kokorev}, Vasily and {Chisholm}, John and {Endsley}, Ryan and {Finkelstein}, Steven L. and {Greene}, Jenny E. and {Akins}, Hollis B. and {Bromm}, Volker and {Casey}, Caitlin M. and {Fujimoto}, Seiji and {Labb{\'e}}, Ivo and {Larson}, Rebecca L.}, title = {{Silencing the Giant: Evidence of Active Galactic Nucleus Feedback and Quenching in a Little Red Dot at z = 4.13}}, journal = {\apj}, keywords = {Active galactic nuclei, High-redshift galaxies, Early universe, Galaxy quenching, Quenched galaxies, 16, 734, 435, 2040, 2016, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = nov, volume = {975}, number = {2}, eid = {178}, pages = {178}, doi = {10.3847/1538-4357/ad7d03}, archiveprefix = {arXiv}, eprint = {2407.20320}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...975..178K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, early universe, jwst, spectroscopy}, month_numeric = {11} }

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Probing the Origin of the Star Formation Excess Discovered by JWST through Gamma-Ray Bursts

Tatsuya Matsumoto, Yuichi Harikane, Keiichi Maeda, and 1 more author

The Astrophysical Journal Letters, Nov 2024

Abs DOI ADS arXiv

The recent observations by the James Webb Space Telescope (JWST) have revealed a larger number of bright galaxies at z \ensuremath≳ 10 than was expected. The origin of this excess is still under debate, although several possibilities have been presented. We propose that gamma-ray bursts (GRBs) are a powerful probe to explore the origin of the excess and, hence, the star and galaxy formation histories in the early universe. Focusing on the recently launched mission, Einstein Probe (EP), we find that EP can detect several GRBs annually at z \ensuremath≳ 10, assuming the GRB formation rate calibrated by events at z \ensuremath≲ 6 can be extrapolated. Interestingly, depending on the excess scenarios, the GRB event rate may also show an excess at z ≃ 10, and its detection will help to discriminate between the scenarios that are otherwise difficult to distinguish. Additionally, we discuss that the puzzling, red-color, compact galaxies discovered by JWST, the so-called “little red dots,” could host dark GRBs if they are dust-obscured star-forming galaxies. We are eager for unbiased follow-up of GRBs and encourage future missions such as HiZ-GUNDAM to explore the early universe.

@article{2024ApJ...976L..16M, author = {{Matsumoto}, Tatsuya and {Harikane}, Yuichi and {Maeda}, Keiichi and {Ioka}, Kunihito}, title = {{Probing the Origin of the Star Formation Excess Discovered by JWST through Gamma-Ray Bursts}}, journal = {\apjl}, keywords = {Gamma-ray bursts, 629, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = nov, volume = {976}, number = {1}, eid = {L16}, pages = {L16}, doi = {10.3847/2041-8213/ad8ce0}, archiveprefix = {arXiv}, eprint = {2409.11468}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...976L..16M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, jwst, starburst}, month_numeric = {11} }

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Mildly Super-Eddington Accretion onto Slowly Spinning Black Holes Explains the X-Ray Weakness of the Little Red Dots

Fabio Pacucci and Ramesh Narayan

The Astrophysical Journal, Nov 2024

Abs DOI ADS arXiv

JWST has revealed a population of low-luminosity active galactic nuclei at z > 4 in compact, red hosts (the “Little Red Dots,” or LRDs), which are largely undetected in X-rays. We investigate this phenomenon using General Relativistic Radiation Magnetohydrodynamics simulations of super-Eddington accretion onto a supermassive black hole (SMBH) with M _• = 10^7 M _\ensuremath⊙ at z \ensuremath∼ 6, representing the median population; the spectral energy distributions (SEDs) that we obtain are intrinsically X-ray weak. The highest levels of X-ray weakness occur in SMBHs accreting at mildly super-Eddington rates (1.4 30\textdegree from the pole. X-ray bolometric corrections in the observed 2–10 keV band reach \ensuremath∼10^4 at z = 6, \ensuremath∼5 times higher than the highest constraint from X-ray stacking. Most SEDs are extraordinarily steep and soft in the X-rays (median photon index \ensuremathΓ = 3.1, mode of \ensuremathΓ = 4.4). SEDs strong in the X-rays have harder spectra with a high-energy bump when viewed near the hot (>10^8 K) and highly relativistic jet, whereas X-ray weak SEDs lack this feature. Viewing an SMBH within 10\textdegree of its pole, where beaming enhances the X-ray emission, has a \ensuremath∼1.5% probability, matching the LRD X-ray detection rate. Next-generation observatories like AXIS will detect X-ray-weak LRDs at z \ensuremath∼ 6 from any viewing angle. Although many SMBHs in the LRDs are already estimated to accrete at super-Eddington rates, our model explains 50% of their population by requiring that their masses are overestimated by a mere factor of \ensuremath∼3. In summary, we suggest that LRDs host slowly spinning SMBHs accreting at mildly super-Eddington rates, with large covering factors and broad emission lines enhanced by strong winds, providing a self-consistent explanation for their X-ray weakness and complementing other models.

@article{2024ApJ...976...96P, author = {{Pacucci}, Fabio and {Narayan}, Ramesh}, title = {{Mildly Super-Eddington Accretion onto Slowly Spinning Black Holes Explains the X-Ray Weakness of the Little Red Dots}}, journal = {\apj}, keywords = {Active galaxies, Supermassive black holes, Black holes, Accretion, Spectral energy distribution, 17, 1663, 162, 14, 2129, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = nov, volume = {976}, number = {1}, eid = {96}, pages = {96}, doi = {10.3847/1538-4357/ad84f7}, archiveprefix = {arXiv}, eprint = {2407.15915}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...976...96P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, sed, simulation, super-eddington, x-ray}, month_numeric = {11} }

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Sub-Eddington accreting supermassive primordial black holes explain Little Red Dots

Hai-Long Huang, Jun-Qian Jiang, Jibin He, and 2 more authors

arXiv e-prints, Oct 2024

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has uncovered an abundant population of compact, extremely red, and X-ray weak objects at zrsim4, knows as “Little Red Dots” (LRDs). These objects exhibit spectral energy distributions that resemble both active galactic nuclei (AGN) and stellar population templates. However, whether dominated by AGN activity or compact star formation, the high redshifts and masses/luminosities of LRDs, coupled with their significant abundance, present potential challenges to the standard \LambdaCDM model. In this work, we proposes a novel cosmic interpretation of this anomaly, suggesting that these LRDs are likely massive galaxies seeded by supermassive primordial black holes (SMPBHs) came into being in the very early universe. We analyze 434 known LRDs from the 0.54 \rm deg^2 COSMOS-Web survey and test the hypothesis that they originated from SMPBHs assuming sub-Eddington accretion. According to our result, SMPBHs actually could lead to the existence of more LRDs, even at higher redshifts (z>8).

@article{2024arXiv241020663H, author = {{Huang}, Hai-Long and {Jiang}, Jun-Qian and {He}, Jibin and {Wang}, Yu-Tong and {Piao}, Yun-Song}, title = {{Sub-Eddington accreting supermassive primordial black holes explain Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2024}, month = oct, eid = {arXiv:2410.20663}, pages = {arXiv:2410.20663}, doi = {10.48550/arXiv.2410.20663}, archiveprefix = {arXiv}, eprint = {2410.20663}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241020663H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, theory}, month_numeric = {10} }

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Birth of Rapidly Spinning, Overmassive Black Holes in the Early Universe

Kohei Inayoshi and Kohei Ichikawa

The Astrophysical Journal Letters, Oct 2024

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has unveiled numerous massive black holes (BHs) in faint, broad-line active galactic nuclei (AGNs). The discovery highlights the presence of dust-reddened AGN populations, referred to as “little red dots (LRDs),” more abundant than X-ray-selected AGNs, which are less influenced by obscuration. This finding indicates that the cosmic growth rate of BHs within this population does not decrease but rather increases at higher redshifts beyond z \ensuremath∼ 6. The BH accretion rate density deduced from their luminosity function is remarkably higher than that from other AGN surveys in X-ray and infrared bands. To align the cumulative mass density accreted to BHs with the observed BH mass density at z ≃ 4–5, as derived from the integration of the BH mass function, the radiative efficiency must be doubled from the canonical 10% value, achieving significance beyond the >3\ensuremathσ confidence level. This suggests the presence of rapid spins with 96% of the maximum limit among these BHs under the thin-disk approximation, maintained by prolonged mass accretion instead of chaotic accretion with randomly oriented inflows. Moreover, we derive an upper bound for the stellar mass of galaxies hosting these LRDs, ensuring consistency with galaxy formation in the standard cosmological model, where the host stellar mass is limited by the available baryonic reservoir. Our analysis gives a lower bound for the BH- to-galaxy mass ratio that exceeds the typical value known in the nearby universe and aligns with that for JWST-detected unobscured AGNs. Accordingly, we propose a hypothesis that the dense, dust-rich environments within LRDs facilitate the emergence of rapidly spinning and overmassive BH populations during the epoch of reionization. This scenario predicts a potential association between relativistic jets and other high- energy phenomena with overmassive BHs in the early universe.

@article{2024ApJ...973L..49I, author = {{Inayoshi}, Kohei and {Ichikawa}, Kohei}, title = {{Birth of Rapidly Spinning, Overmassive Black Holes in the Early Universe}}, journal = {\apjl}, keywords = {Galaxy formation, High-redshift galaxies, Quasars, Supermassive black holes, 595, 734, 1319, 1663, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = oct, volume = {973}, number = {2}, eid = {L49}, pages = {L49}, doi = {10.3847/2041-8213/ad74e2}, archiveprefix = {arXiv}, eprint = {2402.14706}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...973L..49I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, black hole mass, dust-reddened, early universe, jwst}, month_numeric = {10} }

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JWST’s Little Red Dots

Marc Pfeiffer

\skytel, Oct 2024

ADS

@article{2024S&T...148d...7P, author = {{Pfeiffer}, Marc}, title = {{JWST's Little Red Dots}}, journal = {\skytel}, year = {2024}, month = oct, volume = {148}, number = {4}, pages = {7}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024S\&T...148d...7P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {catalog, jwst, multi-wavelength, photometry, sed}, month_numeric = {10} }

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Stacking X-Ray Observations of “Little Red Dots”: Implications for Their Active Galactic Nucleus Properties

Minghao Yue, Anna-Christina Eilers, Tonima Tasnim Ananna, and 3 more authors

The Astrophysical Journal Letters, Oct 2024

Abs DOI ADS arXiv

Recent James Webb Space Telescope observations have revealed a population of compact extragalactic objects at z \ensuremath≳ 4 with red near-infrared colors, which have been dubbed as “Little Red Dots” (LRDs). The spectroscopically selected LRDs exhibit broad H\ensuremathα emission lines, which likely indicate that type I active galactic nuclei (AGNs) are harbored in the galaxies’ dust-reddened cores. However, other mechanisms, like strong outflowing winds, could also produce broad H\ensuremathα emission lines, and thus, the nature of LRDs is still under debate. We test the AGN hypothesis for LRDs by stacking the archival Chandra observations of 34 spectroscopically selected LRDs. We obtain tentative detections in the soft (0.5─2 keV) and hard (2─8 keV) X-ray bands with 2.9\ensuremathσ and 3.2\ensuremathσ significance, and with 4.1\ensuremathσ significance when combining the two bands. Nevertheless, we find that the soft (hard) band 3\ensuremathσ upper limit is \ensuremath∼1 dex (\ensuremath∼0.3 dex) lower than the expected level from the L _X─L _H\ensuremathα relation for typical type I AGNs. Our results indicate that AGN activity is indeed likely present in LRDs though these objects have significantly different properties compared to previously identified type I AGNs, i.e., LRDs may have intrinsically weak X-ray emissions. We find it difficult to explain the low L _X/L _H\ensuremathα ratios observed in LRDs solely by absorption. It is also unlikely that fast outflows have major contributions to the broad H\ensuremathα lines. Our findings indicate that empirical relations (e.g., for black hole mass measurements) established for typical type I AGNs should be used with caution when analyzing the properties of LRDs.

@article{2024ApJ...974L..26Y, author = {{Yue}, Minghao and {Eilers}, Anna-Christina and {Ananna}, Tonima Tasnim and {Panagiotou}, Christos and {Kara}, Erin and {Miyaji}, Takamitsu}, title = {{Stacking X-Ray Observations of ``Little Red Dots'': Implications for Their Active Galactic Nucleus Properties}}, journal = {\apjl}, keywords = {Active galactic nuclei, 16, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = oct, volume = {974}, number = {2}, eid = {L26}, pages = {L26}, doi = {10.3847/2041-8213/ad7eba}, archiveprefix = {arXiv}, eprint = {2404.13290}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...974L..26Y}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, early universe, obscuration, spectroscopy, x-ray}, month_numeric = {10} }

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Searching For JWST’s Little Red Dots

Jake Feeney, Patrick Kavanagh, and John A. Regan

arXiv e-prints, Sep 2024

Abs DOI ADS arXiv

Recent observations by the James Webb Space Telescope (JWST) have revealed a previously hidden population of extremely bright and compact objects between redshifts of z ∼4 and z ∼10. Given their extreme red colouring in the observed frame these galaxies have been dubbed Little Red Dots (LRDs). The aim of this project was to identify LRDs using photometric data from previously uninvestigated JWST datasets and to estimate their AGN fractions by fitting the spectral energy distribution of each galaxy against well calibrated templates using CIGALE. We identified a list of potential LRDs using a single colour cut of F444W-F277W >1.5 mag and by applying a morphological analysis. We used EAZY to estimate the (photometric) redshift and CIGALE to estimate the AGN fraction of each LRD. Overall, we identified 14 LRDs, applying accurate SED fits to 11 of them. We found that 7 of them had a high AGN fraction (with the AGN component generating more than 50\% of the observed flux), a further two LRDs had AGN contribution in excess of approximately 40\%. In total nine LRDs (our of 14) are likely to have a supermassive black hole in their centre. Interestingly, the three LRDs which could not be well fit by CIGALE displayed extremely high photometric redshifts (z_phot rsim 11) and require further analysis (and may also host a supermassive black hole in their centre).

@article{2024arXiv240913441F, author = {{Feeney}, Jake and {Kavanagh}, Patrick and {Regan}, John A.}, title = {{Searching For JWST's Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = sep, eid = {arXiv:2409.13441}, pages = {arXiv:2409.13441}, doi = {10.48550/arXiv.2409.13441}, archiveprefix = {arXiv}, eprint = {2409.13441}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv240913441F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, early universe, jwst, photometry, sed}, month_numeric = {9} }

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Not-so-little Red Dots: Two Massive and Dusty Starbursts at z \ensuremath∼ 5–7 Pushing the Limits of Star Formation Discovered by JWST in the COSMOS-Web Survey

Fabrizio Gentile, Caitlin M. Casey, Hollis B. Akins, and 24 more authors

The Astrophysical Journal Letters, Sep 2024

Abs DOI ADS arXiv

We present the properties of two candidate massive (M _\ensuremath⋆ \ensuremath∼ 10^11 M _\ensuremath⊙) and dusty (A _v > 2.5 mag) galaxies at z = 5–7 in the first 0.28 deg^2 of the COSMOS-Web survey. One object is spectroscopically confirmed at z _spec = 5.051, while the other has a robust z _phot = 6.7 \ensuremath\pm 0.3. Thanks to their extremely red colors (F277W–F444W \ensuremath∼ 1.7 mag), these galaxies satisfy the nominal color selection for the widely studied “little red dot” (LRD) population with the exception of their spatially resolved morphologies. The morphology of our targets allows us to conclude that their red continuum is dominated by highly obscured stellar emission and not by reddened nuclear activity. Using a variety of spectral energy distribution fitting tools and star formation histories, we estimate the stellar masses to be log(M\ensuremath⋆)=11.32‑0.15+0.07M\ensuremath⊙ and log(M\ensuremath⋆)=11.2‑0.2+0.1M\ensuremath⊙, respectively, with a red continuum emission dominated by a recent episode of star formation. We then compare their number density to the halo mass function to infer stellar baryon fractions of ϵ _\ensuremath⋆ \ensuremath∼ 0.25 and ϵ _\ensuremath⋆ \ensuremath∼ 0.5. Both are significantly higher than what is commonly observed in lower-z galaxies or more dust-obscured galaxies at similar redshifts. With very bright ultra-high-z Lyman-Break Galaxies and some non-AGN-dominated LRDs, such “extended” LRDs represent another population that may require very efficient star formation at early times.

@article{2024ApJ...973L...2G, author = {{Gentile}, Fabrizio and {Casey}, Caitlin M. and {Akins}, Hollis B. and {Franco}, Maximilien and {McKinney}, Jed and {Berman}, Edward and {Cooper}, Olivia R. and {Drakos}, Nicole E. and {Hirschmann}, Michaela and {Long}, Arianna S. and {Magdis}, Georgios and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Shuntov}, Marko and {Talia}, Margherita and {Allen}, Natalie and {Harish}, Santosh and {Ilbert}, Olivier and {McCracken}, Henry Joy and {Kartaltepe}, Jeyhan S. and {Liu}, Daizhong and {Paquereau}, Louise and {Rhodes}, Jason and {Rich}, Michael R. and {Robertson}, Brant E. and {Toft}, Sune and {Gozaliasl}, Ghassem}, title = {{Not-so-little Red Dots: Two Massive and Dusty Starbursts at z {\ensuremath{\sim}} 5{\textendash}7 Pushing the Limits of Star Formation Discovered by JWST in the COSMOS-Web Survey}}, journal = {\apjl}, keywords = {Galaxy evolution, Galaxy formation, High-redshift galaxies, Star formation, Galaxies, 594, 595, 734, 1569, 573, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2024}, month = sep, volume = {973}, number = {1}, eid = {L2}, pages = {L2}, doi = {10.3847/2041-8213/ad738a}, archiveprefix = {arXiv}, eprint = {2408.10305}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...973L...2G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, jwst, sed, starburst}, month_numeric = {9} }

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Tiny, compact galaxies are masters of disguise in the distant universe

Fabio Pacucci

The Conversation, Sep 2024

Abs ADS

Article for The Conversation describing the latest findings regarding JWST’s Little Red Dots: a population of high-redshift, compact galaxies with remarkable observational properties.

@article{2024Conve2024....1P, author = {{Pacucci}, Fabio}, title = {{Tiny, compact galaxies are masters of disguise in the distant universe}}, journal = {The Conversation}, year = {2024}, month = sep, volume = {2024}, pages = {1-2}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024Conve2024....1P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, jwst, starburst}, month_numeric = {9} }

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A big red dot: scattered light, host galaxy signatures, and multiphase gas flows in a luminous, heavily reddened quasar at cosmic noon

Matthew Stepney, Manda Banerji, Shenli Tang, and 5 more authors

Monthly Notices of the Royal Astronomical Society, Sep 2024

Abs DOI ADS arXiv

We present a deep X-Shooter rest-frame ultraviolet (UV) to optical spectral analysis of the heavily reddened quasar, ULASJ2315+0143 at , known to reside in a major-merger host galaxy. The rest- frame optical is best fit by a dust-reddened quasar (E(B - V)) with black-hole mass , bolometric luminosity = and Eddington- scaled accretion rate log. We find remarkable similarities between ULASJ2315+0143 and the high-redshift little red dots (LRDs). The rest-frame UV cannot be explained by a dusty quasar component alone and requires an additional blue component consistent with either a star-forming host galaxy or scattered AGN light. We detect broad high-ionization emission lines in the rest-UV, supporting the scattered light interpretation for the UV excess. The scattering fraction represents just 0.05 per cent of the total luminosity of ULASJ2315+0143 . Analysis of the mid- infrared SED suggests an absence of hot dust on torus-scales similar to what is observed for LRDs. The obscuring medium is therefore likely on galaxy scales. We detect narrow, blueshifted associated absorption-line systems in C IV, N V, Si IV, and Si III. There is evidence for significant high-velocity (>1000 ) outflows in both the broad- and narrow-line regions as traced by C IV and [O III] emission. The kinetic power of the [O III] wind is . ULASJ2315+0143 is likely in an important transition phase where star formation, black-hole accretion and multiphase gas flows are simultaneously occurring.

@article{2024MNRAS.533.2948S, author = {{Stepney}, Matthew and {Banerji}, Manda and {Tang}, Shenli and {Hewett}, Paul C. and {Temple}, Matthew J. and {Wethers}, Clare F. and {Puglisi}, Annagrazia and {Molyneux}, Stephen J.}, title = {{A big red dot: scattered light, host galaxy signatures, and multiphase gas flows in a luminous, heavily reddened quasar at cosmic noon}}, journal = {\mnras}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = sep, volume = {533}, number = {3}, pages = {2948-2965}, doi = {10.1093/mnras/stae1970}, archiveprefix = {arXiv}, eprint = {2408.10403}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024MNRAS.533.2948S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {absorption features, dust-reddened, emission lines, kinematics, spectroscopy}, month_numeric = {9} }

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Interpreting Multi-band Galaxy Observations with Large Language Model-Based Agents

Zechang Sun, Yuan-Sen Ting, Yaobo Liang, and 3 more authors

arXiv e-prints, Sep 2024

Abs DOI ADS arXiv

Astronomical research traditionally relies on extensive domain knowledge to interpret observations and narrow down hypotheses. We demonstrate that this process can be emulated using large language model-based agents to accelerate research workflows. We propose mephisto, a multi-agent collaboration framework that mimics human reasoning to interpret multi-band galaxy observations. mephisto interacts with the CIGALE codebase, which includes spectral energy distribution (SED) models to explain observations. In this open-world setting, mephisto learns from its self-play experience, performs tree search, and accumulates knowledge in a dynamically updated base. As a proof of concept, we apply mephisto to the latest data from the James Webb Space Telescope. mephisto attains near-human proficiency in reasoning about galaxies’ physical scenarios, even when dealing with a recently discovered population of “Little Red Dot” galaxies. This represents the first demonstration of agentic research in astronomy, advancing towards end-to-end research via LLM agents and potentially expediting astronomical discoveries.

@article{2024arXiv240914807S, author = {{Sun}, Zechang and {Ting}, Yuan-Sen and {Liang}, Yaobo and {Duan}, Nan and {Huang}, Song and {Cai}, Zheng}, title = {{Interpreting Multi-band Galaxy Observations with Large Language Model-Based Agents}}, journal = {arXiv e-prints}, keywords = {Instrumentation and Methods for Astrophysics, Astrophysics of Galaxies}, year = {2024}, month = sep, eid = {arXiv:2409.14807}, pages = {arXiv:2409.14807}, doi = {10.48550/arXiv.2409.14807}, archiveprefix = {arXiv}, eprint = {2409.14807}, primaryclass = {astro-ph.IM}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv240914807S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, multi-wavelength, non-agn, sed}, month_numeric = {9} }

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Sizes and Stellar Masses of the Little Red Dots Imply Immense Stellar Densities

Carl Audric Guia, Fabio Pacucci, and Dale D. Kocevski

Research Notes of the American Astronomical Society, Aug 2024

Abs DOI ADS arXiv

The “Little Red Dots” (LRDs) are red and compact galaxies detected in JWST deep fields, mainly in the redshift range z = 4–8. Given their compactness and the inferred stellar masses in the hypothesis that LRDs are starburst galaxies, the implied stellar densities are immense. This Research Note uses an extensive catalog of LRDs from the PRIMER and the COSMOS-Web surveys to investigate these densities. We find a median (upper limit) on the effective radius of 80 pc, which leads to median (lower limit) values of the core density of \ensuremath∼10^4 M _\ensuremath⊙ pc^‑3, and individual densities as high as \ensuremath∼10^8 M _\ensuremath⊙ pc^‑3, which is \ensuremath∼10 times higher than the density necessary for runaway collisions to take place. For \ensuremath∼35% of the LRDs investigated, the lower limits are higher than the highest stellar densities observed in any system in any redshift range.

@article{2024RNAAS...8..207G, author = {{Guia}, Carl Audric and {Pacucci}, Fabio and {Kocevski}, Dale D.}, title = {{Sizes and Stellar Masses of the Little Red Dots Imply Immense Stellar Densities}}, journal = {Research Notes of the American Astronomical Society}, keywords = {Galaxy evolution, Early universe, Surveys, Galaxies, 594, 435, 1671, 573, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena}, year = {2024}, month = aug, volume = {8}, number = {8}, eid = {207}, pages = {207}, doi = {10.3847/2515-5172/ad7262}, archiveprefix = {arXiv}, eprint = {2408.11890}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024RNAAS...8..207G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {catalog, early universe, jwst, morphology, starburst}, month_numeric = {8} }

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X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?

Tonima Tasnim Ananna, Ákos Bogdán, Orsolya E. Kovács, and 2 more authors

The Astrophysical Journal Letters, Jul 2024

Abs DOI ADS arXiv

The discovery of Little Red Dots (LRDs)—a population of compact, high-redshift, dust-reddened galaxies—is one of the most surprising results from JWST. However, the nature of LRDs is still debated: does the near-infrared emission originate from accreting supermassive black holes (SMBHs), or intense star formation? In this work, we utilize ultra-deep Chandra observations and study LRDs residing behind the lensing galaxy cluster, A2744. We probe the X-ray emission from individual galaxies but find that they remain undetected and provide SMBH mass upper limits of \ensuremath≲(1.5–16) \texttimes 10^6 M _\ensuremath⊙ assuming Eddington limited accretion. To increase the signal-to-noise ratios, we conduct a stacking analysis of the full sample with a total lensed exposure time of \ensuremath≈87 Ms. We also bin the galaxies based on their stellar mass, lensing magnification, and detected broad-line H\ensuremathα emission. For the LRDs exhibiting broad-line H\ensuremathα emission, there is a hint of a stacked signal (\ensuremath∼2.6\ensuremathσ), corresponding to an SMBH mass of \ensuremath∼3.2 \texttimes 10^6 M _\ensuremath⊙. Assuming unobscured, Eddington- limited accretion, this black hole (BH) mass is at least 1.5 orders of magnitude lower than that inferred from virial mass estimates using JWST spectra. Given galaxy-dominated stellar mass estimates, our results imply that LRDs do not host overmassive SMBHs and/or accrete at a few percent of their Eddington limit. However, alternative stellar mass estimates may still support that LRDs host overmassive BHs. The significant discrepancy between the JWST and Chandra data hints that the scaling relations used to infer the SMBH mass from the H\ensuremathα line and virial relations may not be applicable for high-redshift LRDs.

@article{2024ApJ...969L..18A, author = {{Ananna}, Tonima Tasnim and {Bogd{\'a}n}, {\'A}kos and {Kov{\'a}cs}, Orsolya E. and {Natarajan}, Priyamvada and {Hickox}, Ryan C.}, title = {{X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?}}, journal = {\apjl}, keywords = {Active galactic nuclei, James Webb Space Telescope, X-ray active galactic nuclei, Supermassive black holes, 16, 2291, 2035, 1663, Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena}, year = {2024}, month = jul, volume = {969}, number = {1}, eid = {L18}, pages = {L18}, doi = {10.3847/2041-8213/ad5669}, archiveprefix = {arXiv}, eprint = {2404.19010}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...969L..18A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, jwst, non-agn, starburst, x-ray}, month_numeric = {7} }

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Little Red Dots from Low-spin Galaxies at High Redshifts

Abraham Loeb

Research Notes of the American Astronomical Society, Jul 2024

Abs DOI ADS arXiv

Recently, a new population of compact, high-redshift (z \ensuremath≳ 7) galaxies appeared as little red dots (LRDs) in deep JWST observations. The latest spectroscopic data indicates that these galaxies contain an evolved stellar population, reflecting an early episode of high star formation- rate. The appearance of broad emission lines suggests that a central overmassive black hole also powers these galaxies. I propose that LRD galaxies represent the low-spin tail of the galaxy population. Low-spin galaxies host a more compact gaseous disk with an enhanced star formation rate relative to typical galaxies at the same redshift. The compact disk feeds efficiently a central black hole, as predicted by Eisenstein & Loeb.

@article{2024RNAAS...8..182L, author = {{Loeb}, Abraham}, title = {{Little Red Dots from Low-spin Galaxies at High Redshifts}}, journal = {Research Notes of the American Astronomical Society}, keywords = {Compact galaxies, AGN host galaxies, 285, 2017, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2024}, month = jul, volume = {8}, number = {7}, eid = {182}, pages = {182}, doi = {10.3847/2515-5172/ad614c}, archiveprefix = {arXiv}, eprint = {2407.12965}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024RNAAS...8..182L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, heavy seed, jwst, starburst}, month_numeric = {7} }

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A NIRCam-dark Galaxy Detected with the MIRI/F1000W Filter in the MIDIS/JADES Hubble Ultra Deep Field

Pablo G. Pérez-González, Pierluigi Rinaldi, Karina I. Caputi, and 32 more authors

The Astrophysical Journal Letters, Jul 2024

Abs DOI ADS arXiv

We report the discovery of Cerberus, an extremely red object detected with the MIRI Deep Imaging Survey (MIDIS) observations in the F1000W filter of the Hubble Ultra Deep Field. The object is detected at signal-to-noise ratio (S/N) \ensuremath∼ 6, with F1000W \ensuremath∼ 27 mag, and undetected in the NIRCam data gathered by the JWST Advanced Deep Extragalactic Survey (JADES), fainter than the 30.0–30.5 mag 5\ensuremathσ detection limits in individual bands, as well as in the MIDIS F560W ultradeep data (\ensuremath∼29 mag, 5\ensuremathσ). Analyzing the spectral energy distribution built with low-S/N (<5) measurements in individual optical-to-mid-infrared filters and higher-S/N (\ensuremath≳5) measurements in stacked NIRCam data, we discuss the possible nature of this red NIRCam-dark source using a battery of codes. We discard the possibility of Cerberus being a solar system body based on the <0.″016 proper motion in the 1 yr apart JADES and MIDIS observations. A substellar Galactic nature is deemed unlikely, given that the Cerberus’s relatively flat NIRCam-to-NIRCam and very red NIRCam-to-MIRI flux ratios are not consistent with any brown dwarf model. The extragalactic nature of Cerberus offers three possibilities: (1) a z \ensuremath∼ 0.4 galaxy with strong emission from polycyclic aromatic hydrocarbons—the very low inferred stellar mass, M _\ensuremath⋆ = 10^5–10^6 M _\ensuremath⊙, makes this possibility highly improbable; (2) a dusty galaxy at z \ensuremath∼ 4 with an inferred stellar mass M _\ensuremath⋆ \ensuremath∼ 10^8 M _\ensuremath⊙; and (3) a galaxy with observational properties similar to those of the reddest little red dots discovered around z \ensuremath∼ 7, but Cerberus lying at z \ensuremath∼ 15, with the rest-frame optical dominated by emission from a dusty torus or a dusty starburst.

@article{2024ApJ...969L..10P, author = {{P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Rinaldi}, Pierluigi and {Caputi}, Karina I. and {{\'A}lvarez-M{\'a}rquez}, Javier and {Annunziatella}, Marianna and {Langeroodi}, Danial and {Moutard}, Thibaud and {Boogaard}, Leindert and {Iani}, Edoardo and {Melinder}, Jens and {Costantin}, Luca and {{\"O}stlin}, G{\"o}ran and {Colina}, Luis and {Greve}, Thomas R. and {Wright}, Gillian and {Alonso-Herrero}, Almudena and {Bik}, Arjan and {Bosman}, Sarah E. I. and {Crespo G{\'o}mez}, Alejandro and {Dicken}, Daniel and {Eckart}, Andreas and {Garc{\'\i}a-Mar{\'\i}n}, Macarena and {Gillman}, Steven and {G{\"u}del}, Manuel and {Henning}, Thomas and {Hjorth}, Jens and {Jermann}, Iris and {Labiano}, {\'A}lvaro and {Meyer}, Romain A. and {Pei{\ensuremath{\beta}}ker}, Florian and {Pye}, John P. and {Ray}, Thomas P. and {Tikkanen}, Tuomo and {Walter}, Fabian and {van der Werf}, Paul P.}, title = {{A NIRCam-dark Galaxy Detected with the MIRI/F1000W Filter in the MIDIS/JADES Hubble Ultra Deep Field}}, journal = {\apjl}, keywords = {Galaxy formation, Galaxy evolution, High-redshift galaxies, Stellar populations, Broad band photometry, Galaxy ages, Active galactic nuclei, James Webb Space Telescope, 595, 594, 734, 1622, 184, 576, 16, 2291, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2024}, month = jul, volume = {969}, number = {1}, eid = {L10}, pages = {L10}, doi = {10.3847/2041-8213/ad517b}, archiveprefix = {arXiv}, eprint = {2402.16942}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...969L..10P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, jwst, non-agn, sed}, month_numeric = {7} }

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From Seeds to Supermassive Black Holes: Capture, Growth, Migration, and Pairing in Dense Protobulge Environments

Yanlong Shi, Kyle Kremer, and Philip F. Hopkins

The Astrophysical Journal Letters, Jul 2024

Abs DOI ADS arXiv

The origins and mergers of supermassive black holes (SMBHs) remain a mystery. We describe a scenario from a novel multiphysics simulation featuring rapid (\ensuremath≲1 Myr) hyper- Eddington gas capture by a \ensuremath∼1000 M _\ensuremath⊙ “seed” black hole (BH) up to supermassive (\ensuremath≳10^6 M _\ensuremath⊙) masses in a massive, dense molecular cloud complex typical of high-redshift starbursts. Due to the high cloud density, stellar feedback is inefficient, and most of the gas turns into stars in star clusters that rapidly merge hierarchically, creating deep potential wells. Relatively low- mass BH seeds at random positions can be “captured” by merging subclusters and migrate to the center in \ensuremath∼1 freefall time (vastly faster than dynamical friction). This also efficiently produces a paired BH binary with \ensuremath∼0.1 pc separation. The centrally concentrated stellar density profile (akin to a “protobulge”) allows the cluster as a whole to capture and retain gas and build up a large (parsec-scale) circumbinary accretion disk with gas coherently funneled to the central BH (even when the BH radius of influence is small). The disk is “hypermagnetized” and “flux-frozen”: dominated by a toroidal magnetic field with plasma \ensuremathβ \ensuremath∼ 10^‑3, with the fields amplified by flux-freezing. This drives hyper- Eddington inflow rates \ensuremath≳1 M _\ensuremath⊙ yr^‑1, which also drive the two BHs to nearly equal masses. The late-stage system appears remarkably similar to recently observed high-redshift “little red dots.” This scenario can provide an explanation for rapid SMBH formation, growth, and mergers in high-redshift galaxies.

@article{2024ApJ...969L..31S, author = {{Shi}, Yanlong and {Kremer}, Kyle and {Hopkins}, Philip F.}, title = {{From Seeds to Supermassive Black Holes: Capture, Growth, Migration, and Pairing in Dense Protobulge Environments}}, journal = {\apjl}, keywords = {Accretion, Black hole physics, Intermediate-mass black holes, Giant molecular clouds, Star formation, 14, 159, 816, 653, 1569, Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena}, year = {2024}, month = jul, volume = {969}, number = {2}, eid = {L31}, pages = {L31}, doi = {10.3847/2041-8213/ad5a95}, archiveprefix = {arXiv}, eprint = {2405.17338}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...969L..31S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, simulation, starburst, super-eddington, theory}, month_numeric = {7} }

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A Census of Photometrically Selected Little Red Dots at 4 < z < 9 in JWST Blank Fields

Vasily Kokorev, Karina I. Caputi, Jenny E. Greene, and 9 more authors

The Astrophysical Journal, Jun 2024

Abs DOI ADS arXiv

Observations with the James Webb Space Telescope (JWST) have uncovered numerous faint active galactic nuclei (AGN) at z \ensuremath∼ 5 and beyond. These objects are key to our understanding of the formation of supermassive black holes (SMBHs), their coevolution with host galaxies, as well as the role of AGN in cosmic reionization. Using photometric colors and size measurements, we perform a search for compact red objects in an array of blank deep JWST/NIRCam fields totaling \ensuremath∼640 arcmin^2. Our careful selection yields 260 reddened AGN candidates at 4 < z _phot < 9, dominated by a point-source-like central component (\ensuremath⟨r _eff\ensuremath⟩ < 130 pc) and displaying a dichotomy in their rest-frame colors (blue UV and red optical slopes). Quasar model fitting reveals our objects to be moderately dust-extincted (A _V \ensuremath∼ 1.6), which is reflected in their inferred bolometric luminosities of L _bol = 10^44–47 erg s^‑1 and fainter UV magnitudes M _UV ≃ ‑17 to ‑22. Thanks to the large areas explored, we extend the existing dusty AGN luminosity functions to both fainter and brighter magnitudes, estimating their number densities to be \texttimes100 higher than for UV-selected quasars of similar magnitudes. At the same time, they constitute only a small fraction of all UV-selected galaxies at similar redshifts, but this percentage rises to \ensuremath∼10% for M _UV \ensuremath∼ ‑ 22 at z \ensuremath∼ 7. Finally, assuming a conservative case of accretion at the Eddington rate, we place a lower limit on the SMBH mass function at z \ensuremath∼ 5, finding it to be consistent with both theory and previous JWST observations.

@article{2024ApJ...968...38K, author = {{Kokorev}, Vasily and {Caputi}, Karina I. and {Greene}, Jenny E. and {Dayal}, Pratika and {Trebitsch}, Maxime and {Cutler}, Sam E. and {Fujimoto}, Seiji and {Labb{\'e}}, Ivo and {Miller}, Tim B. and {Iani}, Edoardo and {Navarro-Carrera}, Rafael and {Rinaldi}, Pierluigi}, title = {{A Census of Photometrically Selected Little Red Dots at 4 < z < 9 in JWST Blank Fields}}, journal = {\apj}, keywords = {Galaxies, High-redshift galaxies, Active galaxies, Active galactic nuclei, 573, 734, 17, 16, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = jun, volume = {968}, number = {1}, eid = {38}, pages = {38}, doi = {10.3847/1538-4357/ad4265}, archiveprefix = {arXiv}, eprint = {2401.09981}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...968...38K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, agn-dominated, dust-reddened, jwst, photometry}, month_numeric = {6} }

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JWST’s ’Little Red Dots’ Offer Astronomers the Universe’s Weirdest Puzzle

Fabio Pacucci

Scientific American, Jun 2024

Abs ADS

The James Webb Space Telescope’s search for the earliest stars and black holes has yielded a very weird, very red, puzzle.

@article{2024SciAm.331E...1P, author = {{Pacucci}, Fabio}, title = {{JWST's 'Little Red Dots' Offer Astronomers the Universe's Weirdest Puzzle}}, journal = {Scientific American}, year = {2024}, month = jun, volume = {331}, pages = {E1}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024SciAm.331E...1P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, exotic physics, jwst, non-agn}, month_numeric = {6} }

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What Is the Nature of Little Red Dots and what Is Not, MIRI SMILES Edition

Pablo G. Pérez-González, Guillermo Barro, George H. Rieke, and 20 more authors

The Astrophysical Journal, Jun 2024

Abs DOI ADS arXiv

We study 31 little red dots (LRD) detected by JADES/NIRCam and covered by the SMILES/MIRI survey, of which \ensuremath∼70% are detected in the two bluest MIRI bands and 40% in redder MIRI filters. The median/quartiles redshifts are z=6.95.97.7 (55% spectroscopic). The spectral slopes flatten in the rest-frame near-infrared, consistent with a 1.6 \ensuremathμm stellar bump but bluer than direct pure emission from active galactic nuclei (AGN) tori. The apparent dominance of stellar emission at these wavelengths for many LRDs expedites stellar mass estimation: the median/quartiles are logM\ensuremath⋆/M\ensuremath⊙=9.49.19.7. The number density of LRDs is 10^‑4.0\ensuremath\pm0.1 Mpc^‑3, accounting for 14% \ensuremath\pm 3% of the global population of galaxies with similar redshifts and masses. The rest-frame near-/mid-infrared (2–4 \ensuremathμm) spectral slope reveals significant amounts of warm dust (bolometric attenuation \ensuremath∼3–4 mag). Our spectral energy distribution modeling implies the presence of 10 mag. We find a wide variety in the nature of LRDs. However, the best- fitting models for many of them correspond to extremely intense and compact starburst galaxies with mass-weighted ages 5–10 Myr, very efficient in producing dust, with their global energy output dominated by the direct (in the flat rest-frame ultraviolet and optical spectral range) and dust- recycled emission from OB stars with some contribution from an obscured AGN (in the infrared).

@article{2024ApJ...968....4P, author = {{P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Barro}, Guillermo and {Rieke}, George H. and {Lyu}, Jianwei and {Rieke}, Marcia and {Alberts}, Stacey and {Williams}, Christina C. and {Hainline}, Kevin and {Sun}, Fengwu and {Pusk{\'a}s}, D{\'a}vid and {Annunziatella}, Marianna and {Baker}, William M. and {Bunker}, Andrew J. and {Egami}, Eiichi and {Ji}, Zhiyuan and {Johnson}, Benjamin D. and {Robertson}, Brant and {Rodr{\'\i}guez Del Pino}, Bruno and {Rujopakarn}, Wiphu and {Shivaei}, Irene and {Tacchella}, Sandro and {Willmer}, Christopher N. A. and {Willott}, Chris}, title = {{What Is the Nature of Little Red Dots and what Is Not, MIRI SMILES Edition}}, journal = {\apj}, keywords = {Galaxy formation, Galaxy evolution, High-redshift galaxies, Galaxy stellar content, Stellar populations, Broad band photometry, Galaxy ages, James Webb Space Telescope, Active galactic nuclei, 595, 594, 734, 621, 1622, 184, 576, 2291, 16, Astrophysics - Astrophysics of Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics}, year = {2024}, month = jun, volume = {968}, number = {1}, eid = {4}, pages = {4}, doi = {10.3847/1538-4357/ad38bb}, archiveprefix = {arXiv}, eprint = {2401.08782}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...968....4P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, dust-reddened, jwst, sed, starburst}, month_numeric = {6} }

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The Galaxies Missed by Hubble and ALMA: The Contribution of Extremely Red Galaxies to the Cosmic Census at 3 < z < 8

Christina C. Williams, Stacey Alberts, Zhiyuan Ji, and 35 more authors

The Astrophysical Journal, Jun 2024

Abs DOI ADS arXiv

Using deep JWST imaging from JADES, JEMS, and SMILES, we characterize optically faint and extremely red galaxies at z > 3 that were previously missing from galaxy census estimates. The data indicate the existence of abundant, dusty, and poststarburst- like galaxies down to 10^8 M _\ensuremath⊙, below the sensitivity limit of Spitzer and the Atacama Large Millimeter/submillimeter Array (ALMA). Modeling the NIRCam and Hubble Space Telescope (HST) photometry of these red sources can result in extremely high values for both stellar mass and star formation rate (SFR); however, including seven MIRI filters out to 21 \ensuremathμm results in decreased masses (median 0.6 dex for log10(M\ensuremath*/M\ensuremath⊙) > 10) and SFRs (median 10\texttimes for SFR > 100 M _\ensuremath⊙ yr^‑1). At z > 6, our sample includes a high fraction of “little red dots” (LRDs; NIRCam- selected dust-reddened active galactic nucleus (AGN) candidates). We significantly measure older stellar populations in the LRDs out to rest-frame 3 \ensuremathμm (the stellar bump) and rule out a dominant contribution from hot dust emission, a signature of AGN contamination to stellar population measurements. This allows us to measure their contribution to the cosmic census at z > 3, below the typical detection limits of ALMA (L _IR < 10^12 L _\ensuremath⊙). We find that these sources, which are overwhelmingly missed by HST and ALMA, could effectively double the obscured fraction of the star formation rate density at 4 < z < 6 compared to some estimates, showing that prior to JWST, the obscured contribution from fainter sources could be underestimated. Finally, we identify five sources with evidence for Balmer breaks and high stellar masses at 5.5 < z < 7.7. While spectroscopy is required to determine their nature, we discuss possible measurement systematics to explore with future data.

@article{2024ApJ...968...34W, author = {{Williams}, Christina C. and {Alberts}, Stacey and {Ji}, Zhiyuan and {Hainline}, Kevin N. and {Lyu}, Jianwei and {Rieke}, George and {Endsley}, Ryan and {Suess}, Katherine A. and {Sun}, Fengwu and {Johnson}, Benjamin D. and {Florian}, Michael and {Shivaei}, Irene and {Rujopakarn}, Wiphu and {Baker}, William M. and {Bhatawdekar}, Rachana and {Boyett}, Kristan and {Bunker}, Andrew J. and {Cameron}, Alex J. and {Carniani}, Stefano and {Charlot}, Stephane and {Curtis-Lake}, Emma and {DeCoursey}, Christa and {de Graaff}, Anna and {Egami}, Eiichi and {Eisenstein}, Daniel J. and {Gibson}, Justus L. and {Hausen}, Ryan and {Helton}, Jakob M. and {Maiolino}, Roberto and {Maseda}, Michael V. and {Nelson}, Erica J. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Rieke}, Marcia J. and {Robertson}, Brant E. and {Saxena}, Aayush and {Tacchella}, Sandro and {Willmer}, Christopher N. A. and {Willott}, Chris J.}, title = {{The Galaxies Missed by Hubble and ALMA: The Contribution of Extremely Red Galaxies to the Cosmic Census at 3 < z < 8}}, journal = {\apj}, keywords = {High-redshift galaxies, Active galaxies, AGN host galaxies, 734, 17, 2017, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = jun, volume = {968}, number = {1}, eid = {34}, pages = {34}, doi = {10.3847/1538-4357/ad3f17}, archiveprefix = {arXiv}, eprint = {2311.07483}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...968...34W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust-reddened, early universe, jwst, sed, starburst}, month_numeric = {6} }

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Little Red Dots: An Abundant Population of Faint Active Galactic Nuclei at z \ensuremath∼ 5 Revealed by the EIGER and FRESCO JWST Surveys

Jorryt Matthee, Rohan P. Naidu, Gabriel Brammer, and 25 more authors

The Astrophysical Journal, Mar 2024

Abs DOI ADS arXiv

Characterizing the prevalence and properties of faint active galactic nuclei (AGNs) in the early Universe is key for understanding the formation of supermassive black holes (SMBHs) and determining their role in cosmic reionization. We perform a spectroscopic search for broad H\ensuremathα emitters at z \ensuremath≈ 4–6 using deep JWST/NIRCam imaging and wide field slitless spectroscopy from the EIGER and FRESCO surveys. We identify 20 H\ensuremathα lines at z = 4.2–5.5 that have broad components with line widths from \ensuremath∼1200–3700 km s^‑1, contributing \ensuremath∼30%–90% of the total line flux. We interpret these broad components as being powered by accretion onto SMBHs with implied masses \ensuremath∼10^7–8 M _\ensuremath⊙. In the UV luminosity range M _UV,AGN+host = ‑21 to ‑18, we measure number densities of \ensuremath≈10^‑5 cMpc^‑3. This is an order of magnitude higher than expected from extrapolating quasar UV luminosity functions (LFs). Yet, such AGN are found in only <1% of star-forming galaxies at z \ensuremath∼ 5. The number density discrepancy is much lower when compared to the broad H\ensuremathα LF. The SMBH mass function agrees with large cosmological simulations. In two objects, we detect complex H\ensuremathα profiles that we tentatively interpret as caused by absorption signatures from dense gas fueling SMBH growth and outflows. We may be witnessing early AGN feedback that will clear dust-free pathways through which more massive blue quasars are seen. We uncover a strong correlation between reddening and the fraction of total galaxy luminosity arising from faint AGN. This implies that early SMBH growth is highly obscured and that faint AGN are only minor contributors to cosmic reionization.

@article{2024ApJ...963..129M, author = {{Matthee}, Jorryt and {Naidu}, Rohan P. and {Brammer}, Gabriel and {Chisholm}, John and {Eilers}, Anna-Christina and {Goulding}, Andy and {Greene}, Jenny and {Kashino}, Daichi and {Labbe}, Ivo and {Lilly}, Simon J. and {Mackenzie}, Ruari and {Oesch}, Pascal A. and {Weibel}, Andrea and {Wuyts}, Stijn and {Xiao}, Mengyuan and {Bordoloi}, Rongmon and {Bouwens}, Rychard and {van Dokkum}, Pieter and {Illingworth}, Garth and {Kramarenko}, Ivan and {Maseda}, Michael V. and {Mason}, Charlotte and {Meyer}, Romain A. and {Nelson}, Erica J. and {Reddy}, Naveen A. and {Shivaei}, Irene and {Simcoe}, Robert A. and {Yue}, Minghao}, title = {{Little Red Dots: An Abundant Population of Faint Active Galactic Nuclei at z {\ensuremath{\sim}} 5 Revealed by the EIGER and FRESCO JWST Surveys}}, journal = {\apj}, keywords = {High-redshift galaxies, Quasars, Active galactic nuclei, Reionization, 734, 1319, 16, 1383, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2024}, month = mar, volume = {963}, number = {2}, eid = {129}, pages = {129}, doi = {10.3847/1538-4357/ad2345}, archiveprefix = {arXiv}, eprint = {2306.05448}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...963..129M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {abundance, agn-dominated, black hole mass, jwst, spectroscopy}, month_numeric = {3} }

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Unveiling Luminous Ly\ensuremathα Emitters at z \ensuremath≈ 6 through JWST/NIRCam Imaging in the COSMOS Field

Yuanhang Ning, Zheng Cai, Xiaojing Lin, and 7 more authors

The Astrophysical Journal Letters, Mar 2024

Abs DOI ADS arXiv

We study a sample of 14 spectroscopically confirmed Ly\ensuremathα emitters (LAEs) in the late era of reionization (at redshift z \ensuremath≈ 6) based on the JWST/NIRCam imaging data set. These LAEs with high Ly\ensuremathα luminosity of L(Ly\ensuremathα) \ensuremath∼10^42.4–10^43.4 erg s^‑1 have been covered by the (ongoing) COSMOS-Web survey over 0.28 deg^2 in four NIRCam bands (F115W, F150W, F277W, and F444W). With JWST/NIRCam imaging, we determine the UV continua with M _UV ranging from ‑20.5 to ‑18.5 mag. The UV slopes have a median value of \ensuremathβ \ensuremath≈ ‑2.35, and the steepest slopes can reach \ensuremathβ < ‑3. Under the excellent spatial resolution of JWST, we identify three objects in the sample as potential merging/interacting systems. The 14 LAEs (and their components) are compact in morphology, residing substantially below the mass–size relation of high-z galaxies. We further investigate their physical properties, including the stellar mass (M _*) and star formation rates (SFRs). Most of the LAEs lie on the SFR–M _* main-sequence relation, while two of them, featured as “little red dots,” likely host active galactic nuclei (AGNs), implying a \ensuremath∼10% AGN fraction. Moreover, we reveal that a new correlation may exist between Ly\ensuremathα equivalent width and the offset between Ly\ensuremathα and UV emission (\ensuremath∆d _Ly\ensuremathα ), with a median \ensuremath∆d _Ly\ensuremathα \ensuremath∼ 1 kpc. This could be explained by the Ly\ensuremathα radiative transfer process in both the interstellar medium and circumgalactic medium. The results usher in a new era of detailed analysis on high-z LAEs with the JWST capability.

@article{2024ApJ...963L..38N, author = {{Ning}, Yuanhang and {Cai}, Zheng and {Lin}, Xiaojing and {Zheng}, Zhen-Ya and {Feng}, Xiaotong and {Li}, Mingyu and {Li}, Qiong and {Spinoso}, Daniele and {Wu}, Yunjing and {Zhang}, Haibin}, title = {{Unveiling Luminous Ly{\ensuremath{\alpha}} Emitters at z {\ensuremath{\approx}} 6 through JWST/NIRCam Imaging in the COSMOS Field}}, journal = {\apjl}, keywords = {High-redshift galaxies, Lyman-alpha galaxies, Galaxy properties, Galaxy mergers, Active galactic nuclei, Reionization, 734, 978, 615, 608, 16, 1383, Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = mar, volume = {963}, number = {2}, eid = {L38}, pages = {L38}, doi = {10.3847/2041-8213/ad292f}, archiveprefix = {arXiv}, eprint = {2312.04841}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024ApJ...963L..38N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, early universe, jwst, morphology, spectroscopy}, month_numeric = {3} }

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2023

Little Red Dots or Brown Dwarfs? NIRSpec Discovery of Three Distant Brown Dwarfs Masquerading as NIRCam-selected Highly Reddened Active Galactic Nuclei

Danial Langeroodi and Jens Hjorth

The Astrophysical Journal Letters, Nov 2023

Abs DOI ADS arXiv

Cold, substellar objects such as brown dwarfs have long been recognized as contaminants in color-selected samples of active galactic nuclei (AGNs). In particular, their near- to mid-infrared colors (1-5 \ensuremathμm) can closely resemble the V-shaped (f _ \ensuremathλ ) spectra of highly reddened accreting supermassive black holes (“little red dots”), especially at 6 < z < 7. Recently, a NIRCam-selected sample of little red dots over 45 arcmin^2 has been followed up with deep NIRSpec multiobject prism spectroscopy through the UNCOVER program. By investigating the acquired spectra, we identify 3 of the 14 followed-up objects as T/Y dwarfs with temperatures between 650 and 1300 K and distances between 0.8 and 4.8 kpc. At 4.8_-0.1^+0.6 kpc, A2744-BD1 is the most distant brown dwarf discovered to date. We identify the remaining 11 objects as extragalactic sources at z _spec \ensuremath≳ 5. Given that three of these sources are strongly lensed images of the same AGN (A2744-QSO1), we derive a brown dwarf contamination fraction of 25% in this NIRCam selection of little red dots. We find that in the near-infrared filters, brown dwarfs appear much bluer than the highly reddened AGN, providing an avenue for distinguishing the two and compiling cleaner samples of photometrically selected highly reddened AGN.

@article{2023ApJ...957L..27L, author = {{Langeroodi}, Danial and {Hjorth}, Jens}, title = {{Little Red Dots or Brown Dwarfs? NIRSpec Discovery of Three Distant Brown Dwarfs Masquerading as NIRCam-selected Highly Reddened Active Galactic Nuclei}}, journal = {\apjl}, keywords = {Brown dwarfs, T dwarfs, Y dwarfs, Active galactic nuclei, 185, 1679, 1827, 16, Astrophysics - Astrophysics of Galaxies}, year = {2023}, month = nov, volume = {957}, number = {2}, eid = {L27}, pages = {L27}, doi = {10.3847/2041-8213/acfeec}, archiveprefix = {arXiv}, eprint = {2308.10900}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2023ApJ...957L..27L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {agn-dominated, dust-reddened, jwst, photometry, spectroscopy}, month_numeric = {11} }

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2022

Fourth Generation fermions as candidates for Dark Matter

Douglas Newman

arXiv e-prints, Jan 2022

Abs DOI ADS arXiv

Clifford Unification describes all the observed fundamental fermions in terms of seven commuting elements of the Cl_7,7 Clifford algebra. The eigenvalues of each commuting element define a binary quantum number, which relates to a fermion property that is conserved in decays and interactions. These include the quantum number descriptions of a hitherto unobserved fourth generation G(4) of fermions, which are predicted to have electric charges different to their observed G(1-3) counterparts. This, together with quantum number conservation, eliminates the possibility of interactions between G(4) and G(1-3) fermions. Neutral G(4) composites are shown to provide candidates for baryonic Dark Matter, which form the super- massive cores of galaxies. This identification could be examined in the light of recent observations of ’Little Red Dots’ in the early Universe. Neutral leptonic G(4) composites provide candidates for the Dark Matter component of galactic halos.

@article{2022arXiv220113238N, author = {{Newman}, Douglas}, title = {{Fourth Generation fermions as candidates for Dark Matter}}, journal = {arXiv e-prints}, keywords = {General Physics}, year = {2022}, month = jan, eid = {arXiv:2201.13238}, pages = {arXiv:2201.13238}, doi = {10.48550/arXiv.2201.13238}, archiveprefix = {arXiv}, eprint = {2201.13238}, primaryclass = {physics.gen-ph}, adsurl = {https://ui.adsabs.harvard.edu/abs/2022arXiv220113238N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, exotic physics, non-agn, theory}, month_numeric = {1} }

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About Awesome Little Red Dots

Awesome Little Red Dots (ALRD) is a collection of papers related to the study of “Little Red Dots” in astronomy. These are typically small, reddened objects that are often active galactic nuclei (AGNs) at high redshifts.

The bibliography is generated from a curated BibTeX file maintained in the ALRD GitHub repository.

For more information or to contribute, please visit the repository.