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Provides an in-depth analysis of one or a few specific LRD sources. Presents a list or table of LRD sources, candidates, or related objects with measured/derived properties. Uses computational models (hydrodynamical, cosmological, radiative transfer) to predict or interpret LRD properties. Primarily discusses theoretical models, physical mechanisms, or interpretations of LRD phenomena. Discusses or proposes scenarios other than AGN (e.g., compact starburst, mixed models) as the primary explanation for LRD properties. Investigates intense star formation activity as a primary or contributing factor to LRD properties. Investigates the role of dust extinction, reddening, or obscuration in shaping LRD properties or identification. Studies changes in brightness or spectral features of LRDs over time. Discusses observations or properties in the X-ray part of the electromagnetic spectrum. Focuses on the Spectral Energy Distribution (flux vs. wavelength), its shape (e.g., 'V-shape'), or modeling. Obtains or analyzes spectra (flux vs. wavelength at high resolution) to determine redshift, composition, kinematics. Utilizes observational data primarily from the James Webb Space Telescope or discusses JWST's role in LRD discovery/study. Utilizes observational data primarily from telescopes or surveys *other than* the James Webb Space Telescope (e.g., HST, Spitzer, ALMA, ground-based). Derives or analyzes source brightness measurements from images taken through different filters (e.g., SED fitting). Discusses observations or properties in the radio part of the electromagnetic spectrum. Combines data from significantly different spectral regions (e.g., Optical/IR + X-ray/Radio) for analysis. Pertains to cosmic epochs at high redshift (z > 4), the typical era where LRDs are found. Discusses potential counterparts or analogs to high-redshift LRDs found in the local or lower-redshift universe (e.g., z < 1). Discusses estimation or implications of the central supermassive black hole's mass, including SMBH growth. Analyzes the spatial distribution of LRDs or related objects to infer properties, environment, or connections. Analyzes spectral emission lines (e.g., Balmer, forbidden lines), their widths, ratios, or diagnostic power. Studies the properties (stellar mass, size, star formation rate, morphology) of the galaxy hosting the LRD. Examines the motion of gas or stars within the LRD or host galaxy, often derived from spectral line profiles. Focuses on the shape, size (e.g., effective radius), structure, or compactness of LRDs, usually from imaging. Describes the methods, criteria, or biases involved in identifying and selecting LRD candidates for study.

2025

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

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}, month_numeric = {10} }

Details
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

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}, 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

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}, 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

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}, 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} }

Details
AGN-heated dust revealed in “Little Red Dots”

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

arXiv e-prints, Sep 2025

Abs DOI ADS arXiv

Little Red Dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this Letter, we stack NIRCam, MIRI and ALMA images of a large and homogeneously- selected sample of LRDs from multiple JWST Legacy fields. We find clear evidence for hot-dust emission, seen as a rising mid- infrared continuum up to rest-frame λ_\rm rest∼3μm, that is best explained by a standard dusty AGN structure. This scenario holds regardless of whether the Optical/Ultraviolet (UV) continuum is stellar or AGN-dominated. Either ways, we argue that AGN-heated dust must have a geometry that leaves at least part of the Optical/UV continuum and broad-line region emission unobscured, which explains the observed blue UV slopes and prominent Balmer features. Lack of detections in the deep stack of X-ray images suggests that Compton-thick (N_\rm H>3\times10^24 cm^-2) gas obscuration is common, and likely confined within the dust sublimation radius (R_\rm sub\sim0.1 pc). While this gas-dust displacement is in line with recent models (e.g. the “Black Hole Star”), how pre-enriched hot dust can form around a nearly-pristine black hole environment remains to be explained.

@article{2025arXiv250907100D, 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 = {{AGN-heated dust revealed in ``Little Red Dots''}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.07100}, pages = {arXiv:2509.07100}, doi = {10.48550/arXiv.2509.07100}, archiveprefix = {arXiv}, eprint = {2509.07100}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250907100D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, multi-wavelength, sed, x-ray}, month_numeric = {9} }

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On the Fate of Little Red Dots

Andres Escala, Lucas Zimmermann, Sebastian Valdebenito, and 3 more authors

arXiv e-prints, Sep 2025

Abs ADS arXiv

We study the stability and possible fates of Little Red Dots, 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 study different scenarios for the evolution of Little Red Dots and conclude that in a fair fraction of those systems, the formation of a massive black hole by runaway collisions seems unavoidable, in all the possibilities studied within the stellar-only interpretation. We conclude that Little Red Dots are the most favourable known places to find a recently formed massive black hole seed, or in the process of formation, most probably formed directly in the supermassive range

@article{2025arXiv250920453E, author = {{Escala}, Andres and {Zimmermann}, Lucas and {Valdebenito}, Sebastian and {Vergara}, Marcelo C. and {Schleicher}, Dominik R. G. and {Liempi}, Matias}, title = {{On the Fate of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2025}, month = sep, eid = {arXiv:2509.20453}, pages = {arXiv:2509.20453}, archiveprefix = {arXiv}, eprint = {2509.20453}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250920453E}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, non-agn, simulation, starburst, theory}, month_numeric = {9} }

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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

arXiv e-prints, Sep 2025

Abs 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 their bolometric luminosities. We find evidence that more than half of the bolometric luminosity likely emerges in the rest-frame optical, with L_\rm bol/L_5100 = 5, roughly half the value for “standard” Active Galactic Nuclei. Meanwhile, the X-ray emitting corona, UV-emitting black-body, and reprocessed mid to far-infrared emission are all considerably sub-dominant, 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 ten 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 {\textbackslashbf (e.g., ∼10^5-10^7~\rm M_⊙ black holes, and ∼10^8~\rm M_⊙ galaxies)}, alleviating tensions with clustering, overmassive black holes, and the integrated black hole mass density in the Universe.

@article{2025arXiv250905434G, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = sep, eid = {arXiv:2509.05434}, pages = {arXiv:2509.05434}, archiveprefix = {arXiv}, eprint = {2509.05434}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250905434G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, jwst, multi-wavelength, sed}, month_numeric = {9} }

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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

arXiv e-prints, Sep 2025

Abs 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_\rm hrsim 10^10-11~M_⊙at redshifts z≃4-10, driving both rapid BH feeding and concurrent nuclear starbursts. As the BH grows to ∼10^6-7~M_⊙via super-Eddington accretion, the accretion power inflates a dense envelope whose effective temperature approaches the Hayashi limit at T_\rm eff≃5000~\rm K, producing red optical emission, while a coeval young stellar population of ∼10^7~M_⊙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_\rm opt/L_\rm UV≃2-10 from the onset of accretion bursts for ≃15~\rm 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{2025arXiv250919422I, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.19422}, pages = {arXiv:2509.19422}, archiveprefix = {arXiv}, eprint = {2509.19422}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250919422I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, sed, starburst, theory, x-ray}, month_numeric = {9} }

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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

arXiv e-prints, Sep 2025

Abs ADS arXiv

Recent photometric surveys with 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, the second most distant LRD known (z=8.5), with the JWST/NIRSpec 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 contains an overmassive black hole. However, our observed Balmer decrements imply negligible dust attenuation, resulting in a much lower Hbeta-based bolometric luminosity and Eddington luminosity (\raisebox-0.5ex\textasciitilde10%) than previously found. Lyman-alpha emission is strongly detected, implying f_esc,Lya\raisebox-0.5ex\textasciitilde30%. The extremely high [OIII]4363/Hgamma ratio is indicative of not only AGN photoionization and heating, but also extremely high densities (ne\raisebox-0.5ex\textasciitilde10\^7cm-3), suggesting that this black hole at such high redshift may be forming in an ultra-dense protogalaxy.

@article{2025arXiv250920455J, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.20455}, pages = {arXiv:2509.20455}, archiveprefix = {arXiv}, eprint = {2509.20455}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250920455J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst}, 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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Balmer Absorption in Iron Low-Ionization Broad Absorption Line Quasars

Karen M. Leighly, Sarah C. Gallagher, Hyunseop Choi, and 4 more authors

arXiv e-prints, Sep 2025

Abs DOI ADS arXiv

While C IV is the most common absorption line in Broad Absorption Line Quasar spectra, Balmer absorption lines are among the rarest. We present analysis of Balmer absorption in a sample of fourteen iron low-ionization BAL quasars (FeLoBALQs); eight are new identifications. We measured velocity offset, width, and apparent optical depth. The partial covering ubiquitous in BAL quasar spectra alters the measured Balmer optical depth ratios; taking that into account, 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 (H. Choi et al. 2022b), objects that are also found to have low accretion rates (K. M. Leighly et al. 2022; H. Choi et al. 2022a). Measures 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 \ensuremathαoi, the F\ensuremathλ point-to-point slope between 5100A and 3 microns. This parameter is strongly correlated with the Eddington ratio among low-redshift quasars (K. M. Leighly et al. 2024). Balmer absorption lines 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{2025arXiv250907611L, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.07611}, pages = {arXiv:2509.07611}, doi = {10.48550/arXiv.2509.07611}, archiveprefix = {arXiv}, eprint = {2509.07611}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250907611L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, spectroscopy, x-ray}, 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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Little Red Dots Are Nurseries of Massive Black Holes

Fabio Pacucci, Lars Hernquist, and Michiko Fujii

arXiv e-prints, Sep 2025

Abs ADS arXiv

The James Webb Space Telescope (JWST) has revealed a previously unknown population of compact, red galaxies at z ∼5, known as “Little Red Dots” (LRDs). With effective radii of ∼100 pc and stellar masses of 10^9-10^11  \rm M_⊙, a purely stellar interpretation implies extreme central densities, ρ_⋆\sim10^4-10^5  \rm M_⊙\,pc^-3 and in some cases up to ∼10^9  \rm M_⊙\,pc^-3, far exceeding those of globular clusters. At such densities, the dynamical friction time for 10  \rm M_⊙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\times10^3 < M_\rm VMS  [\rm M_⊙] < 5\times10^4 within <1 Myr. Once the supply of massive stars is depleted, the VMS contracts on a ∼8000 yr Kelvin-Helmholtz timescale and undergoes a general relativistic collapse, leaving a massive black hole of mass M_∙∼10^4  \rm M_⊙. 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{2025arXiv250902664P, author = {{Pacucci}, Fabio and {Hernquist}, Lars and {Fujii}, Michiko}, title = {{Little Red Dots Are Nurseries of Massive Black Holes}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2025}, month = sep, eid = {arXiv:2509.02664}, pages = {arXiv:2509.02664}, archiveprefix = {arXiv}, eprint = {2509.02664}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250902664P}, 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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What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?

Krisztina Perger, Judit Fogasy, and Sándor Frey

arXiv e-prints, Sep 2025

Abs 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{2025arXiv250903291P, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.03291}, pages = {arXiv:2509.03291}, archiveprefix = {arXiv}, eprint = {2509.03291}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250903291P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, non-agn, radio, starburst, theory}, month_numeric = {9} }

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

Remo Ruffini and Yu Wang

arXiv e-prints, Sep 2025

Abs ADS arXiv

Both the Galactic center and LRDs host million-solar-mass black holes within dense, cold reservoirs of molecular gas, 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{2025arXiv250917484R, author = {{Ruffini}, Remo and {Wang}, Yu}, title = {{Islands of Electromagnetic Tranquility in Our Galactic core and Little Red Dots that Shelter Molecules and Prebiotic Chemistry}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Earth and Planetary Astrophysics}, year = {2025}, month = sep, eid = {arXiv:2509.17484}, pages = {arXiv:2509.17484}, archiveprefix = {arXiv}, eprint = {2509.17484}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250917484R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, multi-wavelength, non-agn, spectroscopy, theory}, month_numeric = {9} }

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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, Sep 2025

Abs DOI ADS

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^\ensuremath-1 and a supermassive black hole mass of 5 \texttimes 10^8 M_\ensuremath⊙. 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^\ensuremath-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_\ensuremath⊙ ) =12 .0_\ensuremath-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.tmp..191S, 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 = sep, doi = {10.1038/s41550-025-02660-1}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NatAs.tmp..191S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {181512494}, lrdkeys = {black hole mass, clustering, dust, early universe, spectroscopy}, month_numeric = {9} }

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Do Little Red Dots Vary?

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

arXiv e-prints, Sep 2025

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 cast 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 2–4 times in a given waveband, 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 {\textbackslashsc nexus} campaign will detect changes in magnitude, Δm>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 {\textbackslashsc 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{2025arXiv250903571S, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.03571}, pages = {arXiv:2509.03571}, doi = {10.48550/arXiv.2509.03571}, archiveprefix = {arXiv}, eprint = {2509.03571}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250903571S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, simulation, variability, x-ray}, 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

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}, 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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Limitations on Morphological Fitting for JWST “Little Red Dots”

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

arXiv e-prints, Sep 2025

Abs ADS arXiv

Early results from JWST uncover a peculiar class of objects referred to as “little red dots” (LRDs). The extremely compact morphology of LRDs is often invoked to point towards an 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 SNR ≲25; 2) estimated PSF fraction could be a more robust physically-motivated description of LRD compactness; and 3) almost all permutations of modeled LRDs with SNR ≲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 Sersic and two-component fitting to a sample of observed LRDs to compare with our mock sample fitting. We find that \sim85% of observed LRDs are PSF-dominated, consistent with the AGN- dominated interpretation. The remaining \sim15% have low estimated PSF fractions (two-component fit) and sizes rsim 150 pc (Sersic). This morphological diversity of LRDs suggests that that the population likely is not homogeneous. It possibly has a primary subset of sources consistent with the AGN-dominated hypothesis, and a secondary population of sources more consistent with arising perhaps from extremely compact starbursts.

@article{2025arXiv250921236W, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2509.21236}, pages = {arXiv:2509.21236}, archiveprefix = {arXiv}, eprint = {2509.21236}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250921236W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, morphology, non-agn, simulation, starburst}, month_numeric = {9} }

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

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

arXiv e-prints, Sep 2025

Abs 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 non-radiative 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 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{2025arXiv250910638Z, 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: II. Super-Eddington Accretion}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena}, year = {2025}, month = sep, eid = {arXiv:2509.10638}, pages = {arXiv:2509.10638}, archiveprefix = {arXiv}, eprint = {2509.10638}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250910638Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, multi-wavelength, simulation, theory, x-ray}, 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

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}, month_numeric = {9} }

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Investigating Little Red Dots with UV Excess: Are They the High-Redshift Siblings of Blue Hot DOGs?

Lulu Bao, Chao-Wei Tsai, Jingwen Wu, and 7 more authors

arXiv e-prints, Aug 2025

Abs 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 hyper-luminous, 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 \textbackslashsim 1–4. In this study, we compare their multi-wavelength 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 appear 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 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{2025arXiv250821678B, 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 DOGs?}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.21678}, pages = {arXiv:2508.21678}, archiveprefix = {arXiv}, eprint = {2508.21678}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250821678B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, multi-wavelength, non-agn, sed}, month_numeric = {8} }

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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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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

arXiv e-prints, Aug 2025

Abs ADS arXiv

Little Red Dots (LRDs) are compact sources at z>5 discovered through JWST spectroscopy. Their spectra exhibit broad Balmer emission lines (rsim1000\rm~km~s^-1), alongside absorption features and a pronounced Balmer break – evidence for a dense, neutral hydrogen medium with the n=2 state. When interpreted as arising from AGN 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 n=2 state, Raman scattering of UV radiation by ground-state hydrogen, and Thomson scattering by free electrons. Using 3D Monte Carlo radiative transfer simulations with multi-branching resonance transitions, we examine their imprint on line shapes and ratios. Resonance scattering produces strong deviations from Case B flux ratios, clear differences between Hα and Hβ, and encodes gas kinematics in line profiles but cannot broaden Hβ due to conversion to Paα. While Raman scattering can yield broad wings, scattering of UV continuum is disfavored given the absence of strong FWHM variations across transitions. Raman scattering of higher Lyman-series emission can produce Hα/Hβ wing width ratios of rsim1.28, agreeing with observations. Thomson scattering can reproduce the observed rsim1000~\rm km\,s^-1 wings under plausible conditions, e.g., T_\rm e ∼10^4\rm \,K and N_\rm e\sim10^24\rm~cm^-2 – and lead to black hole mass overestimates by factors rsim10. Our results provide a framework for interpreting hydrogen lines in LRDs and similar systems.

@article{2025arXiv250808768C, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.08768}, pages = {arXiv:2508.08768}, archiveprefix = {arXiv}, eprint = {2508.08768}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250808768C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, simulation, spectroscopy, theory}, 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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Little Red Dots and their Progenitors from Direct Collapse Black Holes

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

arXiv e-prints, Aug 2025

Abs 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 compact morphology that gave them their name. A popular explanation is that they are a sub-population of active galactic nuclei/supermassive black holes (AGN/SMBHs) predominantly found in the high-redshift Universe (zrsim3). 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 sub- population. Here, we employ the semi-analytical 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 DCBH models agree better with 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 little 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-stellar mass ratios to further constrain the progenitors of LRDs.

@article{2025arXiv250814155J, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.14155}, pages = {arXiv:2508.14155}, archiveprefix = {arXiv}, eprint = {2508.14155}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250814155J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, jwst, sed, simulation, theory}, month_numeric = {8} }

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A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionization

Ignas Juodžbalis, Cosimo Marconcini, Francesco D’Eugenio, and 36 more authors

arXiv e-prints, Aug 2025

Abs ADS arXiv

Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad \textbackslashHalpha emitters with optically red continua, named Little Red Dots (LRDs), which comprise 15-30\% of the high redshift broad line AGN population. Due to their peculiar spectral properties and X-ray weakness, modeling LRDs with standard AGN templates has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black hole (BH) masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to 2 orders of magnitude, and other models claiming that LRDs may be entirely stellar in nature. We report the direct, dynamical BH mass measurement in a strongly lensed LRD at z = 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 BH mass estimates from the Balmer lines. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer M_\rm BH/M_*>2. Such a “naked” black hole, together with its near-pristine environment, indicates that this LRD is a massive black hole seed caught in its earliest accretion phase.

@article{2025arXiv250821748J, 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 {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 {Egami}, Eiichi and {Fabian}, Andrew and {Inayoshi}, Kohei and {Isobe}, Yuki and {Ivey}, Lucy and {Jones}, Gareth C. 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 {Perna}, Michele 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 the Epoch of Reionization}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.21748}, pages = {arXiv:2508.21748}, archiveprefix = {arXiv}, eprint = {2508.21748}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250821748J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, kinematics, spectroscopy}, month_numeric = {8} }

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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

arXiv e-prints, Aug 2025

Abs ADS arXiv

We discovered a hyperluminous dust-obscured galaxy with mysterious blue- excess emission (BlueDOG) in rest-frame UV of its spectral energy distribution (SED) from a multi-wavelength 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_⊙=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 supermassive black hole (SMBH) estimated using the extinction-corrected broad H\rmα emission line yields log M_\rm BH/M_⊙=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{2025arXiv250819618K, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.19618}, pages = {arXiv:2508.19618}, archiveprefix = {arXiv}, eprint = {2508.19618}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250819618K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, emission lines, sed, spectroscopy}, 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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MEGA: Spectrophotometric SED Fitting of Little Red Dots Detected in JWST MIRI

Kaila Ronayne, Casey Papovich, Allison Kirkpatrick, and 12 more authors

arXiv e-prints, Aug 2025

Abs 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-F444W > 1, but flat NIRCam-MIRI colors, -0.5 < F444W - F770W < 0.5, suggesting weak warm/hot dust components. The LRDs have -1.0 < F1000W - F1500W < 1.1, suggestive of non-uniform 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 stellar populations only; (2) active galactic nuclei (AGN) dominated models; and (3) composite AGN and star-forming models. Using the Bayesian information criterion, we find that six of the eight LRDs favor AGN models compared to star-forming models, though no model can fully reproduce all of the observed properties. Two LRDs with pronounced Balmer-breaks and broad H_α have SEDs that can be reproduced with hot, dense-gas (log T/K=5-5.7, log n/cm^-3 = 9-11) models with low dust attenuation (A(V)\raisebox-0.5ex~0.5mag). However, these models require an additional thermal component (800-1400K) to account for the MIRI data, and fail to reproduce the rest-UV and narrow [OIII] emission. The total bolometric emission from the dense-gas models, and possibly CIGALE AGN models, appear consistent with literature constraints in the far-IR and radio, and require log L_bol/L_⊙<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{2025arXiv250820177R, author = {{Ronayne}, Kaila and {Papovich}, Casey and {Kirkpatrick}, Allison and {Backhaus}, Bren E. and {Cullen}, Fergus and {Shen}, Lu and {Bagley}, Micaela B. 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 SED Fitting of Little Red Dots Detected in JWST MIRI}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.20177}, pages = {arXiv:2508.20177}, archiveprefix = {arXiv}, eprint = {2508.20177}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250820177R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, photometry, sed}, 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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Luminous Mid-IR Selected Obscured Quasars at Cosmic Noon in SDSS Stripe82 II: Spectroscopic Diversity and Broad Hα Emissions

Ben Wang, Yuzo Ishikawa, Joseph F. Hennawi, and 5 more authors

arXiv e-prints, Aug 2025

Abs ADS arXiv

We present a multiwavelength spectroscopic survey of 23 luminous mid- infrared-selected Type-2 quasars at redshifts z = 0.88 to 3.49. The targets were selected in the SDSS Stripe 82 field based on their bright WISE W4 detections (flux > 5 mJy) and extremely faint or red optical counterparts (e.g., r > 23 or r - W4 > 8.4), designed to identify heavily obscured quasars. Deep near- infrared (Gemini/GNIRS) and optical (Keck/LRIS and KCWI) spectroscopy confirm 23 out of 24 candidates as Type-2 quasars in this redshift range, including 12 objects at z > 2. The spectra exhibit strong rest-frame UV and optical emission lines (Ly-alpha, C IV, [O III], H-alpha) with a wide range of line widths, indicating significant spectral diversity. Approximately one-third of the sample (8 of 23) shows broad H-alpha emission (FWHM > 2000 km/s) despite their Type-2 classification, while the rest have only narrow lines (FWHM < 2000 km/s) characteristic of classical obscured quasars. Notably, these broad-line Type-2 quasars share similar spectral energy distributions with the JWST-discovered “little red dot” (LRD) AGNs, 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 angstrom emission is relatively weak for their high bolometric luminosities, deviating from trends seen in lower-redshift Type-2 QSOs. A new composite spectrum for Type-2 QSOs is built using our sample. Overall, our results demonstrate that mid-IR selection efficiently uncovers a diverse population of obscured quasars and that spectroscopic follow-up is crucial for revealing their true nature. This study provides new insights into heavily obscured SMBH growth at cosmic noon and bridges the gap to the obscured AGN populations now being revealed by JWST.

@article{2025arXiv250802792W, 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$α$ Emissions}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = aug, eid = {arXiv:2508.02792}, pages = {arXiv:2508.02792}, archiveprefix = {arXiv}, eprint = {2508.02792}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250802792W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, multi-wavelength, non-jwst, spectroscopy}, month_numeric = {8} }

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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

arXiv e-prints, Aug 2025

Abs 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 of LRDs. Our analysis first reveals a tension between the ionizing properties implied from Hα and HeII λ4686. The high Hα EWs require copious H-ionizing photons, more than the bluest AGN ionizing spectra can provide. In contrast, HeII emission is marginally detected, and its low EW is, at most, consistent with the softest AGN spectra. The low HeII/Hβ (\sim10^-2, 10) from gas/dust; and/or 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 immediate vicinity of local massive black holes. While previous studies have mostly focused on features dominated by the absorbing hydrogen cloud, the HeII- based diagnostic proposed here represents a crucial step toward understanding the central engine of LRDs.

@article{2025arXiv250818358W, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.18358}, pages = {arXiv:2508.18358}, archiveprefix = {arXiv}, eprint = {2508.18358}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250818358W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, non-agn, sed, spectroscopy, starburst}, 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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A Novel Formation Channel for Supermassive Black Hole Binaries in the Early Universe via Primordial Black Holes

Saiyang Zhang, Boyuan Liu, and Volker Bromm

arXiv e-prints, Aug 2025

Abs 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_\rm BH ∼10^6 M_⊙) 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 (LW) radiation from accreting PBHs suppresses H2 cooling, shifting the dominant gas coolant to atomic hydrogen. When combined with significant baryon–dark matter streaming velocities (v_\rm bχ rsim 0.8 σ_\rm bχ, where σ_\rm bχ is the root-mean- square streaming velocity), these effects facilitate the formation of dense, gravitationally unstable, atomically cooling gas clouds in the PBH wake. These clouds exhibit sustained high inflow rates (\dotM_\rm infall rsim 10^-2-10^-1 M_⊙\mathrmyr^-1), providing ideal conditions for DCBH formation from rapidly growing supermassive stars of ∼10^5 M_⊙at redshift z∼10-20. The resulting systems form SMBH binaries with initial mass ratios q∼O(0.1) and separations of ∼10 pc. Such PBH–DCBH binaries provide testable predictions for JWST and ALMA, potentially explaining high-z sources such as Little Red Dots, and represent gravitational-wave sources for future missions like LISA and TianQin, bridging early-Universe black hole physics, multi- messenger astronomy, and dark matter theory.

@article{2025arXiv250800774Z, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = aug, eid = {arXiv:2508.00774}, pages = {arXiv:2508.00774}, archiveprefix = {arXiv}, eprint = {2508.00774}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250800774Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, month_numeric = {8} }

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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

arXiv e-prints, Aug 2025

Abs ADS arXiv

The high-redshift (z>4) compact sources with “V-shaped” spectral energy distributions (SEDs), known as Little Red Dots (LRDs), are 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 applicable to reproduce AGN conventional variability, to study the variability of 22 LRDs in \textbackslashcitet{Tee2025}. 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 \lesssim30% of the observed luminosities, or they are intrinsically luminous AGNs. We use simulations to demonstrate the observational requirements to effectively investigate LRDs via variability: first, a sample of about 200 LRDs; second, each LRD has two observations separated by at least two years in the observed frame; third, the photometric uncertainty is ≤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{2025arXiv250816795Z, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = aug, eid = {arXiv:2508.16795}, pages = {arXiv:2508.16795}, archiveprefix = {arXiv}, eprint = {2508.16795}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250816795Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, sed, theory, variability}, month_numeric = {8} }

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Little Red Dots As Late-stage Quasi-stars

Mitchell C. Begelman and Jason Dexter

arXiv e-prints, Jul 2025

Abs 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 accreting from massive envelopes at a super-Eddington rate. We show that models of late-stage quasi- stars, with black hole masses exceeding ∼10% of the total, predict thermal and radiative properties that are insensitive to both black hole 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 black hole masses rsim 10^6 M_⊙, 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 black holes go through a quasi-star/LRD phase during their formation and growth.

@article{2025arXiv250709085B, author = {{Begelman}, Mitchell C. and {Dexter}, Jason}, title = {{Little Red Dots As Late-stage Quasi-stars}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = jul, eid = {arXiv:2507.09085}, pages = {arXiv:2507.09085}, archiveprefix = {arXiv}, eprint = {2507.09085}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250709085B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, theory, x-ray}, month_numeric = {7} }

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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

arXiv e-prints, Jul 2025

Abs ADS arXiv

One of JWST’s most remarkable discoveries is a population of compact red galaxies known as Little Red Dots (LRDs). Their existence raises many questions about their nature, origin, and evolution. These galaxies show a steep decline in number density-nearly two orders of magnitude-from z=6 to z=3. In this study, we explore their potential evolution by identifying candidate descendants in CEERS, assuming a single evolutionary path: the development of a blue star-forming outskirt around the red compact core. Our color-magnitude selection identifies galaxies as red as LRDs at z<4, surrounded by young, blue stellar outskirts. Morphological parameters were derived from single Sérsic profile fits; physical properties were obtained from SED fitting using a stellar-only model. These “post-LRD” candidates show LRD-like features with M_∗∼10^10 M_⊙, central densities ( Σ_∗∼10^11 M_⊙\textkpc^-2 ), compact sizes, and red rest-frame colors, but with an added extended component. Their number density at z = 3 \pm 0.5 ( ∼10^-4.15  \textMpc^-3 ) matches that of LRDs at 5 < z < 7 , supporting a possible evolutionary link. We observe a redshift-dependent increase in outskirts mass fraction and galaxy size-from ∼250 pc at z = 5 to ∼600 pc at z = 3 -suggesting global stellar growth. Meanwhile, the core remains red and compact, but the V-shape fades as the outskirts grow. These findings support an evolutionary scenario in which LRDs gradually acquire an extended stellar component over cosmic time by cold accretion. This may explain the apparent decline in their observed number density at lower redshift.

@article{2025arXiv250704011B, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2507.04011}, pages = {arXiv:2507.04011}, archiveprefix = {arXiv}, eprint = {2507.04011}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250704011B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, morphology, photometry, sample selection, sed}, month_numeric = {7} }

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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 3 more authors

arXiv e-prints, Jul 2025

Abs ADS arXiv

The majority of Little Red Dots (LRDs) hosting Active Galactic Nuclei (AGN) exhibits broad Hα emission, which recent studies propose originates from scattering off free electrons within an ionized and dense medium embedding the Broad Line Region (BLR), rather than directly from the BLR itself. This model suggests that the observed broad lines may be intrinsically narrower than observed, which would lead to black hole masses that are up to two orders of magnitude smaller than what inferred when assuming that the whole broad line comes from the BLR. To test this model, we present a joint analysis of multiple hydrogen recombination lines in the “Rosetta Stone”AGN, the brightest known LRD at z=2.26. We show that Hα, Hβ and Paβ have different spectral profiles, which is inconsistent with the predictions of the simple electron 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 surrounding the BLR is not universally applicable to LRDs and AGN, and therefore provides a counterexample to the claim of a universal and systematic overestimation of black hole masses.

@article{2025arXiv250708929B, author = {{Brazzini}, Matilde and {D'Eugenio}, Francesco and {Maiolino}, Roberto and {Juod{\v{z}}balis}, Ignas and {Ji}, Xihan and {Scholtz}, Jan}, title = {{Ruling out dominant electron scattering in Little Red Dots' Rosetta Stone using multiple hydrogen lines}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2507.08929}, pages = {arXiv:2507.08929}, archiveprefix = {arXiv}, eprint = {2507.08929}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250708929B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, non-agn, spectroscopy, theory}, month_numeric = {7} }

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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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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

arXiv e-prints, Jul 2025

Abs ADS arXiv

Recent JWST observations 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 z > 4 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 z = 0.1, 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 km/s), 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 [FeII] emission lines indicative of low-ionization gas, which we find also present in an JWST-selected LRD at z = 2.26. We find small but statistically significant variability in Hα consistent with previous findings. Finally, with the new X-ray observation from NuSTAR, we confirm the extreme X-ray weakness of this LRD, which might imply Compton-thick gas obscuration with N_\rm H>10^24~\rm cm^-2. 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{2025arXiv250723774J, author = {{Ji}, Xihan and {D'Eugenio}, Francesco and {Juod{\v{z}}balis}, Ignas and {Walton}, Dom 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2507.23774}, pages = {arXiv:2507.23774}, archiveprefix = {arXiv}, eprint = {2507.23774}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250723774J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, local counterpart, spectroscopy, variability, x-ray}, month_numeric = {7} }

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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

arXiv e-prints, Jul 2025

Abs ADS arXiv

Recently discovered supermassive black holes with masses of \sim10^8 M_⊙at redshifts z\sim9-11 in active galactic nuclei (AGN) 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 halos and grow up to <10^6 M_⊙. 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 is informed by stellar evolution and general relativistic SMS collapse simulations. We find that SMS explosion light curves reach a brightness \sim10^45\mathrm-47\,\mathrmerg/s and last 10-200 years in the source frame - up to 250-3000 years with cosmic time dilation. This makes them quasi-persistent sources which vary indistinguishably to little red dots and AGN within 0.5-9\,(1+z) yrs. Bright SMS explosions are observable in long-wavelength JWST filters up to z\leq20 (24-26 mag) and pulsating SMSs up to z\leq15. EUCLID and the Roman space telescope (RST) can detect SMS explosions at z<11-12. Their deep fields could constrain the SMS rate down to 10^-11Mpc^-3yr^-1, 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{2025arXiv250715556J, 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 = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2507.15556}, pages = {arXiv:2507.15556}, archiveprefix = {arXiv}, eprint = {2507.15556}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250715556J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, non-jwst, simulation, variability}, month_numeric = {7} }

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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 24 more authors

arXiv e-prints, Jul 2025

Abs ADS arXiv

JWST observations have revealed a population of high-redshift “little red dots” (LRDs) that challenge conventional AGN models. We report the discovery of three local LRDs at z = 0.1-0.2, initially selected from the SDSS 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 SED, 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 Hα 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, Fe II, and Ca II triplet absorption lines, suggesting the presence of a cool (\sim5000 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. The WISE-detected IR emission is consistent with weak dust emission of T ∼10^2-10^3 K. We propose a conceptual model consisting of a largely thermalized cool-gas envelope surrounding the central black hole and an extended emission line region with high-density outflowing gas to explain the observed properties of these local LRDs.

@article{2025arXiv250710659L, 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}, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, Solar and Stellar Astrophysics}, year = {2025}, month = jul, eid = {arXiv:2507.10659}, pages = {arXiv:2507.10659}, archiveprefix = {arXiv}, eprint = {2507.10659}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250710659L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, local counterpart, photometry, sed, spectroscopy}, 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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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

arXiv e-prints, Jul 2025

Abs 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 \sim5000\rm~K. Meanwhile, many LRD spectra exhibit a Balmer break, often attributed to absorption by a dense gas shell surrounding an AGN. Using semi-analytical 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, ρ<10^-9\rm~g~cm^-3, implies a significant opacity contrast even at a cool photosphere temperature of \sim5000\rm~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 4000\rm~K≲T_\rm eff\lesssim6000\rm~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 predictions of our model and the prospects for more realistic spectra based on super- Eddington accretion simulations.

@article{2025arXiv250707190L, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2507.07190}, pages = {arXiv:2507.07190}, archiveprefix = {arXiv}, eprint = {2507.07190}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250707190L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, non-agn, sed, spectroscopy, theory}, 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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Supermassive Stars Match the Spectral Signatures of JWST’s Little Red Dots

Devesh Nandal and Abraham Loeb

arXiv e-prints, Jul 2025

Abs 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 non-rotating, metal-free 10^6 \,M_⊙SMS. We establish that its luminosity (L_λ≈1.7 \times 10^44  \texterg  \texts^-1 \,μ\textm^-1 at 4050 Angstroms) provides a decisive constraint, matching prominent LRDs. Our model self-consistently reproduces their defining spectral features: the extreme, V-shaped Balmer break is an intrinsic photospheric effect, while the complex line phenomenology, strong Hβ in emission with other Balmer lines in absorption arises from non-LTE effects in a single stellar atmosphere. Applying physically motivated broadening, our spectrum provides an excellent quantitative match to LRDs at both high (z=7.76) and low (z=3.55) redshift. Our model provides a simple, self-consistent physical picture for LRDs, offering a compelling alternative to multi-component obscured AGN scenarios and suggesting we may be directly witnessing the final, luminous moments of an SMBH progenitor before its ultimate collapse.

@article{2025arXiv250712618N, author = {{Nandal}, Devesh and {Loeb}, Abraham}, title = {{Supermassive Stars Match the Spectral Signatures of JWST's Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Solar and Stellar Astrophysics}, year = {2025}, month = jul, eid = {arXiv:2507.12618}, pages = {arXiv:2507.12618}, archiveprefix = {arXiv}, eprint = {2507.12618}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250712618N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, non-agn, sed, spectroscopy, theory}, 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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Little Red Dots from Ultra-Strongly Self-Interacting Dark Matter

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

arXiv e-prints, Jul 2025

Abs 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 rsim 10^5 M_⊙at redshifts z rsim 5. We develop a semi-analytic model that tracks the evolution of the dark matter halo population, the redshift of collapse z_\rm 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 ∼5 shows excellent agreement with LRD observational data and SIDM merger-tree simulations, particularly at the high-mass end (m_\rm BH rsim 10^7 M_⊙). 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{2025arXiv250703230R, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2507.03230}, pages = {arXiv:2507.03230}, archiveprefix = {arXiv}, eprint = {2507.03230}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250703230R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, early universe, non-agn, theory}, 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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Discovery of a Little Red Dot candidate at zrsim10 in COSMOS-Web based on MIRI-NIRCam selection

Takumi S. Tanaka, Hollis B. Akins, Yuichi Harikane, and 60 more authors

arXiv e-prints, Jul 2025

Abs 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 \sim5\,\rm μm and is insufficient to capture the characteristic V-shaped spectral energy distributions (SEDs) of LRDs. In this study, we present the first search for zrsim10 LRD candidates using both NIRCam and MIRI imaging from COSMOS-Web, which provides the largest joint NIRCam-MIRI coverage to date (0.20\,\rm deg^2). Taking advantage of MIRI/F770W to remove contaminants, we identify one robust candidate, CW-LRD-z10 at z_\rm phot=10.5^+0.7_-0.6 with M_\rm UV=-19.9^+0.1_-0.2\,\rm mag. CW-LRD-z10 exhibits a compact morphology, a distinct V-shaped SED, and a non-detection in F115W, all consistent with being an LRD at z\sim10. Based on this discovery, we place the first constraint on the number density of LRDs at z\sim10 with M_\rm UV∼-20 of 1.2^+2.7_-1.0\times10^-6\,\rm Mpc^-3 mag^-1, suggesting that the fraction of LRDs among the overall galaxy population increases with redshift, reaching \sim3% at z\sim10. 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{2025arXiv250800057T, 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 and {Kokorev}, Vasily and {Shuntov}, Marko and {Koekemoer}, Anton M. and {Franco}, Maximilien and {Liu}, Daizhong and {Taylor}, Anthony J. and {Kartaltepe}, Jeyhan S. and {Bosman}, Sarah E. and {Champagne}, Jaclyn B. and {Kakiichi}, Koki 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}, Ming-Yang 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}, A. J. and {Gillman}, Steven and {Khostovan}, Ali Ahmad and {Long}, Arianna S.}, title = {{Discovery of a Little Red Dot candidate at $zrsim10$ in COSMOS-Web based on MIRI-NIRCam selection}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2508.00057}, pages = {arXiv:2508.00057}, archiveprefix = {arXiv}, eprint = {2508.00057}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250800057T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, photometry, sed}, month_numeric = {7} }

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A deep dive down the broad-line region: permitted OI, CaII and FeII emission in an AGN Little Red Dot at z=5.3

Roberta Tripodi, Maruša Bradač, Francesco D’Eugenio, and 23 more authors

arXiv e-prints, Jul 2025

Abs ADS arXiv

We present a spectroscopic analysis of a broad-line active galactic nucleus (AGN) selected as little red dot at z = 5.3 behind the Bullet cluster (Bz5.3), based on JWST/NIRCam and NIRSpec data. The detection of strong FeII, OI, and CaII triplet emission lines, along with the evidence of broad Balmer lines, provides unambiguous evidence of a broad-line region (BLR) and an accreting supermassive black hole. Notably, we report the first detection of the \lambda1304 bump (i.e., blend of OIλ1304 and SiII) at high redshift, a feature commonly seen in local AGNs but not yet reported in the early Universe. The OIλ1304/\lambda8446 photon ratio is highly suppressed (0.1-0.3), implying significant internal dust extinction, with estimated dust attenuation A_V ∼0.4-1.0. We identify Lyβ fluorescence as the dominant excitation mechanism of the low-ionization lines, with additional contributions from collisional excitation. High OIλ8446 equivalent width and weak OIλ7774 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 OIλ8446 and CaII 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{2025arXiv250720684T, 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 {Asada}, Yoshihisa and {Calabr{\`o}}, Antonello 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 {Markov}, Vladan and {Merida}, Rosa M. and {Napolitano}, Lorenzo and {Noirot}, G{\"a}el 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 OI, CaII and FeII emission in an AGN Little Red Dot at z=5.3}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jul, eid = {arXiv:2507.20684}, pages = {arXiv:2507.20684}, archiveprefix = {arXiv}, eprint = {2507.20684}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250720684T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, early universe, emission lines, jwst, spectroscopy}, 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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Little Red Dots as self-gravitating discs accreting on supermassive stars: Spectral appearance and formation pathway of the progenitors to direct collapse black holes

Lorenz Zwick, Christopher Tiede, and Lucio Mayer

arXiv e-prints, Jul 2025

Abs ADS arXiv

We propose an alternative physical interpretation and formation pathway for the recently discovered “little red dots” (LRDs). We model LRDs as super-massive stars (SMSs) surrounded by massive self- gravitating accretion discs (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 AGN, stellar wind, dust obscuration or galactic component is required. This results in a model with uniquely few, physically motivated free parameters that are robust to variations in observed LRD properties. We perform MCMC 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 discs, and the recovered SMS masses of few 10^6 M_⊙ imply the subsequent formation of massive black holes (BH) that squarely follow the expected BH mass–galaxy mass relation. In addition, the model implies a redshift distribution for LRDs that accurately matches with observations.

@article{2025arXiv250722014Z, author = {{Zwick}, Lorenz and {Tiede}, Christopher and {Mayer}, Lucio}, title = {{Little Red Dots as self-gravitating discs accreting on supermassive stars: Spectral appearance and formation pathway of the progenitors to direct collapse black holes}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2025}, month = jul, eid = {arXiv:2507.22014}, pages = {arXiv:2507.22014}, archiveprefix = {arXiv}, eprint = {2507.22014}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250722014Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, non-agn, sed, spectroscopy, 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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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 32 more authors

arXiv e-prints, Jun 2025

Abs ADS arXiv

We present a broad-line active galactic nucleus (AGN) at z = 5.077, observed with both NIRSpec/MSA and NIRSpec/IFU by the JADES and BlackTHUNDER surveys. The target exhibits all the hallmark features of a ’Little Red Dot’ (LRD) AGN. The combination of spatially resolved and high-resolution spectroscopy offers deeper insight into its nature. The Hα line has multiple components, including two broad Gaussians, yielding a black-hole mass of \log(M_\rm BH/M_⊙) = 7.65, while the narrow [O III]λ5007 gives a galaxy dynamical mass of \log(M_\rm dyn/M_⊙) = 9.1, suggesting a dynamically overmassive black hole relative to the host galaxy. The target has two satellites, and is immersed in a 7-kpc wide pool of ionized gas. A spatially detached outflow is also tentatively detected. Hα shows strong absorption with high equivalent width (EW), ruling out a stellar origin, and with velocity and velocity dispersion of v = -13 km s^-1 and σ = 120 km s^-1. There is tentative evidence (2.6 σ) of temporal variability in the EW of the Hα absorber over two rest-frame months. If confirmed, this would suggest a highly dynamic environment. Notably, while the Hα 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. In this context, 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 of cyclic expansion and contraction of the gas around the SMBH.

@article{2025arXiv250614870D, 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 {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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jun, eid = {arXiv:2506.14870}, pages = {arXiv:2506.14870}, archiveprefix = {arXiv}, eprint = {2506.14870}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250614870D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, spectroscopy, variability}, 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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RUBIES: A Spectroscopic Census of Little Red Dots; All V-Shaped Point Sources Have Broad Lines

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

arXiv e-prints, Jun 2025

Abs ADS arXiv

The physical nature of Little Red Dots (LRDs) - a population of compact, red galaxies revealed by JWST - remains unclear. Photometric samples are constructed from varying selection criteria with limited spectroscopic follow-up available to test intrinsic spectral shapes and prevalence of broad emission lines. We use 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 \sim1500 galaxies at z > 3.1. We identify 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 emerges 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 compare the spectroscopic LRD sample to published photometric searches. Although these selections have high accuracy, down to \rm F444W<26.5, only 50-62% of the RUBIES LRDs were previously identified. 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{2025arXiv250605459H, 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}, title = {{RUBIES: A Spectroscopic Census of Little Red Dots; All V-Shaped Point Sources Have Broad Lines}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jun, eid = {arXiv:2506.05459}, pages = {arXiv:2506.05459}, archiveprefix = {arXiv}, eprint = {2506.05459}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250605459H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, sample selection, sed, spectroscopy}, 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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A big red dot at cosmic noon

Federica Loiacono, Roberto Gilli, Marco Mignoli, and 22 more authors

arXiv e-prints, Jun 2025

Abs ADS arXiv

We report the discovery of a little red dot (LRD), dubbed BiRD (’big red dot’), at z=2.33 in the field around the z=6.3 quasar SDSSJ1030+0524. Using NIRCam images, we identified it as a bright outlier in the F200W-F356W color vs F356W magnitude diagram of point sources in the field. The NIRCam/WFSS spectrum reveals the emission from HeIλ10830 and PaG line, both showing a narrow and a broad (FWHMrsim 2000 \rm kms^-1) component. The HeI line is affected by an absorption feature, tracing dense gas with HeI column density in the 2^3S level N∼0.5-1.2\times 10^14\rm cm^-2, depending on the location of the absorber, which is outflowing at the speed of Δv ∼-830 \rm kms^-1. As observed in the majority of LRDs, BiRD does not show X-ray or radio emission. The BH mass and the bolometric luminosity, both inferred from the PaG broad component, amount to M_\rm BH∼10^8\rm M_⊙ and L_\rm bol∼2.9\times 10^45\rm ergs^-1, respectively. Intriguingly, BiRD presents strict analogies with other two LRDs spectroscopically confirmed at cosmic noon, GN-28074 (“Rosetta Stone”) at z=2.26 and RUBIES-BLAGN-1 at z=3.1. The blueshifted HeI absorption detected in all three sources suggests that gas outflows may be common in LRDs. We derive a first estimate of the space density of LRDs at z<3 based on JWST data, as a function of L_\rm bol and BH mass. The space density is only a factor of ∼2-3 lower than that of UV- selected quasars with comparable L_\rm bol and z, meaning that the contribution of LRDs to the broader AGN population is also relevant at cosmic noon. A similar trend is also observed in terms of BH masses. If, as suggested by recent theories, LRDs probe the very first and rapid growth of black hole seeds, our finding may suggest that the formation of black hole seeds remains efficient at least up to cosmic noon.

@article{2025arXiv250612141L, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jun, eid = {arXiv:2506.12141}, pages = {arXiv:2506.12141}, archiveprefix = {arXiv}, eprint = {2506.12141}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250612141L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, multi-wavelength, spectroscopy}, 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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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

arXiv e-prints, Jun 2025

Abs 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 (MAD) 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 (LRDs) recently discovered by JWST.

@article{2025arXiv250602289Z, 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 = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena}, year = {2025}, month = jun, eid = {arXiv:2506.02289}, pages = {arXiv:2506.02289}, archiveprefix = {arXiv}, eprint = {2506.02289}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250602289Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, jwst, sed, simulation, x-ray}, month_numeric = {6} }

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JWST Insights into Narrow-line Little Red Dots

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

arXiv e-prints, Jun 2025

Abs ADS arXiv

James Webb Space Telescope (JWST) has revealed a population of red and compact objects with a unique V-shape SED at z >= 4 known as Little Red Dots (LRDs). Most of the LRDs with existing spectral observations exhibit broad Balmer lines and are thus likely to host active galactic nuclei (AGNs). Here we present a study of LRDs with no broad H-alpha component. Our sample consists of five LRDs at z\raisebox-0.5ex\textasciitilde5 with H-alpha line widths of about 250 km/s. They are selected from 32 LRDs that have NIRSpec high- or medium-resolution grating spectra covering H-alpha. During our construction of the sample, we find that approximately 20 percent of the LRD candidates previously selected do not show red continuum emission but resemble the V-shape spectra due to strong line emission. Compared to normal star-forming galaxies, narrow-line LRDs tend to have relatively higher H-alpha line widths and luminosities. If these LRDs are dominated by galaxies, our SED modeling suggests that they are dusty, compact star-forming galaxies with high stellar masses and star formation rates (SFRs). Alternatively, if their SEDs are produced by AGNs, the inferred central black hole masses (MBH) are in the range of 10\^5 to 10\^6 solar masses, placing 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 measurement uncertainties, these black holes appear slightly overmassive relative to the local MBH-Mstar relation, but consistent or undermassive with respect to the MBH-sigma and MBH-Mdyn relations. We further find that nearly half of the high-redshift broad-line AGNs exhibit V-shape SEDs. (abridged)

@article{2025arXiv250604350Z, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jun, eid = {arXiv:2506.04350}, pages = {arXiv:2506.04350}, archiveprefix = {arXiv}, eprint = {2506.04350}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250604350Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, sed, spectroscopy}, 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}, year = {2025}, month = may, volume = {984}, number = {2}, eid = {L55}, pages = {L55}, doi = {10.3847/2041-8213/adce6c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...984L..55B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, theory, variability}, altmetric = {172805119}, eprint = {2501.03309}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {5} }

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Dust Budget Crisis in Little Red Dots

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

arXiv e-prints, May 2025

Abs 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 rsim 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 re-evaluate 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 the JWST MIRI, Herschel, and ALMA, our analysis finds that the visual extinction is tightly constrained to A_V ≲1.0 mag for A2744-45924 and A_V ≲1.5 mag for RUBIES- BLAGN-1 under the SMC extinction laws, with slightly weaker constraints for those with gray extinction in the UV range. The revised A_V values yield a radiative efficiencies of 10% for the LRD population, easing the tension with the Soltan 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 their natures, environments, and evolutionary pathways of massive black holes in the early universe.

@article{2025arXiv250522600C, author = {{Chen}, Kejian and {Li}, Zhengrong and {Inayoshi}, Kohei and {Ho}, Luis C.}, title = {{Dust Budget Crisis in Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = may, eid = {arXiv:2505.22600}, pages = {arXiv:2505.22600}, archiveprefix = {arXiv}, eprint = {2505.22600}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250522600C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, early universe, jwst, multi-wavelength, sed}, 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

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}, 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

arXiv e-prints, May 2025

Abs DOI ADS arXiv

Little red dots (LRDs) are a newly identified class of broad-line active galactic nuclei (AGN) with a distinctive v-shape spectrum characterized by red optical and blue UV continuum emission. Their high abundance at redshifts of z\sim6-8 and decline at lower redshifts suggest a transient origin. We propose that the spectral shape of LRDs originates from compact binary black hole systems, where each black hole is surrounded by a mini-disk and embedded in a larger circum-binary disk. With a binary separation of ≲10^3 Schwarzschild radii, the Wien tail of a T≃5000~\rm K blackbody spectrum at the inner edge of the circum-binary disk produces the red optical emission, while the mini-disks power the UV continuum. Binary torques carve out a gap between the circum-binary disk and 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≲1 mag), resolving overestimated luminosities for LRDs in previous studies and alleviating a tension with the so-called Soltan argument. This model predicts a distinct spectral evolution as the binary orbit decays through binary-disk interactions and gravitational waves (GWs), linking early-stage “proto-LRD” binaries to the broader AGN population and late-stage “LRD- descendants” to coalescing binaries detectable in GW experiments.

@article{2025arXiv250505322I, author = {{Inayoshi}, Kohei and {Shangguan}, Jinyi and {Chen}, Xian and {Ho}, Luis C. and {Haiman}, Zoltan}, title = {{The Emergence of Little Red Dots from Binary Massive Black Holes}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Astrophysics of Galaxies}, year = {2025}, month = may, eid = {arXiv:2505.05322}, pages = {arXiv:2505.05322}, doi = {10.48550/arXiv.2505.05322}, archiveprefix = {arXiv}, eprint = {2505.05322}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250505322I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, multi-wavelength, sed, theory}, month_numeric = {5} }

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Black Hole Envelopes in Little Red Dots

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

arXiv e-prints, May 2025

Abs ADS arXiv

Recent observations by the James Webb Space Telescope have uncovered a population of compact, red object (z∼4\text–7) known as little red dots (LRDs). The presence of broad Balmer emission lines indicates 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 ∼1 M_⊙~\rm yr^-1. A photosphere emerges either within the envelope or in the infalling medium, with a characteristic temperature of 5000 - 7000 \rm K, 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, ∼0.01~\rm 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{2025arXiv250506965K, 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 = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Astrophysics of Galaxies}, year = {2025}, month = may, eid = {arXiv:2505.06965}, pages = {arXiv:2505.06965}, archiveprefix = {arXiv}, eprint = {2505.06965}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250506965K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, theory, variability, x-ray}, month_numeric = {5} }

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X-ray properties of compact elliptical galaxies

Orsolya E. Kovacs, Norbert Werner, Akos Bogdan, and 1 more author

arXiv e-prints, May 2025

Abs 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 α/\rmFe 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_⋆-L_X relation and occupying the lower boundary of the M_⋆-M_\rm 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{2025arXiv250514768K, author = {{Kovacs}, Orsolya E. and {Werner}, Norbert and {Bogdan}, Akos and {de Plaa}, Jelle}, title = {{X-ray properties of compact elliptical galaxies}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = may, eid = {arXiv:2505.14768}, pages = {arXiv:2505.14768}, archiveprefix = {arXiv}, eprint = {2505.14768}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250514768K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, local counterpart, morphology, multi-wavelength, x-ray}, month_numeric = {5} }

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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

arXiv e-prints, May 2025

Abs 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 ≤z ≤8) in ASTRID, and find seventeen which fit the color and size criteria of LRDs. These LRDs are galaxies with high stellar masses (\rm log(M_*/M_⊙) ≥9.7), and massive black holes (\rm log(M_BH/M_⊙) ≥6.8). The host galaxies are dense, with stellar half mass radii (\rm 325 pc ≤r_\rm half,* ≤620 pc), 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 23.5-25.5. 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 their host galaxies having typical dust levels and relatively high star formation rates accompanying their highly accreting black holes, resulting in their spectra being too flat.

@article{2025arXiv250520439L, author = {{LaChance}, Patrick and {Croft}, Rupert A. C. and {Di Matteo}, Tiziana 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 = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies}, year = {2025}, month = may, eid = {arXiv:2505.20439}, pages = {arXiv:2505.20439}, archiveprefix = {arXiv}, eprint = {2505.20439}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250520439L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, early universe, host galaxy, simulation}, 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 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}, 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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A black hole in a near-pristine galaxy 700 million years after the Big Bang

Roberto Maiolino, Hannah Uebler, Francesco D’Eugenio, and 36 more authors

arXiv e-prints, May 2025

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 [OIII]5007 emission line relative to the narrow Hβ emission indicates extremely low metallicity, less than 10^-2 solar. 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{2025arXiv250522567M, author = {{Maiolino}, Roberto and {Uebler}, Hannah and {D'Eugenio}, Francesco and {Scholtz}, Jan and {Juodzbalis}, 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 {Cresci}, Giovanni and {Curti}, Mirko and {Fabian}, Andrew C. and {Katz}, Harley and {Kumari}, Nimisha and {Laporte}, Nicolas and {Mazzolari}, Giovanni and {Robertson}, Brant and {Sun}, Fengwu and {Rodriguez Del Pino}, Bruno and {Venturi}, Giacomo}, title = {{A black hole in a near-pristine galaxy 700 million years after the Big Bang}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = may, eid = {arXiv:2505.22567}, pages = {arXiv:2505.22567}, doi = {10.48550/arXiv.2505.22567}, archiveprefix = {arXiv}, eprint = {2505.22567}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250522567M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, spectroscopy, theory}, month_numeric = {5} }

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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

arXiv e-prints, May 2025

Abs ADS arXiv

The advent of the James Webb Space Telescope has revolutionised our understanding of the high-redshift Universe, detecting bright, massive galaxies up to zrsim 10, and identifying 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 use a state-of-the- art zoom-in cosmological simulation of a quasar host to investigate whether these objects, during their assembly, can resemble any of the peculiar sources observed with JWST. 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, after a 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, carving 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{2025arXiv250505556Q, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = may, eid = {arXiv:2505.05556}, pages = {arXiv:2505.05556}, archiveprefix = {arXiv}, eprint = {2505.05556}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250505556Q}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, simulation}, 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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JWST/NIRSpec Observations of High Ionization Emission Lines in Galaxies at High Redshift

Mengtao Tang, Daniel P. Stark, Adèle Plat, and 7 more authors

arXiv e-prints, May 2025

Abs ADS arXiv

JWST spectroscopy has built large emission line samples at zrsim4, but it has yet to confidently reveal many galaxies with the hard radiation fields commonly associated with AGN photoionization. While this may indicate a weaker UV ionizing spectrum in many z>4 AGNs 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 NV\lambda1240 in two galaxies. One is a previously- confirmed z=6.98 Little Red Dot (LRD) with broad Hβ, and the other is a z=8.72 galaxy with a narrow line spectrum. Neither source exhibits CIV or HeII emission, indicating large NV/CIV and NV/HeII 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^+23.7_-10.4%) and UV-selected galaxies (2.2^+1.7_-1.0%) at z>4. The identification of narrow high ionization lines in the population of LRDs with strong Balmer absorption suggests the dense neutral hydrogen gas may not uniformly cover the nucleus. The NV/CIV and NV/HeII ratios suggest that efforts to identify high ionization lines should extend down in wavelength to the NV doublet.

@article{2025arXiv250506359T, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = may, eid = {arXiv:2505.06359}, pages = {arXiv:2505.06359}, archiveprefix = {arXiv}, eprint = {2505.06359}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250506359T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, non-agn, spectroscopy}, 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}, year = {2025}, month = may, volume = {984}, number = {2}, eid = {144}, pages = {144}, doi = {10.3847/1538-4357/adc727}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...984..144T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, non-agn, simulation, x-ray}, altmetric = {169068144}, eprint = {2410.03830}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {5} }

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A weak Lyα halo for an extremely bright Little Red Dot. Indications of enshrouded SMBH growth

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

arXiv e-prints, May 2025

Abs 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 unveiling 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_\rm H\sim10^24\,\rm cm^-2). We present a stringent test of such models using VLT/MUSE observations of A2744-45924, the most luminous LRD known to date (L_\rm Hα\approx10^44~\rm erg s^-1), located behind the Abell-2744 lensing cluster at z=4.464 (μ=1.8). We detect a moderately extended Lyα nebula (h\approx5.7 pkpc), spatially offset from the point-like Hα seen by JWST. The Lyα emission is narrow (\rm FWHM=270\pm 15~km s^-1), spatially offset to Hα, and faint (\rm Lyα=0.07Hα) compared to Lyα nebulae typically observed around quasars of similar luminosity. We detect compact N IV]λ1486 emission, spatially aligned with Hα, and a spatial shift in the far-UV continuum matching the Lyα offset. We discuss that Hα and Lyα have distinct physical origins: Hα originates from the AGN, while Lyα is powered by star formation. In the environment of A2744-45924, we identify four extended Lyα halos (Δz<0.02, Δr<100 pkpc). Their Lyα luminosities match expectations based on Hα emission, indicating no evidence for radiation from A2744-45924 affecting its surroundings. The lack of strong, compact, and broad Lyα and the absence of a luminous extended halo, suggest that the UV AGN light is obscured by dense gas cloaking the SMBH with covering factor close to unity.

@article{2025arXiv250509542T, 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$α$ halo for an extremely bright Little Red Dot. Indications of enshrouded SMBH growth}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = may, eid = {arXiv:2505.09542}, pages = {arXiv:2505.09542}, archiveprefix = {arXiv}, eprint = {2505.09542}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250509542T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, early universe, emission lines, spectroscopy}, 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 \rmμm 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 (\rm flux_W4 > 5  \rm mJy), optically faint (r > 23), or with red colour (r - W4 >8.38). Gemini/Gemini Near-InfraRed Spectrograph and Keck/Low-Resolution Imaging Spectrometer observations confirm 23 to be type 2 QSOs at z = 0.88 \!-\! 3.49. Multiband photometry is used for SED fitting, covering 0.1–10 μm in the rest frame. The IR emission is dominated by the dust torus, with an average luminosity of L_\rm torus = 10^46.84  \rm erg\,s^-1. 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 L_\rm bol = 10^46.28 \!-\! 10^48.08  \rm erg\,s^-1 and supermassive black hole masses of 10^8.18 \!-\! 10^9.98  \rm M_⊙, averaging L_\rm bol = 10^47.04  \rm erg s^-1 and M_\rm BH = 10^8.94  \rm M_⊙, 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 {\textendash} 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}, year = {2025}, month = may, volume = {539}, number = {2}, pages = {1562-1594}, doi = {10.1093/mnras/staf574}, 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}, altmetric = {176515277}, eprint = {2501.14026}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, 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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The Composite Spectrum of the Little Red Dots from an Inner Standard Disk and an Outer Gravitationally Unstable Disk

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

arXiv e-prints, May 2025

Abs ADS arXiv

One of the most mysterious results from observations of the James Webb Space Telescope (JWST) is the detection of numerous, high- redshift, very red, extremely compact, broad-line sources termed “little red dots” (LRDs). It is unclear whether the LRDs belong to an active galactic nucleus (AGN) or simply a collection of very compact star clusters. We build spectral energy distributions (SEDs) for 29 LRDs at z ≈3-8.5 based on JWST photometric and spectroscopic observations. We find that the V-shaped SEDs of these LRDs exhibit a roughly similar break frequency at ν_\rm b=10^14.96\pm0.06 Hz, which corresponds to λ_\rm b=3287_-424^+487 \textÅ in the rest frame. We propose that this unique SED can be explained by the combination of an inner standard disk and an outer gravitationally unstable accretion disk with Toomre parameter Q\sim1. The outer disk has a temperature of \sim2000-4000 K for typical AGN parameters, which can well reproduce the near- infrared to optical bump as observed in LRDs. This model can naturally explain the strong infrared to optical emission and the V-shaped SED with a similar break frequency ≃10^15 Hz for LRDs without invoking strong dust extinction or unusual stellar contribution from a host galaxy. Most LRDs stay in sub- Eddington state based on the SED modeling, which are intrinsically weak in X-rays.

@article{2025arXiv250512719Z, 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 the Little Red Dots from an Inner Standard Disk and an Outer Gravitationally Unstable Disk}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena}, year = {2025}, month = may, eid = {arXiv:2505.12719}, pages = {arXiv:2505.12719}, archiveprefix = {arXiv}, eprint = {2505.12719}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250512719Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, photometry, sed, theory}, month_numeric = {5} }

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

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

arXiv e-prints, May 2025

Abs ADS arXiv

We present a spectroscopic search for broad Hα emitters at z\raisebox-0.5ex\textasciitilde3.7-6.5 in the GOODS-N field, utilizing JWST/NIRCam slitless spectroscopy from FRESCO and CONGRESS, complemented by JADES imaging. We identify 19 broad Hα emitters with FWHM > 1000 km/s at z\raisebox-0.5ex\textasciitilde4-5.5, including 9 new sources. The black hole masses and AGN bolometric luminosities, inferred from the broad Hα components, indicate that most sources are accreting at \raisebox-0.5ex\textasciitilde10% of the Eddington limit. We derive their host stellar masses via 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 red slope. 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 Hα 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{2025arXiv250502895Z, 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$α$ Emitters in the GOODS-N Field Revealed by CONGRESS, FRESCO, and JADES}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = may, eid = {arXiv:2505.02895}, pages = {arXiv:2505.02895}, archiveprefix = {arXiv}, eprint = {2505.02895}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250502895Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, host galaxy, jwst, spectroscopy}, 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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NEXUS: A Spectroscopic Census of Broad-line AGNs and Little Red Dots at 3≲z≲6

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

arXiv e-prints, May 2025

Abs ADS arXiv

We present a spectroscopic sample of 23 broad-line AGNs (BLAGNs) at 3≲z≲6 selected using F322W2+F444W NIRCam/WFSS grism spectroscopy of the central 100 \rm 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 ∼10^-5\,\rm cMpc^-3, with a hint of declining towards the lower end of the probed redshift range. These BLAGNs and LRDs span broad Hα luminosities of ∼10^42.2-10^43.7\,\rm erg s^-1, black hole masses of ∼10^6.3-10^8.4 M_⊙, and Eddington ratios of ∼0.1-1 (median value 0.4), though the black hole mass and Eddington ratio estimates 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 parsec) 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. This host emission largely accounts for the peculiar UV upturn of the LRD spectral energy distribution. We also measure the small-scale (≲1\,\rm 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 3.30_-2.04^+2.88 and typical halo masses of a few \times 10^11 h^-1M_⊙for BLAGNs at the sample median redshift of z∼4.5. However, the inferred linear bias and halo masses of LRDs, while formally consistent with those for BLAGNs at ∼1.5σ, appear too large to be compatible with their space density, suggesting LRDs may have strong excess clustering on small scales.

@article{2025arXiv250520393Z, 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 $3\lesssim z\lesssim 6$}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = may, eid = {arXiv:2505.20393}, pages = {arXiv:2505.20393}, archiveprefix = {arXiv}, eprint = {2505.20393}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250520393Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, clustering, early universe, host galaxy, spectroscopy}, 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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Bridging Quasars and Little Red Dots: Insights into Broad-Line AGNs at z=5-8 from the First JWST COSMOS-3D Dataset

Xiaojing Lin, Xiaohui Fan, Feige Wang, and 30 more authors

arXiv e-prints, Apr 2025

Abs DOI ADS arXiv

We report the discovery of 13 broad-line AGNs at z = 5 - 8 from the first 10% data of the JWST Cycle 3 Treasury Program COSMOS-3D. These AGNs are identified by their broad Hα or Hβ emission lines through the NIRCam grism wide-field slitless spectroscopy. One object at z = 7.646 with broad Hβ 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 have reddened optical continua with slopes β_\rm opt>0. The remaining three objects have their overall SEDs that resemble those of UV-luminous quasars at similar redshifts, but their β_\rm opt, though negative, are not as blue as those of unobscured quasars. We also obtain MIRI photometry at 7.7-18 μm for two AGNs and place strong constraints on their rest- frame near-IR SED. 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 Hα luminosity functions (LFs) for the broad Hα emitters at z ≈5-6 and find a potential redshift evolution when compared with that of the z ≈4-5 sample. We also derive the Hβ LF at z\sim8 for AGNs and galaxies by combining our sample with those from the literature. The broad Hβ emitters in this work suggest a number density two 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{2025arXiv250408039L, 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 {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 AGNs at $z=5-8$ from the First JWST COSMOS-3D Dataset}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = apr, eid = {arXiv:2504.08039}, pages = {arXiv:2504.08039}, doi = {10.48550/arXiv.2504.08039}, archiveprefix = {arXiv}, eprint = {2504.08039}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250408039L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, sed, spectroscopy}, month_numeric = {4} }

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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

arXiv e-prints, Apr 2025

Abs DOI ADS arXiv

Little red dots (LRDs) are a population of red, compact objects discovered by JWST at z>4. At 44 to \sim10^-5.3\,\mathrmcMpc^-3 at 2.7<z<3.7 and \sim10^-5.7\,\mathrmcMpc^-3 at 1.7<z<2.7. We also present the Magellan/FIRE spectrum of our first followed-up candidate, DEEP23-z2LRD1 at z_\mathrmspec=2.26, as a proof of concept for our sample selection. Similar to high-redshift LRDs, the spectrum of DEEP23-z2LRD1 exhibits broad Hα emission with \mathrmFWHM\approx2400\,\mathrmkm s^-1 and with nearly symmetric narrow Hα absorption. Additionally, DEEP23-z2LRD1 has extremely narrow [OIII] lines with \mathrmFWHM\approx140\,\mathrmkm s^-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{2025arXiv250408032M, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Astrophysical Phenomena}, year = {2025}, month = apr, eid = {arXiv:2504.08032}, pages = {arXiv:2504.08032}, doi = {10.48550/arXiv.2504.08032}, archiveprefix = {arXiv}, eprint = {2504.08032}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250408032M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, non-jwst, photometry, sample selection, spectroscopy}, month_numeric = {4} }

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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

arXiv e-prints, Apr 2025

Abs DOI ADS arXiv

Galaxies grow alongside their central supermassive black holes (SMBHs), linked through fueling and feedback. However, the origins and details of this co-evolution remain unclear and differ significantly amongst modeling frameworks. Using a suite of semi-analytic models (SAMs), we trace SMBH mass assembly across M_\rm BH ∼10^6-10, \mathrmM_⊙. We find significant discrepancies between observations and physics-based models of the local black hole mass function (BHMF), likely due to differences in the underlying stellar mass function and the scaling relations therefrom used to infer the BHMF. However, most physics-based models agree at z ∼1-4 and align reasonably well with broad-line AGN BHMF from JWST observations at z=4-5. Most physics-based models reproduce the bolometric AGN luminosity evolution, except {\textbackslashsc Dark Sage}, which predicts an excess deviating from models and observations. Interestingly, this pronounced “knee’ in the bolometric AGN luminosity function predicted by {\textbackslashsc Dark Sage} around L_\rm bol ∼10^46  \mathrmerg \,s^-1 is consistent with the inferred luminosity of “Little Red Dots” at z=5-6, assuming that their entire emission originates from AGN activity. We analyze black hole mass build-up and accretion histories in {\textbackslashsc Dark Sage}, which, unlike other models, allows for super-Eddington accretion. We report that on average, SMBHs in {\textbackslashsc Dark Sage} primarily grow through secular disk instabilities and merger-driven cold gas accretion, while black hole mergers contribute 60\% of the total mass budget only for the most massive SMBHs by z=0.

@article{2025arXiv250411566P, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = apr, eid = {arXiv:2504.11566}, pages = {arXiv:2504.11566}, doi = {10.48550/arXiv.2504.11566}, archiveprefix = {arXiv}, eprint = {2504.11566}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250411566P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, month_numeric = {4} }

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Deciphering the Nature of Virgil: An Obscured AGN Lurking Within an Apparently Normal Lyman-\ensuremathα Emitter During Cosmic Reionization

Pierluigi Rinaldi, Pablo G. Pérez-González, George H. Rieke, and 46 more authors

arXiv e-prints, Apr 2025

Abs DOI ADS arXiv

We present a comprehensive analysis of the MIRI Extremely Red Object Virgil, a Lyman-α emitter at z_spec = 6.6379 \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\pm0.04 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 Hα, 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 μm 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 multi-wavelength approach incorporating MIRI to uncover such extreme sources at zrsim6 and to shed light on the interplay between galaxy evolution and early black hole growth during Cosmic Reionization.

@article{2025arXiv250401852R, 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 {Pei{\ss}ker}, 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 AGN Lurking Within an Apparently Normal Lyman-{\ensuremath{\alpha}} Emitter During Cosmic Reionization}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = apr, eid = {arXiv:2504.01852}, pages = {arXiv:2504.01852}, doi = {10.48550/arXiv.2504.01852}, archiveprefix = {arXiv}, eprint = {2504.01852}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250401852R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, sed, spectroscopy}, 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, photometry, sed, variability}, month_numeric = {4} }

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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

arXiv e-prints, Mar 2025

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.” Ubiquitous Balmer breaks suggest that they harbor old stellar populations in massive, compact host galaxies. We present ALMA observations of three LRDs at z=3.10, 4.46, and 7.04, targeting molecular and neutral gas via CO(7-6) and [CI](2-1), respectively. We do not detect CO in any target, placing conservative limits on the host molecular gas mass ≲1-5\times10^10 M_⊙. We report the tentative (4.9σ) detection of the [CI](2-1) line in A2744-45924 (z=4.46), one of the brightest known LRDs. The [CI] line is narrow (FWHM ∼80 km s^-1), implying a dynamical mass ≲10^10 M_⊙, adopting conservative limits for the galaxy size. The dynamical mass limit is significantly lower than expected from the local M_\rm BH-M_\rm dyn relation, and is an order of magnitude below the stellar mass derived from SED fitting, potentially supporting a non-stellar 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{2025arXiv250300998A, 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 = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, eid = {arXiv:2503.00998}, pages = {arXiv:2503.00998}, doi = {10.48550/arXiv.2503.00998}, archiveprefix = {arXiv}, eprint = {2503.00998}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250300998A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, non-agn, sed, spectroscopy}, month_numeric = {3} }

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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, host galaxy, jwst, sed}, altmetric = {177019079}, month_numeric = {3} }

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BlackTHUNDER strikes twice: rest-frame Balmer-line absorption and high Eddington accretion rate in a Little Red Dot at z=7.04

Francesco D’Eugenio, Roberto Maiolino, Michele Perna, and 28 more authors

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

JWST spectroscopy has revealed a population of compact objects at redshifts z=2-9 with ‘v’-shaped spectral energy distributions, broad permitted lines, and, often, hydrogen Balmer absorption. Among these ‘Little Red Dots’ (LRDs), Abell2744-QSO1 at z=7.04 has been confirmed to have time-variable equivalent width (EW) in its broad emission lines, confirming its AGN nature. We extend the analysis of NIRSpec/IFS data from the BlackTHUNDER survey to the Hαline. The broad-line profile in Abell2744-QSO1 is manifestly non-Gaussian, requiring at least two Gaussian components with full width at half maximum FWHM=450\pm50 and 1800\pm100 km s^-1. Crucially, we also detect a narrow-line Gaussian component, and strong Hαabsorption (EW relative to the continuum ≈30^+15_-9 A), confirming a connection between the strong Balmer break and line absorption. The absorber is at rest with respect to broad Hα, suggesting that the gas cannot be interpreted as an inflow or outflow, forming instead a long-lived structure. Its velocity dispersion is \sigma_abs = 100\pm10 km s^-1, consistent with the value inferred from the analysis of the Balmer break. Based on Hα, we infer a black hole mass of log(M_BH/M_⊙)=6.3-6.7, 0.9-1.3 dex smaller than previous estimates based on Hβ. The Eddington ratio is 0.7-1.6. Combining the high signal-to-noise ratio of the narrow Hαline with the spectral resolution R=3,700 of the G395H grating, we infer a narrow-line dispersion \sigma_n = 22^+5_-6 km s^-1, which places a stringent constraint on the black-hole-to-dynamical-mass ratio of this system to be M_BH/M_dyn>0.02-0.4. If M_BH is near the low-mass end of our estimates, the SMBH would be accreting at a super- Eddington rate. Alternatively, at the high-M_BH end, there would be minimal room for a host galaxy.

@article{2025arXiv250311752D, author = {{D'Eugenio}, Francesco and {Maiolino}, Roberto and {Perna}, Michele and {Uebler}, 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 and {Bunker}, Andrew J. and {Carniani}, Stefano and {Charlot}, St{\'e}phane and {Cresci}, Giovanni and {Curtis-Lake}, Emma and {Dalla Bont{\`a}}, Elena 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: rest-frame Balmer-line absorption and high Eddington accretion rate in a Little Red Dot at $z=7.04$}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, eid = {arXiv:2503.11752}, pages = {arXiv:2503.11752}, doi = {10.48550/arXiv.2503.11752}, archiveprefix = {arXiv}, eprint = {2503.11752}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250311752D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, month_numeric = {3} }

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

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

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

Recent James Webb Space Telescope (JWST) observations have revealed a population of sources with a compact morphology and a ‘v-shaped’ continuum, namely blue at rest-frame λ<4000A and red at longer wavelengths. The nature of these sources, called ‘little red dots’ (LRDs), is still debated, since it is unclear if they host active galactic nuclei (AGN) and their number seems to drastically drop at z<4. We utilise the 63 deg^2 covered by the quick Euclid Quick Data Release (Q1) to extend the search for LRDs to brighter magnitudes and to lower z than what has been possible with JWST to have a broader view of the evolution of this peculiar galaxy population. The selection is done by fitting the available photometric data (Euclid, Spitzer/IRAC, and ground-based griz data) with two power laws, to retrieve the rest-frame optical and UV slopes consistently over a large redshift range (i.e, z<7.6). We exclude extended objects and possible line emitters, and perform a visual inspection to remove imaging artefacts. The final selection includes 3341 LRD candidates from z=0.33 to z=3.6, with 29 detected in IRAC. Their rest-frame UV luminosity function, in contrast with previous JWST studies, shows that the number density of LRD candidates increases from high-z down to z=1.5-2.5 and decreases at even lower z. Less evolution is apparent focusing on the subsample of more robust LRD candidates having IRAC detections, 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. Follow-up studies of these LRD candidates are key to confirm their nature, probe their physical properties and check for their compatibility with JWST sources, since the different spatial resolution and wavelength coverage of Euclid and JWST could select different samples of compact sources.

@article{2025arXiv250315323E, 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). Extending the quest for little red dots to z<4}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, eid = {arXiv:2503.15323}, pages = {arXiv:2503.15323}, doi = {10.48550/arXiv.2503.15323}, archiveprefix = {arXiv}, eprint = {2503.15323}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250315323E}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {morphology, non-agn, photometry, sample selection, sed}, 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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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

arXiv e-prints, Mar 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 realistic sub-grid star formation efficiency (SFE) model, derived from AU-scale radiation-MHD simulations of molecular clouds with varying mass, density, and metallicity. Using this model for cloud-scale SFEs, the galaxy forms stars stochastically, assembling most of its 10^6~\rm M_⊙ in stars by redshift z=8 through two star-forming bursts (SFBs), each lasting \sim10~\rm Myr, separated by 80~\rm Myr of quiescence. Clouds reach SFEs up to 80% during the first SFB, forming bound star clusters (densities \sim10^2-4 ~\rm M_⊙\:pc^-2, radii ≲3~\rm pc) 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 Γ∼-0.4. The most massive star clusters (10^4-5 ~\rm M_⊙) grow through mergers and have metallicity spreads of 0.05 - 0.1 dex that roughly scale with mass. The second SFB forms loosely bound star clusters with higher metallicities: -1.95 < \log(Z/\rm Z_⊙) < -1.50 at lower SFEs (2 - 20%). At z ∼8.7, a nuclear star cluster (NSC) is seeded, growing 83% of its mass ( 2.4 \times 10^5 ~\rm M_⊙, 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 rsim 5.

@article{2025arXiv250308779G, 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 = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, eid = {arXiv:2503.08779}, pages = {arXiv:2503.08779}, doi = {10.48550/arXiv.2503.08779}, archiveprefix = {arXiv}, eprint = {2503.08779}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250308779G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, starburst}, month_numeric = {3} }

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Dot to dot: high-z little red dots in M_\rm bh-M_\rm ⋆ diagrams with galaxy-morphology-specific scaling relations and nuclear star clusters

Alister W. Graham, Igor V. Chilingarian, Dieu D. Nguyen, and 3 more authors

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

High-redshift little red dots (LRDs) detected with the James Webb Space Telescope are considered the cores of emerging galaxies. For the first time, we compare LRDs in M_\rm bh-M_⋆ diagrams with an array of z=0 galaxy-morphology-dependent scaling relations, along with the M_\rm bh-M_\rm ⋆,nsc relation for nuclear star clusters. The M_\rm bh-M_\rm ⋆,sph relations for spheroidal stellar systems are characterised by a nearly parallel set of quasi-quadratic (or steeper) distributions that are known to trace the ‘punctuated equilibrium’ of galaxies, reflecting their stepwise growth in black hole mass and merger-built bulge/spheroid mass. We show that LRDs are not equivalent to nuclear star clusters, with the latter having higher M_\rm bh/M_⋆ ratios. However, the least massive LRDs exhibit similar M_\rm bh and M_\rm ⋆,gal values as ultracompact dwarf (UCD) galaxies. We show that the LRDs span the M_\rm bh-M_\rm ⋆,gal diagram from UCD galaxies to primaeval lenticular galaxies. In contrast, spiral galaxies and the subset of major-merger-built early-type galaxies define offset relations. Additionally, we observe that low-z galaxies with active galactic nuclei align with the steep black hole scaling relations for disc galaxies defined by primarily inactive galaxies with directly measured black hole masses. Collectively, this highlights the benefits of considering galaxy morphology, which reflects their accretion and merger history, to understand the coevolution of galaxies and their black holes.

@article{2025arXiv250310958G, author = {{Graham}, Alister W. and {Chilingarian}, Igor V. and {Nguyen}, Dieu D. and {Soria}, Roberto and {Durre}, Mark and {Forbes}, Duncan A.}, title = {{Dot to dot: high-$z$ little red dots in $M\_{\rm bh}$-$M\_{\rm \star}$ diagrams with galaxy-morphology-specific scaling relations and nuclear star clusters}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, eid = {arXiv:2503.10958}, pages = {arXiv:2503.10958}, doi = {10.48550/arXiv.2503.10958}, archiveprefix = {arXiv}, eprint = {2503.10958}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250310958G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, morphology}, month_numeric = {3} }

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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

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

We present a statistical study on the formation and growth of black holes (BHs) seeded by gravothermal core-collapse of self- interacting dark matter (SIDM) halos at high redshifts, using a semi-analytical framework based on Monte-Carlo merger trees. We demonstrate that BH formation via gravothermal collapse naturally occurs in high-concentration halos at a characteristic mass scale determined by the SIDM cross section, and only during the early Universe. This mechanism is particularly promising for explaining the abundance of little red dots (LRDs) – a population of early, apparently galaxy-less active galactic nuclei hosting supermassive BHs. By incorporating this seeding process with simplified models of BH growth and mergers, we successfully reproduce the observed LRD mass function for moderately large cross sections of σ_0m ∼30 \mathrmcm^2 g^-1 and ω∼80\,\mathrmkm s^-1, intriguingly consistent with independent local constraints derived from galaxy rotation curves. Our results highlight the potential of high-redshift BH statistics as a complementary probe for constraining SIDM models.

@article{2025arXiv250323710J, 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 = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = mar, eid = {arXiv:2503.23710}, pages = {arXiv:2503.23710}, doi = {10.48550/arXiv.2503.23710}, archiveprefix = {arXiv}, eprint = {2503.23710}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250323710J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, non-agn, simulation, theory}, 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}, altmetric = {169163968}, lrdkeys = {dust, jwst, non-agn, 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 = {black hole mass, early universe, emission lines, spectroscopy, theory}, month_numeric = {3} }

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JWST’s little red dots: an emerging population of young, low-mass AGN cocooned in dense ionized gas

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

arXiv e-prints, Mar 2025

Abs DOI ADS arXiv

JWST has uncovered large numbers of compact galaxies at high redshift with broad hydrogen/helium lines. These include the enigmatic population known as “little red dots” (LRDs). Their nature is debated, but they are thought to be powered by supermassive black holes (SMBHs) or intense star formation. They exhibit unusual properties for SMBHs, such as black holes that are overmassive for their host galaxies and extremely weak X-ray and radio emission. Using the highest-quality JWST spectra, we show here that the lines are broadened by electron scattering with a narrow intrinsic line core. The data require high electron column densities and compact sizes (light days), which, when coupled with their high luminosities can only be explained by SMBH accretion. The narrow intrinsic cores of the lines imply upper limits on the black hole masses of 10^5-7 M_⊙, two orders of magnitude lower than previous estimates. These are among the lowest mass SMBHs known at high redshift and suggest that this is a population of young, rapidly growing SMBHs. They are enshrouded in a dense cocoon of ionized gas, probably related to their youth, from which they are accreting close to the Eddington limit. Reprocessed nebular emission from the dense cocoon dominates the optical spectrum, explaining most LRD spectral characteristics and helping to suppress radio and X-ray emission.

@article{2025arXiv250316595R, author = {{Rusakov}, V. and {Watson}, D. and {Nikopoulos}, G. P. and {Brammer}, G. and {Gottumukkala}, R. and {Harvey}, T. and {Heintz}, K. E. and {Nielsen}, R. D. 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 = {{JWST's little red dots: an emerging population of young, low-mass AGN cocooned in dense ionized gas}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = mar, eid = {arXiv:2503.16595}, pages = {arXiv:2503.16595}, doi = {10.48550/arXiv.2503.16595}, archiveprefix = {arXiv}, eprint = {2503.16595}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250316595R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, 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 = {black hole mass, early universe, 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}, altmetric = {166685969}, lrdkeys = {black hole mass, jwst, photometry, sed, simulation}, 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, starburst}, 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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High-velocity outflows in [OIII] emitters at z=2.5-9 from JWST NIRSpec medium-resolution spectroscopy

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

arXiv e-prints, Feb 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 (JADES). From a total sample of 1087 [OIII]5007 emitters we identify 40 galaxies with a blue-side broadened [OIII]5007 line at z=2.5-9. Of these, 34 are strong outflow candidates whilst 6 sources have broadening potentially driven by rotating clumps. Our outflow candidate sample is mainly composed of star-forming galaxies, including \raisebox-0.5ex\textasciitilde65% starbursts, which span the stellar mass range log10(M*/Msun)=7.5-11.0. It also includes two candidate type-2 active galactic nuclei (AGN) and a ’little red dot’ (LRD). We report a median outflow velocity of 531(+146)(-159) km/s 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(+0.36)(-0.32), 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* \raisebox-0.5ex~(10\^10)Msun, with most lowest stellar-mass M*<(10\^9)Msun galaxies reaching values well above unity, as is the case for local starburst galaxies.

@article{2025arXiv250218310C, 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 [OIII] emitters at z=2.5-9 from JWST NIRSpec medium-resolution spectroscopy}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = feb, eid = {arXiv:2502.18310}, pages = {arXiv:2502.18310}, doi = {10.48550/arXiv.2502.18310}, archiveprefix = {arXiv}, eprint = {2502.18310}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250218310C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, kinematics, 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 = {early universe, jwst, photometry, sed, spectroscopy}, 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 = {black hole mass, early universe, emission lines, jwst, theory}, 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 = {black hole mass, early universe, jwst, radio, x-ray}, 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}, altmetric = {175047560}, lrdkeys = {black hole mass, emission lines, jwst, 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}, altmetric = {165415691}, lrdkeys = {dust, early universe, jwst, sed, theory}, 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}, altmetric = {174962501}, lrdkeys = {dust, jwst, photometry, sed, 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, jwst, non-agn, 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}, altmetric = {160424236}, lrdkeys = {early universe, jwst, photometry, 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}, altmetric = {170113134}, lrdkeys = {black hole mass, dust, early universe, jwst, sed}, month_numeric = {1} }

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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

arXiv e-prints, Jan 2025

Abs DOI ADS arXiv

Recent observations from JWST have revealed an abundant population of active galactic nuclei (AGN) and so-called “Little Red Dots” (LRDs) at 2≲z ≲11, 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 z=7.04. The spectra confirm the presence of a smooth Balmer break and a broad Hβtracing the Broad Line Region (BLR) of an AGN. The small velocity dispersion of the Hβnarrow component indicates a small dynamical mass of the host galaxy of M_\rm dyn<4 \times 10^8~M_⊙, which implies that the stellar population cannot contribute more than 10% to the optical continuum. We show that the Balmer break can be well described by an AGN continuum absorbed by very dense (n_\rm H∼10^10~\rm cm^-3) 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 Hβabsorption, at a level consistent with a tentative detection (3σ) 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{2025arXiv250113082J, 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 {Arribas}, Santiago and {Bennett}, Jake S. and {Bunker}, Andrew and {Carniani}, Stefano 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 = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = jan, eid = {arXiv:2501.13082}, pages = {arXiv:2501.13082}, doi = {10.48550/arXiv.2501.13082}, archiveprefix = {arXiv}, eprint = {2501.13082}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250113082J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, spectroscopy}, 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}, altmetric = {172532541}, lrdkeys = {dust, early universe, jwst, photometry, 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}, altmetric = {171403980}, lrdkeys = {catalog, early universe, non-agn, radio, sample selection}, 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 = {kinematics, morphology, non-agn, non-jwst, 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 = {dust, early universe, jwst, 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}, altmetric = {173236030}, lrdkeys = {emission lines, jwst, kinematics, morphology, non-agn}, month_numeric = {12} }

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A Comprehensive Photometric Selection of ‘Little Red Dots’ in MIRI Fields: An IR-Bright LRD at z=3.1386 with Warm Dust Emission

Guillermo Barro, Pablo G. Perez-Gonzalez, Dale D. Kocevski, and 13 more authors

arXiv e-prints, Dec 2024

Abs DOI ADS arXiv

JWST has revealed a population of compact ‘Little Red Dots’ (LRDs) at zrsim4, 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-NIR colors enabling a more complete census of the population. This method identifies 248 LRDs with F444W6~\mum and peaks near \sim40~\mum, providing the first direct evidence of warm dust emission (T=50-100 K) in a LRD.

@article{2024arXiv241201887B, author = {{Barro}, Guillermo and {Perez-Gonzalez}, 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 IR-Bright LRD at $z=3.1386$ with Warm Dust Emission}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = dec, eid = {arXiv:2412.01887}, pages = {arXiv:2412.01887}, doi = {10.48550/arXiv.2412.01887}, archiveprefix = {arXiv}, eprint = {2412.01887}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241201887B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, photometry, sample selection, sed}, 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}, altmetric = {171422168}, lrdkeys = {dust, early universe, jwst, non-agn, starburst}, 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 = {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, host galaxy, kinematics, simulation}, 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

arXiv e-prints, Dec 2024

Abs DOI ADS arXiv

We present a detailed investigation into the abundance and morphology of high redshift quenched galaxies at 3 9.5) between 3 6.5) passive selections start to include examples of ’little red dots’ which complicates any conclusions until their nature is better understood.

@article{2024arXiv241211861R, author = {{Russell}, Tobias A. and {Dobric}, Neva and {Adams}, Nathan J. and {Conselice}, Christopher J. and {Austin}, Duncan and {Harvey}, Thomas and {Trussler}, James 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 = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = dec, eid = {arXiv:2412.11861}, pages = {arXiv:2412.11861}, doi = {10.48550/arXiv.2412.11861}, archiveprefix = {arXiv}, eprint = {2412.11861}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241211861R}, 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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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 = {clustering, emission lines, jwst, photometry, sed}, month_numeric = {12} }

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Red, hot, and very metal poor: extreme properties of a massive accreting black hole in the first 500 Myr

Roberta Tripodi, Nicholas Martis, Vladan Markov, and 29 more authors

arXiv e-prints, Dec 2024

Abs DOI ADS arXiv

The James Webb Space Telescope (JWST) has recently discovered a new population of objects at high redshift referred to as ‘Little Red Dots’ (LRDs). Their nature currently remains elusive, despite their surprisingly high inferred number densities. This emerging population of red point-like sources is reshaping our view of the early Universe and may shed light on the formation of high-redshift supermassive black holes. Here we present a spectroscopically confirmed LRD CANUCS-LRD-z8.6 at z_\rm spec=8.6319\pm 0.0005 hosting an Active Galactic Nucleus (AGN), using JWST data. This source shows the typical spectral shape of an LRD (blue UV and red optical continuum, unresolved in JWST imaging), along with broad Hβline emission, detection of high-ionization emission lines (CIV, NIV]) and very high electron temperature indicative of the presence of AGN. This is also combined with a very low metallicity (Z<0.1 Z_⊙). The presence of all these diverse features in one source makes CANUCS-LRD-z8.6 unique. We show that the inferred black hole mass of CANUCS-LRD-z8.6 (M_\rm BH=1.0^+0.6_-0.4\times 10^8\rm ~M_⊙) strongly challenges current standard theoretical models and simulations of black hole formation, and forces us to adopt ‘ad hoc’ prescriptions. Indeed if massive seeds, or light seeds with super-Eddington accretion, are considered, the observed BH mass of CANUCS-LRD-z8.6 at z=8.6 can be reproduced. Moreover, the black hole is over-massive compared to its host, relative to the local M_\rm BH-M_* relations, pointing towards an earlier and faster evolution of the black hole compared to its host galaxy.

@article{2024arXiv241204983T, 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 = {{Red, hot, and very metal poor: extreme properties of a massive accreting black hole in the first 500 Myr}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = dec, eid = {arXiv:2412.04983}, pages = {arXiv:2412.04983}, doi = {10.48550/arXiv.2412.04983}, archiveprefix = {arXiv}, eprint = {2412.04983}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241204983T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, 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 )\tex ttimes104 M _\ensuremath⊙, luminosities of LIR>=(8‑5+3)\texttimes 1010 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, 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}, altmetric = {161246260}, lrdkeys = {black hole mass, early universe, jwst, multi-wavelength, 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}, altmetric = {157269550}, lrdkeys = {dust, emission lines, host galaxy, jwst, 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 = {black hole mass, emission lines, host galaxy, jwst}, month_numeric = {11} }

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Exploring the Nature of Little Red Dots: Constraints on AGN and Stellar Contributions from PRIMER MIRI Imaging

Gene C. K. Leung, Steven L. Finkelstein, Pablo G. Pérez-González, and 20 more authors

arXiv e-prints, Nov 2024

Abs DOI ADS arXiv

JWST has revealed a large population of compact, red galaxies at z>4 known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 95 LRDs from the JWST PRIMER survey with complete photometric coverage from 1-18 \mum 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 \sim2 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 or galaxy dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.

@article{2024arXiv241112005L, 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 AGN and Stellar Contributions from PRIMER MIRI Imaging}}, journal = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = nov, eid = {arXiv:2411.12005}, pages = {arXiv:2411.12005}, doi = {10.48550/arXiv.2411.12005}, archiveprefix = {arXiv}, eprint = {2411.12005}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241112005L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, non-agn, photometry, sed}, 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, 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}, altmetric = {165611420}, lrdkeys = {early universe, jwst, sed, simulation, x-ray}, month_numeric = {11} }

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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

arXiv e-prints, Nov 2024

Abs DOI ADS arXiv

We analyze 99 photometrically selected Little Red Dots (LRDs) at z \raisebox-0.5ex~4-8 in the GOODS fields, leveraging ultra-deep JADES NIRCam short-wavelength (SW) data. We examine the morphology of 30 LRDs; the remaining 69 are predominantly compact, i.e. are strongly dominated by sources < 400 pc in diameter and lack extended components even in stacked SW band images. Among the LRDs selected for morphological analysis, 50% show at least two distinct, associated sources or galaxy components, while the others appear as single sources with highly asymmetric structures. We find median stellar masses of log10(M*/Msun) = 9.07(-0.08)(+0.11) for pure stellar models with Av \raisebox-0.5ex~1.16(+0.11)(-0.21) mag, and log10(M*/Msun) = 9.67(+0.17)(-0.27) for models including AGNs, where Av \raisebox-0.5ex~2.74(+0.55)(-0.71) mag, consistent with recent results showing LRDs tend to have high stellar masses and dust content when fitted with AGN models. NIRSpec spectra are available for 15 sources, 6 of which fall within the morphological analysis sample and show multiple components. Among these 15, broad H-alpha emission is detected in 40%, with full-width half- maximum (FWHM) ranging from 1200 to 2900 km/s. One source exhibits broad H-beta emission with FWHM = 2000 +/- 500 km/s. Analysis of line ratios probing the interstellar medium (ISM) reveals a composite nature, indicating AGN activity combined with stellar processes. These findings suggest LRDs have a mixed nature, with AGN signatures in some cases linked to disturbed morphologies observed at rest-frame UV wavelengths.

@article{2024arXiv241114383R, 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 {Hainline}, K. and {Helton}, J. M. and {Lin}, X. and {Lyu}, J. and {Johnson}, B. D. 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 = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = {2024}, month = nov, eid = {arXiv:2411.14383}, pages = {arXiv:2411.14383}, doi = {10.48550/arXiv.2411.14383}, archiveprefix = {arXiv}, eprint = {2411.14383}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241114383R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, host galaxy, jwst, morphology}, month_numeric = {11} }

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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

arXiv e-prints, Nov 2024

Abs DOI ADS arXiv

Among the most puzzling early discoveries of JWST are “Little Red Dots” – 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 Little Red Dots 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 (20/44, nearly all spatially unresolved) of extremely red Hαemitters at 2<z<6 exhibit a strong change in slope, and that all strong inflections appear associated with the Balmer limit (0.3645 \mum). Using a simple model of a reddened AGN with an unobscured scattered light component, we demonstrate that the observed “V shape” in Little Red Dots 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 evolved stellar populations in the rest-UV-to-optical, 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 Little Red Dot spectral energy distribution, the common inflection location suggests that it is most likely a single component that consistently dominates the rest-UV-to-optical in Little Red Dots, and that this component is associated with T\sim10^4 K hydrogen due to the clear preference for a break at H_∞.

@article{2024arXiv241103424S, 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 = {arXiv e-prints}, keywords = {Astrophysics - Astrophysics of Galaxies}, year = {2024}, month = nov, eid = {arXiv:2411.03424}, pages = {arXiv:2411.03424}, doi = {10.48550/arXiv.2411.03424}, archiveprefix = {arXiv}, eprint = {2411.03424}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv241103424S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, non-agn, sed, spectroscopy}, 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 = {black hole mass, early universe, jwst, sed, x-ray}, 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}, altmetric = {168749891}, lrdkeys = {black hole mass, dust, early universe, host galaxy, 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 = {jwst, multi-wavelength, photometry, sed, spectroscopy}, 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}, altmetric = {169948334}, lrdkeys = {dust, early universe, emission lines, 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 = {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}, altmetric = {166522152}, lrdkeys = {dust, 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 = {early universe, jwst, morphology, sed, 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 z=2.566, known to reside in a major-merger host galaxy. The rest-frame optical is best fit by a dust-reddened quasar (E(B - V)^\rm QSO= 1.55) with black-hole mass \rm log_10(Hβ, M\small BH [\rm M_⊙]) = 10.26 \pm 0.05, bolometric luminosity \rm L_Bol = \rm 10^48.16\,erg\, s^-1 and Eddington-scaled accretion rate log_10(\rm λ_Edd) = -0.19. 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 \rm km\,s^-1) 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 \dotε_k^ion = 10^44.61 \rm erg\,s^-1 ∼0.001\,L_Bol. 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}, altmetric = {166528538}, lrdkeys = {dust, emission lines, host galaxy, 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 = {Astrophysics - Instrumentation and Methods for Astrophysics, 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, starburst}, 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}, altmetric = {166591170}, lrdkeys = {catalog, early universe, jwst, morphology, starburst}, month_numeric = {8} }

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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.