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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.

2026

Little Red Dots as Late-stage Quasi-stars

Mitchell C. Begelman and Jason Dexter

The Astrophysical Journal, Jan 2026

Abs DOI ADS

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

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

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Rapid emergence of overmassive black holes in the early Universe

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

arXiv e-prints, Jan 2026

Abs ADS arXiv

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

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

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

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

Monthly Notices of the Royal Astronomical Society, Jan 2026

Abs DOI ADS

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

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

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

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

The Astrophysical Journal Letters, Jan 2026

Abs DOI ADS

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

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

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

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

Monthly Notices of the Royal Astronomical Society, Jan 2026

Abs DOI ADS

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

@article{2026MNRAS.545S2235J, author = {{Ji}, Xihan and {D'Eugenio}, Francesco and {Juod{\v{z}}balis}, Ignas and {Walton}, Dominic J. and {Fabian}, Andrew C. and {Maiolino}, Roberto and {Ramos Almeida}, Cristina and {Acosta Pulido}, Jose A. and {Belokurov}, Vasily A. and {Isobe}, Yuki and {Jones}, Gareth and {Maraston}, Claudia and {Scholtz}, Jan and {Simmonds}, Charlotte and {Tacchella}, Sandro and {Terlevich}, Elena and {Terlevich}, Roberto}, title = {{Lord of LRDs: insights into a 'Little Red Dot' with a low-ionization spectrum at z = 0.1}}, journal = {\mnras}, keywords = {galaxies: active, galaxies: dwarf}, year = {2026}, month = jan, volume = {545}, number = {3}, eid = {staf2235}, pages = {staf2235}, doi = {10.1093/mnras/staf2235}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026MNRAS.545S2235J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, local counterpart, spectroscopy, variability, x-ray}, month_numeric = {1} }

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

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

Monthly Notices of the Royal Astronomical Society, Jan 2026

Abs DOI ADS

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

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

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

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

The Astrophysical Journal, Jan 2026

Abs DOI ADS

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

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

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Do Little Red Dots Vary?

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

The Astrophysical Journal, Jan 2026

Abs DOI ADS

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

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

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

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

arXiv e-prints, Jan 2026

Abs ADS arXiv

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

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

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2025

The AGN nature of strong CIII emitters in the Early Universe with JWST

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

The semi-forbidden CIII] λλ1907,1909 doublet is a key tracer of high- ionization emission in the early universe. We present a study of CIII] emission in galaxies at z=5-7, using publicly available JWST/NIRSpec prism data from programs including CEERS, JADES, RUBIES and CAPERS. We built a sample of 61 CIII]-emitting galaxies, and we classified them as star-forming or active galactic nuclei (AGN) host galaxies using (1) rest-frame UV and optical emission-line diagnostic diagrams, and (2) the presence/absence of broad Balmer emission lines. The UV diagnostics are based on the combination of the rest-frame equivalent width (EW) of CIII] versus CIII]/HeII λ1640, and the EW of CIV versus CIV/HeII λ1640. For optical diagnostics, we employ the OHNO diagram, which combines [OIII] λ5007, Hβ, [NeIII] λ3869, and [OII] λλ3727,3729- and we find it has a low efficiency on separating AGN from SFG. We find that half of the sources in our sample (29 out of 61 galaxies) exhibit at least one secure indication of AGN activity while 13 are potential AGNs based on the CIII] diagnostic. Physical properties, including stellar mass and star formation rate, are derived through spectral energy distribution modeling with Bagpipes. Our analysis reveals that JWST is uncovering a population of strong CIII] emitters at high redshift (5<z<7) with a median EW of 22.8 A. This EW is higher than that of a control sample of CIII] emitters at redshift 3<z<4 with a median EW of 4.7 A. We find that for the same range of Muv, the CIII] EW increases by \sim0.67 dex from 3<z<4 to 5<z<7, indicating strong redshift evolution in the line’s strength. Finally, we identify five sources in our sample as Little Red Dots (LRDs); while four of these have already been identified as LRD in the literature, one is presented here for the first time.

@article{2025arXiv251216365A, author = {{Arevalo-Gonzalez}, F. and {Tripodi}, R. and {Llerena}, M. and {Pentericci}, L. and {Plat}, A. and {Barro}, G. and {Amor{\'\i}n}, R. O. and {Backhaus}, B. and {Calabr{\`o}}, A. and {Cleri}, N. J. and {Dickinson}, M. and {Dunlop}, J. S. and {Finkelstein}, S. L. and {Giavalisco}, M. and {Hirschmann}, M. and {Kartaltepe}, J. and {Koekemoer}, A. M. and {Lucas}, R. A. and {Napolitano}, L. and {Piconcelli}, E. and {Taylor}, A. J. and {Tombesi}, F. and {Trump}, J. R. and {Wang}, X.}, title = {{The AGN nature of strong CIII emitters in the Early Universe with JWST}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.16365}, pages = {arXiv:2512.16365}, archiveprefix = {arXiv}, eprint = {2512.16365}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251216365A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, sed}, month_numeric = {12} }

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

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

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

Guillermo Barro, Pablo G. Perez-Gonzalez, Dale Kocevski, and 19 more authors

arXiv e-prints, Dec 2025

Abs ADS arXiv

One of JWST’s most unexpected discoveries is the emergence of “Little Red Dots” (LRDs): compact sources at z rsim 3 with blue rest- frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest a population of early, unusual active galactic nuclei (AGNs). Using a comprehensive photometric selection and public NIRSpec/PRISM spectroscopy across six JWST deep fields, we identify a large sample of 118 LRDs with high-S/N spectra, enabling a population- wide analysis of their UV–optical continuum and emission lines. We find clear correlations between rest-frame color ([0.3-0.9 μm]) and slopes: bluer LRDs have blue UV slopes (β_ν,\mathrmUV ∼0.3) and red optical slopes, while redder LRDs exhibit redder UV slopes (β_ν,\mathrmUV ∼1.1). The continuum shape shows a similar trend: redder LRDs display prominent Balmer breaks and curvature, while bluer LRDs follow power-law-like optical SEDs. From literature compilations, \sim60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission-line diagnostics reveal a shift from high H_α/H_β and low [OIII]\lambda5007/H_β in redder LRDs to the opposite in bluer ones, along with stronger narrow-line equivalent widths, suggesting a transition from AGN- to host-dominated emission. We fit the spectra with a two-component model combining a gas-enshrouded black hole (BH) and a galaxy host. Redder LRDs require higher-luminosity, unreddened BHs and modestly reddened hosts; bluer LRDs require lower-luminosity, reddened BHs and dust-free galaxies. This framework reproduces the diversity in colors and spectral shape by varying BH luminosity, obscuration, and host-to-BH luminosity ratio.

@article{2025arXiv251215853B, author = {{Barro}, Guillermo and {Perez-Gonzalez}, Pablo G. and {Kocevski}, Dale and {Trump}, Jonathan R. and {Dickinson}, Mark and {Arrabal Haro}, Pablo and {Brooks}, Madisyn and {Finkelstein}, Steven L. and {Franco}, Maximilien and {Giavalisco}, Mauro and {Grogin}, Norman A. and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Larson}, Rebecca L. and {Leung}, Gene C. K. and {Lucas}, Ray A. and {McGrath}, Elizabeth J. and {Papovich}, Casey and {Perez-Diaz}, Borja and {Taylor}, Elizabeth and {Tripodi}, Roberta and {Yung}, L. Y. Aaron}, title = {{From ``The Cliff'' to ``Virgil'': Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.15853}, pages = {arXiv:2512.15853}, archiveprefix = {arXiv}, eprint = {2512.15853}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251215853B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, host galaxy, jwst, sed, spectroscopy}, month_numeric = {12} }

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HELM’s deep: Highly Extincted Low-Mass galaxies seen by JWST

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

@article{2025arXiv251214822B, author = {{Bisigello}, L. and {Gandolfi}, G. and {Grazian}, A. and {Rodighiero}, G. and {Girardi}, G. and {Renzini}, A. and {Vietri}, A. and {McGrath}, E. and {Holwerda}, B. and {Abdurro'uf} and {Castellano}, M. and {Giulietti}, M. and {Gruppioni}, C. and {Hathi}, N. and {Koekemoer}, A. M. and {Lucas}, R. and {Pacucci}, F. and {P{\'e}rez-Gonz{\'a}lez}, P. G. and {Yung}, L. Y. A. and {Arrabal Haro}, P. and {Backhaus}, B. E. and {Bagley}, M. and {Dickinson}, M. and {Finkelstein}, S. and {Kartaltepe}, J. and {Kirkpatrick}, A. and {Papovich}, C. and {Pirzkal}, N.}, title = {{HELM's deep: Highly Extincted Low-Mass galaxies seen by JWST}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.14822}, pages = {arXiv:2512.14822}, archiveprefix = {arXiv}, eprint = {2512.14822}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251214822B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {clustering, dust, jwst, morphology, sed}, month_numeric = {12} }

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

@article{2025arXiv251217997C, author = {{Cantiello}, Matteo and {Hassan}, Jake B. and {Perna}, Rosalba and {Armitage}, Philip J. and {Begelman}, Mitchell C. and {Jiang}, Yan-Fei and {Ryu}, Taeho and {Townsend}, Richard H. D.}, title = {{Pulsational Instability of Quasi-Stars: Interpreting the Variability of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Astrophysics of Galaxies, Solar and Stellar Astrophysics}, year = {2025}, month = dec, eid = {arXiv:2512.17997}, pages = {arXiv:2512.17997}, archiveprefix = {arXiv}, eprint = {2512.17997}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251217997C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, theory, variability}, month_numeric = {12} }

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Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots

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

Monthly Notices of the Royal Astronomical Society, Dec 2025

Abs DOI ADS arXiv

Little Red Dots (LRDs) are compact sources at z > 5 discovered through JWST spectroscopy. Their spectra exhibit broad Balmer emission lines (), alongside absorption features and a pronounced Balmer break - evidence for a dense, neutral hydrogen medium, in which the n = 2 state is significantly populated. 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, we examine their imprint on line shapes and ratios. Resonance scattering produces strong deviations from Case B flux ratios, clear differences between H\ensuremathα and H\ensuremathβ, and encodes gas kinematics in line profiles but cannot broaden H\ensuremathβ due to conversion to Pa\ensuremathα. While Raman scattering can yield broad wings, scattering of the UV continuum is disfavored given the absence of strong FWHM variations across transitions. Raman scattering of higher Lyman-series emission can produce H\ensuremathα/H\ensuremathβ wing width ratios of \ensuremath≳ 1.28, agreeing with observations. Thomson scattering can reproduce the observed wings under plausible conditions - e.g., T_e \raisebox-0.5ex~10^4 K and - and lead to black hole mass overestimates by factors \ensuremath≳ 10. Our results provide a framework for interpreting hydrogen lines in LRDs and similar systems.

@article{2025MNRAS.tmp.2008C, author = {{Chang}, Seok-Jun and {Gronke}, Max and {Matthee}, Jorryt and {Mason}, Charlotte}, title = {{Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots}}, journal = {\mnras}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, doi = {10.1093/mnras/staf2131}, archiveprefix = {arXiv}, eprint = {2508.08768}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.tmp.2008C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, simulation, spectroscopy}, month_numeric = {12} }

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Dust Budget Crisis in Little Red Dots

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

The Astrophysical Journal Letters, Dec 2025

Abs DOI ADS

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

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

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A cosmologist’s take on Little Red Dots

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

@article{2025arXiv251219666D, author = {{De Luca}, Valerio and {Del Grosso}, Loris and {Franciolini}, Gabriele and {Kritos}, Konstantinos and {Berti}, Emanuele and {D'Orazio}, Daniel and {Silk}, Joseph}, title = {{A cosmologist's take on 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 = dec, eid = {arXiv:2512.19666}, pages = {arXiv:2512.19666}, archiveprefix = {arXiv}, eprint = {2512.19666}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251219666D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, theory}, month_numeric = {12} }

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

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

Astronomy & Astrophysics, Dec 2025

Abs DOI ADS

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

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

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On the Fate of Little Red Dots

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

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

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

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

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Discovery of two little red dots transitioning into quasars

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

James Webb Space Telescope (JWST) has uncovered a new population of compact objects that show a unique V-shaped spectral energy distribution (SED) in the UV and optical wavelength range. These so-called “little red dots” (LRDs) often exhibit broad Balmer emission lines, indicative of the presence of active galactic nuclei (AGNs). They generally lack detection of X-ray, radio, and mid-IR radiation, which is fundamentally different from typical AGNs. Various models, including super-Eddington- accreting black holes enshrouded in dense and dust-poor gas, have been proposed to explain these features. However, the nature of LRDs remains debated, and their evolutionary fate is unclear. Here we report two unusual LRDs at redshift z = 2.868 and 2.925 that are in a transitional phase towards typical AGNs. Their V-shaped SEDs, compact optical morphology, and broad emission lines satisfy the defining criteria of LRDs. On the other hand, they exhibit intense X-ray, radio, and mid-IR radiation that is much stronger than previously known LRDs. These hybrid properties suggest that the dense gas envelope around their central black holes is dispersing, allowing high- energy photons and radio emission to escape. Meanwhile, a dust torus is forming. This finding provides a direct insight into the nature of LRDs and indicates that at least some LRDs will evolve into AGNs or quasars at later times.

@article{2025arXiv251202096F, author = {{Fu}, Shuqi and {Zhang}, Zijian and {Jiang}, Danyang and {Chen}, Jie and {Jiang}, Linhua and {Ho}, Luis C. and {Inayoshi}, Kohei and {Chen}, Kaiyuan and {Lyu}, Jianwei and {Sun}, Fengwu and {Wang}, Feige and {Yang}, Jinyi}, title = {{Discovery of two little red dots transitioning into quasars}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.02096}, pages = {arXiv:2512.02096}, archiveprefix = {arXiv}, eprint = {2512.02096}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251202096F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, radio, sed, x-ray}, month_numeric = {12} }

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VENUS: When Red meets Blue – A multiply imaged Little Red Dot with an apparent blue companion behind the galaxy cluster Abell 383

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

We report the discovery of a doubly-imaged Little Red Dot (LRD) candidate behind the galaxy cluster Abell 383, which we dub A383-LRD1. Initially classified as a dropout galaxy in HST imaging with several ground-based emission line detections placing it at z_\mathrmspec=6.027, new JWST/NIRCam observations taken as part of the cycle 4 VENUS survey now reveal that the source consists of two underlying components: A red point-source with a V-shaped SED consistent with LRD selection criteria, and a nearby (∼380 pc) compact blue companion which was the main contributor to the previous rest- frame UV detections. Based on lensing symmetry and its SED, the LRD appears to lie at a similar redshift as well. The magnification of the two images of A383-LRD1 is μ_\mathrmA=16.2\pm1.2 and μ_\mathrmB=9.0\pm0.6, respectively, and the predicted time delay between them is Δt_\mathrmgrav=5.20\pm0.14 yr (\sim0.7 yr in the rest- frame). After correcting for the lensing magnification, we derive an absolute magnitude of M_\mathrmUV,LRD=-16.8\pm 0.3 for the LRD, and M_\mathrmUV,BC=-18.2\pm 0.2 for the blue companion. We perform SED fits to both components, revealing the LRD to be best fitted with a black hole star (BH*) model and a substantial host galaxy, and the blue companion with an extremely young, emission-line dominated star-forming nebula. A383-LRD1 represents the second known multiply-imaged LRD detected to date, following A2744-QSO1, and to our knowledge, the first LRD system with a confirmed detection of [C _II]\lambda158 μm emission from ALMA observations. Thanks to lensing magnification, this system opens a unique door to study the relation between a LRD, its host galaxy, and its environment, and represents a prime candidate for deep JWST spectroscopy and high-resolution ALMA follow-up observations.

@article{2025arXiv251202117G, author = {{Golubchik}, Miriam and {Furtak}, Lukas J. and {Allingham}, Joseph F. V. and {Zitrin}, Adi and {Akins}, Hollis B. and {Kokorev}, Vasily and {Fujimoto}, Seiji and {Abdurro'uf} and {Amor{\'\i}n}, Ricardo O. and {Bauer}, Franz E. and {Bezanson}, Rachel and {Brada{\v{c}}}, Marusa and {Bradley}, Larry D. and {Brammer}, Gabriel B. and {Chisholm}, John and {Coe}, Dan and {Conselice}, Christopher J. and {Dayal}, Pratika and {Dessauges-Zavadsky}, Miroslava and {Diego}, Jose M. and {Faisst}, Andreas L. and {Fei}, Qinyue and {Ferguson}, Henry C. and {Finkelstein}, Steven L. and {Frye}, Brenda L. and {Gonz{\'a}lez-Otero}, Mauro and {Greene}, Jenny E. and {Harikane}, Yuichi and {Hsiao}, Tiger Yu-Yang and {Inayoshi}, Kohei and {Jim{\'e}nez-Teja}, Yolanda and {Knudsen}, Kirsten and {Koekemoer}, Anton M. and {Labb{\'e}}, Ivo and {Lucas}, Ray A. and {Magdis}, Georgios E. and {Matthee}, Jorryt and {Messa}, Matteo and {Naidu}, Rohan P. and {Nakane}, Minami and {Noirot}, Ga{\"e}l and {Pan}, Richard and {Papovich}, Casey and {Richard}, Johan and {Ricotti}, Massimo and {Robbins}, Luke and {Stark}, Daniel P. and {Sun}, Fengwu and {Treu}, Tommaso and {Tripodi}, Roberta and {Vanzella}, Eros and {Willott}, Chris and {Windhorst}, Rogier A.}, title = {{VENUS: When Red meets Blue -- A multiply imaged Little Red Dot with an apparent blue companion behind the galaxy cluster Abell 383}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.02117}, pages = {arXiv:2512.02117}, archiveprefix = {arXiv}, eprint = {2512.02117}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251202117G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, host galaxy, jwst, sed, spectroscopy}, month_numeric = {12} }

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

Carl Audric Guia and Fabio Pacucci

Research Notes of the American Astronomical Society, Dec 2025

Abs DOI ADS

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

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

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

Kohei Inayoshi and Luis C. Ho

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

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

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

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

Monthly Notices of the Royal Astronomical Society, Dec 2025

Abs DOI ADS arXiv

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

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

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

We present a cosmological zoom-in simulation targeting the high redshift compact progenitor phase of massive galaxies, with the most massive galaxy reaching a stellar mass of M_⋆=8.5\times 10^10 M_⊙ at z=5. The dynamics of supermassive black holes (SMBHs) is modelled from seeding down to their coalescence at sub-parsec scales due to gravitational wave (GW) emission by utilising a new version of the KETJU code, which combines regularised integration of sufficiently massive SMBHs with a dynamical friction subgrid model for lower-mass SMBHs. All nine massive galaxies included in this study go through a gas-dominated phase of early compaction in the redshift range of z∼7-9, starting at stellar masses of M_\starrsim 10^8 \mathrmM_⊙and ending at a few times M_⋆∼10^9 \mathrmM_⊙. The sizes, masses and broad band fluxes of these compact systems are in general agreement with the population of systems observed with JWST known as ‘Little Red Dots’. In the compact phase, the stellar and SMBH masses grow rapidly, leading to a sharp decline in the central gas fractions. The outer regions, however, remain relatively gas- rich, leading to subsequent off-centre star formation and size growth. Due to the very high central stellar densities (ρ_⋆rsim 10^13\,\mathrmM_⊙/kpc^3), the SMBHs merge rapidly, typically just ∼4-35 \mathrmMyr after the SMBH binaries have become bound. Combining KETJU with the phenomenological PhenomD model resolves the complete evolution of the GW emission from SMBH binaries through the Pulsar Timing Array frequency waveband up to the final few orbits that produce GWs observable with the future LISA mission.

@article{2025arXiv251211665K, author = {{Keitaanranta}, Atte and {Johansson}, Peter H. and {Rawlings}, Alexander and {Tuominen}, Toni and {Rantala}, Antti and {Naab}, Thorsten and {Liao}, Shihong and {Reinoso}, Basti{\'a}n}, title = {{Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.11665}, pages = {arXiv:2512.11665}, archiveprefix = {arXiv}, eprint = {2512.11665}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251211665K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, simulation}, month_numeric = {12} }

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Black hole envelopes in Little Red Dots

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

Monthly Notices of the Royal Astronomical Society, Dec 2025

Abs DOI ADS

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

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

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

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

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

Mitsuru Kokubo and Yuichi Harikane

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

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

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

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X-ray properties of massive compact relic galaxies

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

Astronomy & Astrophysics, Dec 2025

Abs DOI ADS

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

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

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

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

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COSMOS-3D: Two obscured X-ray AGNs with hot dust and He Iλ10830 absorption at z\raisebox-0.5ex\textasciitilde3

Zi-Jian Li, Siwei Zou, Jianwei Lyu, and 24 more authors

arXiv e-prints, Dec 2025

Abs ADS arXiv

We report the discovery of two broad-line X-ray AGNs cid_414 and cid_947 at z\raisebox-0.5ex\textasciitilde3 that exhibit prominent He Iλ10830+ Paγ emission and absorption, identified from the JWST Cycle 3 large GO treasury program COSMOS-3D using NIRCam F444W grism spectroscopy. Additional UV/optical line measurements (e.g., Lyα, Si IV, C IV) come from complementary COSMOS-field spectroscopy. Both sources are robustly detected in the mid-infrared, with detections in MIRI F1000W for both AGNs and an additional detection in MIRI F2100W for cid_414, indicating the presence of hot dust emission. The source cid_947 shows a higher He Iλ10830 absorption column density and X-ray-inferred N_\rm H, and displays strong outflow signatures in He I, Si IV, and C IV with velocity offsets exceeding 5000 km/s. The source cid_414 shows a narrow Lyα emission line with luminosity \log L_\rm Lyα=42.49\pm0.01~\mathrmerg~s^-1 and a higher intrinsic 2-10 keV X-ray luminosity. Host-galaxy decomposition and multi- component SED fitting indicate that cid_947 hosts a more massive black hole but lower star formation rate than cid_414. From simplified photoionization modeling, we infer that the dense absorbing gas has a characteristic size comparable to the nuclear broad-line region and is likely kinematically coupled to the obscuration associated with the dust torus. He Iλ1083 absorption has also been identified in several compact little red dots at similar redshifts. Together with the two AGNs reported here, these findings suggest that dense circumnuclear gas are plausibly prevalent at high redshift and plays an important role in regulating AGN obscuration and black hole– host co-evolution.

@article{2025arXiv251202093L, author = {{Li}, Zi-Jian and {Zou}, Siwei and {Lyu}, Jianwei and {Champagne}, Jaclyn B. and {Huang}, Jia-Sheng and {Cheng}, Cheng and {Fu}, Shuqi and {Zhang}, Zijian and {Jiang}, Danyang and {Lee}, Khee-Gan and {Wang}, Feige and {Fan}, Xiaohui and {Yang}, Jinyi and {Li}, Ruancun and {Akins}, Hollis B. and {Bian}, Fuyan and {Faisst}, Andreas L. and {Ho}, Luis C. and {Inayoshi}, Kohei and {Jiang}, Linhua and {Jin}, Xiangyu and {Kakiichi}, Koki and {Kartaltepe}, Jeyhan S. and {Li}, Zihao and {Liu}, Weizhe and {Schindler}, Jan-Torge and {Tee}, Wei Leong}, title = {{COSMOS-3D: Two obscured X-ray AGNs with hot dust and He I$λ$10830 absorption at z\raisebox{-0.5ex}\textasciitilde3}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.02093}, pages = {arXiv:2512.02093}, archiveprefix = {arXiv}, eprint = {2512.02093}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251202093L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, spectroscopy, x-ray}, month_numeric = {12} }

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

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

Astronomy & Astrophysics, Dec 2025

Abs DOI ADS

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

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

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

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

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Radio Detection of a Local Little Red Dot

L. F. Rodriguez and I. F. Mirabel

arXiv e-prints, Dec 2025

Abs ADS arXiv

Context. One of the most important discoveries by the James Webb Space Telescope (JWST) is the unexpected existence in the Early Universe (z > 4) of very large quantities of “Little Red Dots” (LRDs), compact luminous red galaxies of intriguing physical properties. Aims. We wish to know if LRDs may host accreting Intermediate/Supermassive Black Holes (IMBHs/SMBHs) that may power LRDs, and compare them with the effect of clusters of massive stars. The spectrum of radio emission (synchrotron vs thermal) can be used to know which between these two types of energy sources is the dominant one. Methods. So far LRDs at high redshifts have not been detected at radio wavelengths and it is not known why. Assuming this could be due to their large distances and/or present limitations of observational capabilities, we analyze here archive Very Large Array radio observations of two analog candidates of LRDs in the Local Universe (LLRDs) at redshifts z = 0.1 - 0.2. Results. The LLRD source J1047+0739 at z = 0.1682 is detected at 6.0 GHz in 2018 with the VLA-A of NRAO as a compact source with radii less than 0.2 arc sec (< 600 pc at d = 700 Mpc). Its flux density was 117\pm8 μJy and its spectral index was -0.85, which is typical of optically-thin synchrotron emission. It is also detected at 5.0 GHz in 2010 with the VLA-C, showing a flux density of 43\pm3 μJy. Conclusions. The observed flux densities can be provided by a radio luminous supernova. The increase in flux density over eight years can be explained as the result of two independent supernovae or as the radio re- brightening of a single one. Radio time monitoring of this and other LLRDs could help clarify the mystery of the radio silence of its cosmological counterparts.

@article{2025arXiv251203331R, author = {{Rodriguez}, L. F. and {Mirabel}, I. F.}, title = {{Radio Detection of a Local Little Red Dot}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.03331}, pages = {arXiv:2512.03331}, archiveprefix = {arXiv}, eprint = {2512.03331}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251203331R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, local counterpart, non-agn, radio, variability}, month_numeric = {12} }

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

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

Monthly Notices of the Royal Astronomical Society, Dec 2025

Abs DOI ADS arXiv

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

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

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

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

The Astrophysical Journal, Dec 2025

Abs DOI ADS

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

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

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

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

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

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

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

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

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

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

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

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

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

Little red dots (LRDs) newly discovered with JWST are active galactic nuclei (AGN) that may represent black hole (BH) growth at the earliest cosmic epochs. These sources show puzzling features unlike typical AGNs, including red optical continua, weak hot- dust emission, and a lack of detectable X-rays. Previously, LRDs have often been interpreted as dust-reddened AGNs, leading to severe inconsistencies with the luminosity and BH mass densities inferred for previously known AGNs over 0<z<5. The BH-envelope (BHE) model has been proposed to explain these characteristics, in which an accreting BH is enshrouded by a dense, optically thick gaseous envelope. In this Letter, we reanalyze the SEDs of ∼400 photometric LRDs in the COSMOS-Web survey using the BHE model and reassess their implications for cosmological BH evolution. We find that the optical-NIR spectra of LRDs are well reproduced by blackbody emission with an effective temperatures of 4000-6000~\K. Within the BHE framework, the inferred bolometric luminosities decrease by rsim1-2 orders of magnitude compared to dust-reddened AGN assumptions. As a result, the revised luminosity function, BH accretion density, and BH mass function become consistent with those of AGNs at z<5. The stellar masses of LRD hosts are estimated by attributing the UV excesses to star formation. Although the resulting M_\rm BH/M_⋆ratio remains higher than the local empirical value, the excess is modest. Overall, the BHE model not only resolves the spectral features of LRDs but also brings their statistical properties into agreement with the broader cosmological BH population.

@article{2025arXiv251204208U, author = {{Umeda}, Hiroya and {Inayoshi}, Kohei and {Harikane}, Yuichi and {Murase}, Kohta}, title = {{A Black-Hole Envelope Interpretation for Cosmological Demographics of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.04208}, pages = {arXiv:2512.04208}, archiveprefix = {arXiv}, eprint = {2512.04208}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251204208U}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, sed}, month_numeric = {12} }

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Little Red Dots: The Assembly of Early Supermassive Black Holes in the JWST Era

David D Vaida and Ryan Jeffrey Farber

arXiv e-prints, Dec 2025

Abs ADS arXiv

Since the launch of James Webb Space Telescope (JWST) in late 2021, our understanding of high-redshift objects has faced several upheavals. JWST has discovered much more massive galaxies and supermassive black holes (SMBH) than cosmological models had expected. Furthermore, JWST observations have revealed an entirely novel population of high-redshift objects. Characterized by a dominant red rest-frame component and point- like morphology, these “little red dots” (LRD) have set off a flurry of observational and theoretical follow-up. The current identity of LRD is highly debated, yet falling into two main scenarios: active galactic nuclei (i.e., SMBH) or compact star- forming regions. If star-forming, LRD would represent the highest stellar densities ever observed. If SMBH, their high Eddington fractions, and already high masses, help elucidate the growth of the most massive SMBH found by JWST in the early Universe (z rsim4). In this mini-review, we present the observational evidence accumulated to date, including sub- millimeter probes of LRD dust masses, constraints on radio and X-ray emission from stacking, and rest-frame ultraviolet optical measurements provided by JWST. Furthermore, we highlight how identifying additional LRD that are truly primarily SMBH- driven may help to shed light on the formation of ‘overly massive’ SMBH discovered by JWST within the first billion years since the Big Bang.

@article{2026arXiv260100089V, author = {{Vaida}, David D and {Farber}, Ryan Jeffrey}, title = {{Little Red Dots: The Assembly of Early Supermassive Black Holes in the JWST Era}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = dec, eid = {arXiv:2601.00089}, pages = {arXiv:2601.00089}, archiveprefix = {arXiv}, eprint = {2601.00089}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260100089V}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, multi-wavelength, sed}, month_numeric = {12} }

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Black hole stars really do exist

Alex Wilkins

New Scientist, Dec 2025

Abs DOI ADS

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

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

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

Tak-Pong Woo

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

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

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

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

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

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Balmer Transition Signatures from Gas-Enshrouded, Dust-Poor Active Galactic Nuclei

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

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

@article{2025arXiv251211050Y, author = {{Yan}, Zu and {Inayoshi}, Kohei and {Chen}, Kejian and {Guo}, Jingsong}, title = {{Balmer Transition Signatures from Gas-Enshrouded, Dust-Poor Active Galactic Nuclei}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = dec, eid = {arXiv:2512.11050}, pages = {arXiv:2512.11050}, archiveprefix = {arXiv}, eprint = {2512.11050}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251211050Y}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, spectroscopy, theory}, month_numeric = {12} }

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

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

The Astrophysical Journal, Dec 2025

Abs DOI ADS arXiv

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

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

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Primordial Black Holes as Seeds for Extremely Overmassive AGN Observed by JWST

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

arXiv e-prints, Dec 2025

Abs ADS arXiv

The James Webb Space Telescope (JWST) has recently identified Abell 2744-QSO1 as a compact, metal-poor, black hole (BH) dominated galaxy at z≃7. This system exhibits an extreme black- hole-to-stellar mass ratio and unusually low metallicity, posing significant challenges to BH seeding models. Motivated by these discoveries, we perform high-resolution cosmological simulations with a massive primordial black hole (PBH; M_\rm BH=5\times10^7 M_⊙) seed, incorporating for the first time a fully coupled treatment of PBH accretion, BH feedback, and Population\raisebox-0.5ex\textasciitildeIII/II star formation and stellar feedback. Although PBHs accelerate structure formation through the seed effect, the associated strong thermal feedback from the accretion delays the onset of star formation to z≲10, producing short, bursty episodes throughout the subsequent evolution. PBH-driven outflows expel enriched gas from the nucleus, while sustained inflows from the intergalactic medium continuously replenish pristine material. This feedback-regulated cycle naturally yields low accretion rates (\dotm_\rm BH/\dotm_\rm edd ∼1-10%), subsolar metallicities (Z/Z_⊙\lesssim10^-2) and extreme M_\rm BH/M_⋆ratios during both the initial star-forming phase and the subsequent quenching phases, in excellent agreement with JWST observations. Our results demonstrate that massive PBHs offer a viable pathway for forming the most extreme high-redshift systems, providing a physically motivated explanation for the extraordinary properties of Abell 2744-QSO1, as a sub-class of the broader population of JWST-discovered “little red dots”.

@article{2025arXiv251214066Z, author = {{Zhang}, Saiyang and {Liu}, Boyuan and {Bromm}, Volker and {K{\"u}hnel}, Florian}, title = {{Primordial Black Holes as Seeds for Extremely Overmassive AGN Observed by JWST}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = dec, eid = {arXiv:2512.14066}, pages = {arXiv:2512.14066}, archiveprefix = {arXiv}, eprint = {2512.14066}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251214066Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, simulation}, month_numeric = {12} }

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

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

arXiv e-prints, Dec 2025

Abs DOI ADS arXiv

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

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

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

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

Monthly Notices of the Royal Astronomical Society, Nov 2025

Abs DOI ADS

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

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

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

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

arXiv e-prints, Nov 2025

Abs ADS arXiv

Several local (z≲0.2) metal-poor dwarf AGNs have remarkably similar properties to those of high-redshift Little Red Dots (LRDs), and are recently proposed to be local analogs of LRDs. We use long-term photometric and spectroscopic observations of three local LRDs spanning ∼20 years to measure variability in their rest-frame optical continuum and broad Hα emission lines. Using ZTF light curves over a rest-frame ∼5 yr baseline, the r-band intrinsic rms variability is (9\times 10^-5)_\rm -9E-5^+0.014 mag (J1022), 0.025\pm0.004 mag (J1025) and 0.020\pm0.005 mag (J1047), indicating low intrinsic variability (<3-4% at 3σ). These rms variability amplitudes are much lower than those for dwarf AGNs and more massive quasars. There is little structure in the optical variability structure functions for the three local LRDs, in contrast to normal AGN variability. Using available multi-epoch spectra, we constrain the broad Hα line flux variability to be less than a few percent, without significant profile changes, over a rest-frame baseline of ∼15 yrs in J1025 and J1047, respectively. The three LRDs stand out in the Balmer line properties compared with normal broad-line AGNs, with exceptionally large Hα equivalent widths and Hα/Hβ ratios far exceeding the Case B recombination value. In the context of recent theoretical models of LRDs as dense gas-enshrouded massive black holes with super-Eddington accretion, our results suggest that the photosphere emission is long-term stable and the broad Balmer lines are primarily collisonally excited. This scenario is consistent with the lack of variability, large Hα/Hβ ratios and little dust extinction, as well as the expected high gas density. Virial black hole mass estimates using broad Hα assuming photoionization are therefore highly questionable for LRDs.

@article{2025arXiv251116082B, author = {{Burke}, Colin J. and {Stone}, Zachary and {Shen}, Yue and {Jiang}, Yan-Fei}, title = {{Too Quiet for Comfort: Local Little Red Dots Lack Variability over Decades}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.16082}, pages = {arXiv:2511.16082}, archiveprefix = {arXiv}, eprint = {2511.16082}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251116082B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, local counterpart, spectroscopy, variability}, month_numeric = {11} }

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

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

The Astrophysical Journal, Nov 2025

Abs DOI ADS

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

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

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

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

arXiv e-prints, Nov 2025

Abs ADS arXiv

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

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

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

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

arXiv e-prints, Nov 2025

Abs ADS arXiv

The enigmatic Little Red Dots (LRDs) discovered by the James Webb Space Telescope (JWST) exhibit properties challenging their interpretation as common galaxies or Active Galactic Nuclei (AGN). Understanding their nature is key to placing them within our picture of early galaxy and massive black hole (MBH) evolution. To this aim, we build a realistic comparison between LRD observations with photometric properties of galaxies and AGN simulated by the L-GalaxiesBH model in a NIRCam mock sky. We model stellar continua and emission lines, the MBH emission from accretion disk, infrared radiation from dusty torus, and lines from narrow and broad line regions, accounting for dust attenuation and obscuration. Using realistic photometric cuts, we select a population of LRDs including both AGN and galaxies. The LRD fraction peaks at 40% (\sim10^-4\rm Mpc^-3) at z\sim4. Our LRDs are central galaxies spanning M_*=10^8-10^10.5\rm M_⊙. A population of galaxies with M_* 10^11.5\rm M_⊙, M_* > 10^9.5\rm M_⊙), and the interplay between AGN and galaxy emission drives the LRD selection. AGN dominate rest- frame UV-optical emission, while dust obscuration is secondary. LRDs host lighter MBHs (∼10^6.5\rm M_⊙) than non- LRDs (∼10^7.5\rm M_⊙), with fainter emission unable to balance their hosts Balmer breaks. We find no evidence for dominant heavy-seed origin of MBHs. LRD Galaxies (97% hosting MBHs) and LRD AGNs are disk-dominated, with LRD AGNs showing larger bulges formed mainly via disk instabilities.

@article{2025arXiv251110725H, author = {{Herrero-Carri{\'o}n}, Diego and {Spinoso}, Daniele and {Izquierdo-Villalba}, David and {Su}, Tong and {Bonoli}, Silvia and {Renard}, Pablo}, title = {{Back to basics: Little Red Dots as galaxies and dust-obscured AGNs in a synthetic NIRCam sky simulated with L-GalaxiesBH}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.10725}, pages = {arXiv:2511.10725}, archiveprefix = {arXiv}, eprint = {2511.10725}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251110725H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, early universe, photometry, simulation}, month_numeric = {11} }

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Supermassive Dark Stars and their remnants as a possible solution to three recent cosmic dawn puzzles

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

arXiv e-prints, Nov 2025

Abs ADS arXiv

The James Webb Space Telescope (JWST) begun to revolutionize our view of the Cosmos. The discovery of Blue Monsters (i.e. ultracompact yet very bright high-z galaxies) and the Little Red Dots (i.e. very compact dustless strong Balmer break cosmic dawn sources) pose significant challenges to pre-JWST era models of the assembly of first stars and galaxies. In addition, JWST data further strengthen the problem posed by the origin of the supermassive black holes that power the most distant quasars observed. Stars powered by Dark Matter annihilation (i.e. Dark Stars) can form out of primordial gas clouds during the cosmic dawn era and subsequently might grow via accretion and become supermassive. In this paper we argue that Supermassive Dark Stars (SMDSs) offer natural solutions to the three puzzles mentioned above. Moreover, we present the best evidence so far, for the existence of SMDSs: the identification of a He\raisebox -0.5ex\textasciitildeIIλ2511\raisebox-0.5ex~ Å absorption feature at S/N\sim4 in the spectrum of JADES-GS-z13-0.

@article{2025arXiv251108477I, author = {{Ilie}, Cosmin and {Paulin}, Jillian and {Petric}, Andreea and {Freese}, Katherine}, title = {{Supermassive Dark Stars and their remnants as a possible solution to three recent cosmic dawn puzzles}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = nov, eid = {arXiv:2511.08477}, pages = {arXiv:2511.08477}, archiveprefix = {arXiv}, eprint = {2511.08477}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251108477I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, spectroscopy, theory}, month_numeric = {11} }

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

Vasily Kokorev, John Chisholm, Rohan P. Naidu, and 18 more authors

arXiv e-prints, Nov 2025

Abs ADS arXiv

The detection of strong Balmer breaks and absorption features in Little Red Dots (LRDs) suggests they host AGN embedded within dense gas envelopes, potentially powered by super-Eddington accretion. We present GLIMPSE-17775, a luminous (L_\rm bol\sim10^45 erg s^-1) LRD at z=3.501 behind Abell S1063 (μ\sim2), observed with deep JWST/NIRCam and a \sim20 hr (80 hr de- lensed) NIRSpec/G395M spectrum. The data reveal 40+ emission and absorption features, including a rich forest of low-ionization FeII lines and numerous broad hydrogen recombination transitions. We use this depth to test the dense-gas interpretation through five independent diagnostics. Nearly all permitted lines show exponential wings with consistent FWHM, the signature of Thomson scattering requiring n_ersim10^8 cm^-3. Adopting this width yields M_\rm BH\sim10^6.7M_⊙, a factor of ten lower than Gaussian fits, and λ_\rm Edd\sim1.8. Additional diagnostics support the same picture: a pronounced Balmer break (f_ν,4050/f_ν,3670=2.0\pm0.1), enhanced HeI \lambda7065 and \lambda10830 with P-Cygni absorption, Bowen-fluorescent OI \lambda8446-\lambda11290 emission requiring Lyβ pumping, and 16 FeII lines matching fluorescence models. These features indicate a dense (n\sim10^8 cm^-3), partially ionized cocoon where scattering and fluorescence dominate line formation, providing strong evidence that at least some LRDs are powered by super-Eddington black-hole growth in the early Universe.

@article{2025arXiv251107515K, author = {{Kokorev}, Vasily and {Chisholm}, John and {Naidu}, Rohan P. and {Fujimoto}, Seiji and {Atek}, Hakim and {Brammer}, Gabriel and {Finkelstein}, Steven L. and {Akins}, Hollis B. and {Berg}, Danielle A. and {Furtak}, Lukas J. and {Fei}, Qinyue and {Hsiao}, Tiger Yu-Yang and {Matthee}, Jorryt and {Mu{\textasciitilde n}oz}, Julian B. and {Oesch}, Pascal A. and {Pan}, Richard and {Rinaldi}, Pierluigi and {Saldana-Lopez}, Alberto and {Schaerer}, Daniel and {Volonteri}, Marta and {Zitrin}, Adi}, title = {{The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.07515}, pages = {arXiv:2511.07515}, archiveprefix = {arXiv}, eprint = {2511.07515}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251107515K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, month_numeric = {11} }

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Balmer Absorption in Iron Low-ionization Broad Absorption Line Quasars

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

The Astrophysical Journal, Nov 2025

Abs DOI ADS

While C IV is the most common absorption line in broad absorption line quasar spectra, Balmer absorption lines (BALs) are among the rarest. We present analysis of Balmer absorption in a sample of 14 iron low-ionization BAL quasars (FeLoBALQs); eight are new identifications. We measured velocity offset, width, and apparent optical depth. The partial covering that is ubiquitous in BAL quasar spectra alters the measured Balmer optical depth ratios; accounting for this, we estimated the true H(n = 2) column density. We found the anticipated correlation between Eddington ratio and outflow speed, but it is weak in this sample because nearly all of the objects have the low outflow speeds characterizing loitering outflow FeLoBAL quasars, objects that are also found to have low accretion rates. Measurements of dN/dv, the differential column density with respect to the outflow speed, are anticorrelated with the luminosity and Eddington ratio: the strongest absorption is observed at the lowest speeds in the lowest-luminosity objects. The absorption line width is correlated with \ensuremathα_oi, the F_\ensuremathλ point-to-point slope between 5100 Å and 3 \ensuremathμm. This parameter is strongly correlated with the Eddington ratio among low-redshift quasars. BALs have been recently found in the spectra of little red dots (LRDs), a class of high-redshift objects discovered by JWST. We note suggestive similarities between LRDs and FeLoBAL quasars in the emission-line shape, the presence of steep reddening and a scattered blue continuum, the lack of hot dust emission, and X-ray weakness.

@article{2025ApJ...993..129L, author = {{Leighly}, Karen M. and {Gallagher}, Sarah C. and {Choi}, Hyunseop and {Terndrup}, Donald M. and {Voelker}, Julianna R. and {Richards}, Gordon T. and {Morabito}, Leah K.}, title = {{Balmer Absorption in Iron Low-ionization Broad Absorption Line Quasars}}, journal = {\apj}, keywords = {Broad-absorption line quasar, Quasars, 183, 1319}, year = {2025}, month = nov, volume = {993}, number = {1}, eid = {129}, pages = {129}, doi = {10.3847/1538-4357/ae04df}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...993..129L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, spectroscopy, x-ray}, month_numeric = {11} }

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The Balmer Break and Optical Continuum of Little Red Dots from Super-Eddington Accretion

Hanpu Liu, Yan-Fei Jiang, Eliot Quataert, and 2 more authors

The Astrophysical Journal, Nov 2025

Abs DOI ADS

The physical origin of little red dots (LRDs)—compact extragalactic sources with red rest-optical continua and broad Balmer lines—remains elusive. The redness of LRDs is likely intrinsic, suggesting optically thick gas emitting at a characteristic effective temperature of \ensuremath∼5000 K. Meanwhile, many LRD spectra exhibit a Balmer break, often attributed to absorption by a dense gas shell surrounding an active galactic nucleus. Using semianalytical atmosphere models and radiation transport calculations, we show that a super- Eddington accretion system can give rise to a Balmer break and a red optical color simultaneously, without invoking external gas absorption for the break or dust reddening. The break originates from a discontinuity in opacity across the Balmer limit, similar to that of early-type stars, but the lower photosphere density of super-Eddington systems, \ensuremathρ < 10^\ensuremath-9 g cm^\ensuremath-3, implies a significant opacity contrast even at a cool photosphere temperature of \ensuremath∼5000 K. Furthermore, while accretion in the form of a standard thin disk requires fine tuning to match the optical color of LRDs, an alternative scenario of a geometrically thick, roughly spherical accretion flow implies an effective temperature of 4000 K \ensuremath≲ T_eff \ensuremath≲ 6000 K that is very insensitive to the accretion rate (analogous to the Hayashi line in stellar models). The continuum spectra from the latter scenario align with the Balmer break and optical color of currently known LRDs. We discuss the predictions of our model and the prospects for more realistic spectra based on super- Eddington accretion simulations.

@article{2025ApJ...994..113L, author = {{Liu}, Hanpu and {Jiang}, Yan-Fei and {Quataert}, Eliot and {Greene}, Jenny E. and {Ma}, Yilun}, title = {{The Balmer Break and Optical Continuum of Little Red Dots from Super-Eddington Accretion}}, journal = {\apj}, keywords = {Active galactic nuclei, Radiative transfer, Accretion, 16, 1335, 14}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {113}, pages = {113}, doi = {10.3847/1538-4357/ae0c19}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994..113L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, sed, spectroscopy, theory}, month_numeric = {11} }

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

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

arXiv e-prints, Nov 2025

Abs ADS arXiv

We report the multiwavelength properties of eFEDS J084222.9+001000 (hereafter ID830), a quasar at z=3.4351, identified as the most X-ray luminous radio-loud quasar in the eROSITA Final Equatorial Depth Survey (eFEDS) field. ID830 shows a rest-frame 0.5-2 keV luminosity of \log (L_\mathrm0.5-2 keV/\mathrmerg~\mathrms^-1) = 46.20 \pm 0.12, with a steep X-ray photon index (Γ=2.43 \pm 0.21), and a significant radio counterpart detected with VLA/FIRST 1.4 GHz and VLASS 3 GHz bands. The rest-frame UV to optical spectra from SDSS and Subaru/MOIRCS J-band show a dust reddened quasar feature with A_\mathrmV = 0.39 \pm 0.08 mag and the expected bolometric AGN luminosity from the dust-extinction-corrected UV luminosity reaches L_\mathrmbol,3000= (7.62 \pm 0.31) \times 10^46 erg s^-1. We estimate the black hole mass of M_\mathrmBH = (4.40 \pm 0.72) \times 10^8 M_⊙ based on the MgIIλ2800 emission line width, and an Eddington ratio from the dust-extinction-corrected UV continuum luminosity reaches λ_\mathrmEdd,UV=1.44 \pm 0.24 and λ_\mathrmEdd,X = 12.8 \pm 3.9 from the X-ray luminosity, both indicating the super-Eddington accretion. ID830 shows a high ratio of UV-to-X-ray luminosities, α_\mathrmOX=-1.20 \pm 0.07 (or α_\mathrmOX=-1.42 \pm 0.07 after correcting for jet-linked X-ray excess), higher than quasars and little red dots in super-Eddington phase with similar UV luminosities, with α_\mathrmOX<-1.8. Such a high α_\mathrmOX suggests the coexistence of a prominent radio jet and X-ray corona, in this high Eddington accretion phase. We propose that ID830 may be in a transitional phase after an accretion burst, evolving from a super-Eddington to a sub-Eddington state, which could naturally describe the high α_\mathrmOX.

@article{2025arXiv251105029O, author = {{Obuchi}, Sakiko and {Ichikawa}, Kohei and {Yamada}, Satoshi and {Kawakatu}, Nozomu and {Liu}, Teng and {Matsumoto}, Naoki and {Merloni}, Andrea and {Takahashi}, Kosuke and {Zaw}, Ingyin and {Chen}, Xiaoyang and {Hada}, Kazuhiro and {Igo}, Zsofi and {Suh}, Hyewon and {Wolf}, Julien}, title = {{Discovery of an X-ray Luminous Radio-Loud Quasar at $z=3.4$: A Possible Transitional Super-Eddington Phase}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = nov, eid = {arXiv:2511.05029}, pages = {arXiv:2511.05029}, archiveprefix = {arXiv}, eprint = {2511.05029}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251105029O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, multi-wavelength, radio, sed, x-ray}, month_numeric = {11} }

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Little Red Dots are Nurseries of Massive Black Holes

Fabio Pacucci, Lars Hernquist, and Michiko Fujii

The Astrophysical Journal, Nov 2025

Abs DOI ADS

The James Webb Space Telescope has revealed a previously unknown population of compact, red galaxies at z \ensuremath∼ 5, known as “little red dots” (LRDs). With effective radii of \ensuremath∼100 pc and stellar masses of 10^9─10^11 M_\ensuremath⊙, a purely stellar interpretation implies extreme central densities, \ensuremathρ_\ensuremath⋆ \ensuremath∼ 10^4─10^5 M_\ensuremath⊙ pc^\ensuremath-3 and in some cases up to \ensuremath∼10^9 M_\ensuremath⊙ pc^\ensuremath-3, far exceeding those of globular clusters. At such densities, the dynamical friction time for 10 M_\ensuremath⊙ stars in the central 0.1 pc is <0.1 Myr, driving rapid mass segregation. We investigate the dynamical consequences of such an environment using (i) a Fokker─Planck analysis of long-term core evolution, (ii) an analytical model for the collisional growth of a very massive star (VMS), and (iii) direct N-body simulations. All approaches show that runaway collisions produce a VMS with mass 9 \texttimes 10^3 < M_VMS [M_\ensuremath⊙] < 5 \texttimes 10^4 within <1 Myr. Once the supply of massive stars is depleted, the VMS contracts on a \ensuremath∼8000 yr Kelvin─Helmholtz timescale and undergoes a general relativistic collapse, leaving a massive black hole of mass M_\ensuremath∙ \ensuremath∼ 10^4 M_\ensuremath⊙. We conclude that LRDs are natural nurseries for the formation of heavy black hole seeds via stellar-dynamical processes. This pathway produces seed number densities that far exceed those expected from direct collapse models and, owing to the dense residual stellar core, can sustain high rates of tidal disruption events.

@article{2025ApJ...994...40P, author = {{Pacucci}, Fabio and {Hernquist}, Lars and {Fujii}, Michiko}, title = {{Little Red Dots are Nurseries of Massive Black Holes}}, journal = {\apj}, keywords = {Early universe, Galaxies, Galaxy dynamics, Galaxy evolution, Intermediate-mass black holes, N-body simulations, 435, 573, 591, 594, 816, 1083}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {40}, pages = {40}, doi = {10.3847/1538-4357/ae1619}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994...40P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, month_numeric = {11} }

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Deciphering the Nature of Virgil: An Obscured Active Galactic Nucleus Lurking within an Apparently Normal Ly\ensuremathα Emitter during Cosmic Reionization

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

The Astrophysical Journal, Nov 2025

Abs DOI ADS

We present a comprehensive analysis of the MIRI Extremely Red Object Virgil, a Ly\ensuremathα emitter at z_spec = 6.6379 \ensuremath\pm 0.0035 with the photometric properties of a Little Red Dot. Leveraging new JWST/MIRI imaging from the MIDIS and PAHSPECS programs, we confirm Virgil’s extraordinary nature among galaxies in JADES/GOODS-South, exhibiting a strikingly red NIRCam-to-MIRI color (F444W─F1500W = 2.84 \ensuremath\pm 0.04 mag). Deep NIRSpec/PRISM spectroscopy from the OASIS program offers key insights into the host galaxy, revealing properties of an average star-forming galaxy during Cosmic Reionization, such as a subsolar metallicity, low-to-moderate dust content, and a relatively high ionization parameter and electron temperature. By estimating the star formation rate of Virgil from UV and H\ensuremathα, we find evidence that the galaxy is either entering or fading out of a bursty episode. Although line-ratio diagnostics employed at high z would classify Virgil as an active galactic nucleus (AGN), this classification becomes ambiguous once redshift evolution is considered. Nonetheless, Virgil occupies the same parameter space as recently confirmed AGNs at similar redshifts. The new deep MIRI data at 15 \ensuremathμm reinforce the AGN nature of Virgil, as inferred from multiple spectral energy distribution (SED) fitting codes. Virgil’s rising infrared SED and UV excess resemble those of Dust-Obscured Galaxies (DOGs) studied with Spitzer at Cosmic Noon, particularly blue-excess HotDOGs. Our results highlight the need for a multiwavelength approach incorporating MIRI to uncover such extreme sources at z \ensuremath≳ 6 and to shed light on the interplay between galaxy evolution and early black hole growth during Cosmic Reionization.

@article{2025ApJ...994...86R, author = {{Rinaldi}, Pierluigi and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Rieke}, George H. and {Lyu}, Jianwei and {D'Eugenio}, Francesco and {Wu}, Zihao and {Carniani}, Stefano and {Looser}, Tobias J. and {Shivaei}, Irene and {Boogaard}, Leindert A. and {Diaz-Santos}, Tanio and {Colina}, Luis and {{\"O}stlin}, G{\"o}ran and {Alberts}, Stacey and {{\'A}lvarez-M{\'a}rquez}, Javier and {Annuziatella}, Marianna and {Aravena}, Manuel and {Bhatawdekar}, Rachana and {Bunker}, Andrew J. and {Caputi}, Karina I. and {Charlot}, St{\'e}phane and {Crespo G{\'o}mez}, Alejandro and {Curti}, Mirko and {Eckart}, Andreas and {Gillman}, Steven and {Hainline}, Kevin and {Kumari}, Nimisha and {Hjorth}, Jens and {Iani}, Edoardo and {Inami}, Hanae and {Ji}, Zhiyuan and {Johnson}, Benjamin D. and {Jones}, Gareth C. and {Labiano}, {\'A}lvaro and {Maiolino}, Roberto and {Melinder}, Jens and {Moutard}, Thibaud and {Peissker}, Florian and {Rieke}, Marcia and {Robertson}, Brant and {Scholtz}, Jan and {Tacchella}, Sandro and {van der Werf}, Paul P. and {Walter}, Fabian and {Williams}, Christina C. and {Willott}, Chris and {Witstok}, Joris and {{\"U}bler}, Hannah and {Zhu}, Yongda}, title = {{Deciphering the Nature of Virgil: An Obscured Active Galactic Nucleus Lurking within an Apparently Normal Ly{\ensuremath{\alpha}} Emitter during Cosmic Reionization}}, journal = {\apj}, keywords = {Active galactic nuclei, High-redshift galaxies, Galaxy evolution, Near infrared astronomy, AGN host galaxies, Galaxy formation, Photoionization, Spectral energy distribution, Infrared astronomy, Galaxies, Infrared photometry, 16, 734, 594, 1093, 2017, 595, 2060, 2129, 786, 573, 792}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {86}, pages = {86}, doi = {10.3847/1538-4357/ae089c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994...86R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, sed, spectroscopy}, month_numeric = {11} }

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A little red dot at z = 7.3 within a large galaxy overdensity

Jan-Torge Schindler, Joseph F. Hennawi, Frederick B. Davies, and 11 more authors

Nature Astronomy, Nov 2025

Abs DOI ADS

The nature of ‘little red dots’ and their relation to other forms of accreting supermassive black holes remain an open question. Here we report the discovery of a little red dot at z = 7.3. It is attenuated by moderate amounts of dust, A_V = 2.79 mag, and has an intrinsic bolometric luminosity of 10^46.6 erg s^-1 and a supermassive black hole mass of 5 \texttimes 10^8 M_☉. Most notably, this object is embedded in an overdensity of eight nearby galaxies, allowing us to calculate a spectroscopic estimate of the clustering of galaxies around little red dots. We find a little red dot versus galaxy cross- correlation length of r_0 = 8 \ensuremath\pm 2 h^-1 cMpc, comparable to that of z \ensuremath≈ 6 ultraviolet-luminous quasars. The resulting estimate of their minimum dark matter halo mass log_10(M_halo ,min/M_☉ ) =12 .0_-1.0^+0.8 indicates that nearly all haloes above this mass must host actively accreting supermassive black holes at z \ensuremath≈ 7, in strong contrast with the far smaller duty cycle of luminous quasars (<1%). Our results, taken at face value, motivate a picture in which supermassive black holes in little red dot phases could serve as the obscured precursors of ultraviolet-luminous quasars, which provides a natural explanation for the short ultraviolet-luminous lifetimes inferred from both quasar clustering and quasar proximity zones.

@article{2025NatAs...9.1732S, author = {{Schindler}, Jan-Torge and {Hennawi}, Joseph F. and {Davies}, Frederick B. and {Bosman}, Sarah E. I. and {Endsley}, Ryan and {Wang}, Feige and {Yang}, Jinyi and {Barth}, Aaron J. and {Eilers}, Anna-Christina and {Fan}, Xiaohui and {Kakiichi}, Koki and {Maseda}, Michael and {Pizzati}, Elia and {Nanni}, Riccardo}, title = {{A little red dot at z = 7.3 within a large galaxy overdensity}}, journal = {Nature Astronomy}, year = {2025}, month = nov, volume = {9}, pages = {1732-1744}, doi = {10.1038/s41550-025-02660-1}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NatAs...9.1732S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, clustering, dust, early universe, spectroscopy}, month_numeric = {11} }

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A Deep Dive down the Broad-line Region: Permitted O I, Ca II, and Fe II Emission in an Active Galactic Nucleus Little Red Dot at z = 5.3

Roberta Tripodi, Maruša Bradač, Francesco D’Eugenio, and 27 more authors

The Astrophysical Journal Letters, Nov 2025

Abs DOI ADS

We present a spectroscopic analysis of a broad-line active galactic nucleus (AGN) selected as a little red dot (LRD) at z = 5.3 behind the Bullet cluster (Bz5.3) based on JWST/NIRCam and NIRSpec data. The detection of strong Fe II, O I, and Ca II triplet emission lines, along with the evidence of broad Balmer lines, provides strong evidence of a broad-line region (BLR) and an accreting supermassive black hole. Notably, we report the first detection of the \ensuremathλ1304 bump (i.e., a blend of O I \ensuremathλ1304 and Si II) at high redshift, a feature commonly seen in local AGNs but not yet reported in the early Universe. The O I \ensuremathλ1304/\ensuremathλ8446 photon ratio provides an independent measurement of dust attenuation in galaxies. In Bz5.3, this ratio is highly suppressed (0.1─0.3), implying significant internal dust extinction, with estimated dust attenuation A_V \ensuremath∼ 0.4─1.0. We identify Ly\ensuremathβ fluorescence as the dominant excitation mechanism of the low-ionization lines, with additional contributions from collisional excitation. High O I \ensuremathλ8446 equivalent width and weak O I \ensuremathλ7774 support this interpretation. The detection of iron emission, whether from broad permitted or narrow forbidden lines, supports the presence of a stratified BLR, as also recently proposed in local LRDs. Photoionization modeling of O I \ensuremathλ8446 and Ca II further suggests the coexistence of multiple gas phases with distinct densities and ionization states, highlighting the complexity of the BLR. Bz5.3 thus offers a rare window into early AGN activity and BLR physics at early times.

@article{2025ApJ...994L...6T, author = {{Tripodi}, Roberta and {Brada{\v{c}}}, Maru{\v{s}}a and {D'Eugenio}, Francesco and {Martis}, Nicholas and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Willott}, Chris and {Pentericci}, Laura and {Moreschini}, Bianca and {Markevitch}, Maxim and {Asada}, Yoshihisa and {Calabr{\'o}}, Antonello and {Desprez}, Guillaume and {Felicioni}, Giordano and {Gaspar}, Gaia and {Gonzalez}, Anthony H. and {Harshan}, Anishya and {Ji}, Xihan and {Jude{\v{z}}}, Jon and {Lemaux}, Brian C. and {Marconi}, Alessandro and {Markov}, Vladan and {Merida}, Rosa M. and {Napolitano}, Lorenzo and {Noirot}, Ga{\"e}l and {Parente}, Massimiliano and {Peter}, Annika H. G. and {Robbins}, Luke and {Robertson}, Andrew and {Sarrouh}, Ghassan T. E. and {Sawicki}, Marcin}, title = {{A Deep Dive down the Broad-line Region: Permitted O I, Ca II, and Fe II Emission in an Active Galactic Nucleus Little Red Dot at z = 5.3}}, journal = {\apjl}, keywords = {Astrophysical black holes, AGN host galaxies, Galaxy spectroscopy, 98, 2017, 2171}, year = {2025}, month = nov, volume = {994}, number = {1}, eid = {L6}, pages = {L6}, doi = {10.3847/2041-8213/ae13a9}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...994L...6T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, early universe, emission lines, jwst, spectroscopy}, month_numeric = {11} }

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Extreme properties of a compact and massive accreting black hole host in the first 500 Myr

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

Nature Communications, Nov 2025

Abs DOI ADS

Little red dots (LRDs) are a high redshift galaxy population. Despite their high number densities, their nature is still uncertain. Here we present CANUCS-LRD-z8.6, a spectroscopically confirmed little red dot at a spectroscopic redshift of z_spec = 8.6319, hosting an active galactic nucleus. Its spectrum exhibits broad H\ensuremathβ\ensuremathλ4863 Å emission, high-ionization lines (C iv, N iv]), high electron temperature, which are indicative of active galactic nucleus activity, and low metallicity (Z < 0.1\ensuremath-0.2Z_\ensuremath⊙). The inferred black hole mass, MBH=1.0\ensuremath-0.4+0.6\texttimes108M \ensuremath⊙, poses strong constraints on current black hole formation models and simulations. Additionally, its black hole is over-massive relative to its host, deviating from local M_BH \ensuremath- M_* relations, suggesting an early, rapid black hole growth preceding that of its galaxy. CANUCS-LRD-z8.6 may represent an evolutionary link between early massive black holes and the luminous quasars observed at z = 6.

@article{2025NatCo..16.9830T, author = {{Tripodi}, Roberta and {Martis}, Nicholas and {Markov}, Vladan and {Brada{\v{c}}}, Maru{\v{s}}a and {Di Mascia}, Fabio and {Cammelli}, Vieri and {D'Eugenio}, Francesco and {Willott}, Chris and {Curti}, Mirko and {Bhatt}, Maulik and {Gallerani}, Simona and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Singh}, Jasbir and {Gaspar}, Gaia and {Harshan}, Anishya and {Jude{\v{z}}}, Jon and {Merida}, Rosa M. and {Desprez}, Guillaume and {Sawicki}, Marcin and {Goovaerts}, Ilias and {Muzzin}, Adam and {Noirot}, Ga{\"e}l and {Sarrouh}, Ghassan T. E. and {Abraham}, Roberto and {Asada}, Yoshihisa and {Brammer}, Gabriel and {Estrada-Carpenter}, Vicente and {Felicioni}, Giordano and {Fujimoto}, Seiji and {Iyer}, Kartheik and {Mowla}, Lamiya and {Strait}, Victoria}, title = {{Extreme properties of a compact and massive accreting black hole host in the first 500 Myr}}, journal = {Nature Communications}, keywords = {Physical Sciences, Astronomical and Space Sciences}, year = {2025}, month = nov, volume = {16}, number = {1}, eid = {9830}, pages = {9830}, doi = {10.1038/s41467-025-65070-x}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NatCo..16.9830T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, host galaxy, spectroscopy}, month_numeric = {11} }

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Luminous mid-IR selected obscured quasars at cosmic noon in SDSS Stripe82 II: spectroscopic diversity and broad H \ensuremathα emissions

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

Monthly Notices of the Royal Astronomical Society, Nov 2025

Abs DOI ADS

We present a multiwavelength spectroscopic survey of 23 luminous mid- infrared-selected Type-2 quasars at the redshifts of ─3.49. The targets were selected in the SDSS Stripe 82 field based on their bright WISE 22 m detections and extremely faint or red optical counterparts. Near-infrared (Gemini/Gemini Near-InfraRed Spectrograph) and optical (Keck/Low Resolution Imaging Spectrometer and Keck Cosmic Web Imager Integral Field Spectrograph) spectroscopy confirm 23 out of 24 candidates as Type-2 quasars, including 12 objects at . The spectra exhibit strong rest-frame UV and optical emission lines (Ly , C IV, [O III], H ) with a wide range of line widths, indicating significant spectral diversity. Approximately one-third of the sample (8 of 23) shows broad H emission (full width at half- maximum, FWHM km s) despite their Type-2 classification, while the rest have only narrow lines (FWHM km s) characteristic of classical obscured quasars. Notably, these broad-line Type-2 quasars share similar spectral energy distributions with the James Webb Space Telescope (JWST)-discovered ’little red dot’, suggesting that our sample could be lower redshift analogues of the heavily obscured broad-line AGNs uncovered by JWST. We also find that the [O III] 5007 emission is relatively weak for their high-bolometric luminosities, deviating from trends seen in lower-z Type-2 quasi-stellar objects (QSOs). A new composite spectrum for Type-2 QSOs is built using our sample. Overall, our results demonstrate that mid-infrared selection efficiently uncovers diverse populations of obscured quasars and that spectroscopic follow-up is crucial for revealing their true nature. This study provides new insights into heavily obscured supermassive black hole growth at cosmic noon and bridges the gap to the obscured active galactic nuclei populations being revealed by JWST.

@article{2025MNRAS.544..687W, author = {{Wang}, Ben and {Ishikawa}, Yuzo and {Hennawi}, Joseph F. and {Cai}, Zheng and {Richards}, Gordon T. and {Zakamska}, Nadia L. and {Yang}, Daming and {Schindler}, Jan-Torge}, title = {{Luminous mid-IR selected obscured quasars at cosmic noon in SDSS Stripe82 II: spectroscopic diversity and broad H {\ensuremath{\alpha}} emissions}}, journal = {\mnras}, keywords = {galaxies: high-redshift, quasars: emission lines, quasars: general, quasars: supermassive black holes, infrared: galaxies}, year = {2025}, month = nov, volume = {544}, number = {1}, pages = {687-707}, doi = {10.1093/mnras/staf1730}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.544..687W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, multi-wavelength, non-jwst, spectroscopy}, month_numeric = {11} }

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Little red dots as embryos of active galactic nuclei

Jian-Min Wang, Yi-Lin Wang, Yong-Jie Chen, and 7 more authors

arXiv e-prints, Nov 2025

Abs ADS arXiv

As an unprecedented large population in the early universe, the JWST- discovered little red dots (LRDs) have garnered much attention for formation of massive black holes and galaxies, but their nature remains a mystery. The LRDs appearing as “Chimeras” like both active galactic nuclei (AGNs) and galaxies have stimulated renewed interest in the roadmap of central massive black hole (cMBH) formation in AGNs. In this paper, we suggest that the LRDs contain M_∙≲10^6 M_⊙ cMBHs as demonstrated by the Sołtan argument and there is a large population of stellar-mass black holes (sMBHs with total mass of \mathscrM_m_∙) embedded inside cMBH accretion disks (cMBH-disk) as motivated by anomalous reverberations of broad Hβ line in local AGNs. This embryo structure of LRDs (M_∙<\mathscrM_m_∙) is formed as a consequence of gravitational collapse of primordial clouds. In this Chimera, accretion onto sMBHs powers the rest- frame optical continuum of the LRDs but the UV continuum is jointly contributed by slim parts of the cMBH-disks and nuclear starbursts in the core of collapsing clouds governing the appearance of the observed V-shaped spectral energy distributions (SEDs). Outflowing clumped-envelopes are unavoidably formed by radiation pressure leading to absorption features of the Balmer lines. The present model works very well for LRDs’ SEDs and avoids the issues of overly massive cMBHs. Evolution of LRDs is briefly discussed including gravitational waves.

@article{2025arXiv251109278W, author = {{Wang}, Jian-Min and {Wang}, Yi-Lin and {Chen}, Yong-Jie and {Liu}, Jun-Rong and {Songsheng}, Yu-Yang and {Cheng}, Cheng and {Li}, Yan-Rong and {Du}, Pu and {Zhang}, Hao and {Zhao}, Yu}, title = {{Little red dots as embryos of active galactic nuclei}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.09278}, pages = {arXiv:2511.09278}, archiveprefix = {arXiv}, eprint = {2511.09278}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251109278W}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, sed, theory}, month_numeric = {11} }

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Little Red Dots host Black Hole Stars: A unified family of gas-reddened AGN revealed by JWST/NIRSpec spectroscopy

Anna de Graaff, Raphael E. Hviding, Rohan P. Naidu, and 34 more authors

arXiv e-prints, Nov 2025

Abs ADS arXiv

We use the DAWN JWST Archive to construct and characterise a sample of 116 little red dots (LRDs) across 2.3<z<9.3, selecting all sources with v-shaped UV-optical continua from NIRSpec/PRISM spectra and compact morphologies in NIRCam/F444W imaging. We show that LRD continuum spectra are ubiquitously well described by modified blackbodies across \raisebox-0.5ex\textasciitilde0.4-1.0μm, with typical T\raisebox-0.5ex\textasciitilde5000K or λ_peak\raisebox-0.5ex\textasciitilde0.65μm across 2 dex in luminosity, and a tail toward T\raisebox-0.5ex\textasciitilde2000K. LRDs therefore trace a locus in the Hertzsprung-Russell diagram that is directly analogous to stars on the Hayashi track, strongly supporting the picture that LRDs are AGN embedded in thermalised dense gas envelopes in approximate hydrostatic equilibrium. Hotter LRDs with λ_peak<0.65μm typically have strong Balmer breaks, redder UV slopes and high optical luminosities; other LRDs show weak or no Balmer breaks, and wide variety in β_UV and L_5100. Crucially, we demonstrate that the UV-optical continuum shapes and luminosities are strongly linked to the Hα, Hβ, [OIII] and OI line properties. There is a tight linear relation between the Hα and optical continuum luminosities, as well as Hα and OI_8446, indicating that Balmer, OI and optical emission must primarily be powered by the same source. The Balmer decrement increases strongly toward higher L_Hα, L_5100 and Balmer break strength, providing key evidence for luminosity-dependent effects of collisional (de-)excitation and resonant scattering in the gaseous envelopes. In contrast, we show that [OIII] emission likely originates from star-forming host galaxies, and that its strong correlation with Balmer break strength arises naturally from variation in the AGN-to-host ratio. Our work presents an empirical description of the nature and structure of LRDs, defining a new benchmark for ongoing LRD model developments.

@article{2025arXiv251121820D, author = {{de Graaff}, Anna and {Hviding}, Raphael E. and {Naidu}, Rohan P. and {Greene}, Jenny E. and {Miller}, Tim B. and {Leja}, Joel and {Matthee}, Jorryt and {Brammer}, Gabriel and {Katz}, Harley and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Bose}, Sownak and {Chisholm}, John and {Cleri}, Nikko J. and {Dayal}, Pratika and {Feldmann}, Robert and {Fudamoto}, Yoshinobu and {Fujimoto}, Seiji and {Furtak}, Lukas J. and {Glazebrook}, Karl and {Gottumukkala}, Rashmi and {Heintz}, Kasper E. and {Kokorev}, Vasily and {Labbe}, Ivo and {Maseda}, Michael V. and {McConachie}, Ian and {Nanayakkara}, Themiya and {Nelson}, Erica and {Nowaczyk}, Przemys{\l}aw and {Oesch}, Pascal A. and {Rix}, Hans-Walter and {Setton}, David J. and {Torralba}, Alberto and {Walter}, Fabian and {Wang}, Bingjie and {Weibel}, Andrea and {van der Wel}, Arjen}, title = {{Little Red Dots host Black Hole Stars: A unified family of gas-reddened AGN revealed by JWST/NIRSpec spectroscopy}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = nov, eid = {arXiv:2511.21820}, pages = {arXiv:2511.21820}, archiveprefix = {arXiv}, eprint = {2511.21820}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251121820D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, morphology, sed, spectroscopy}, month_numeric = {11} }

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Investigating Little Red Dots with UV Excess: Are They the High-redshift Siblings of Blue Hot Dust-obscured Galaxies?

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

The Astrophysical Journal, Oct 2025

Abs DOI ADS

Little red dots (LRDs), newly identified compact and dusty galaxies with an unexpectedly high number density observed by JWST, have an unusual “V-shaped” rest-frame UV to near-infrared spectral energy distribution (SED). A group of hyperluminous, obscured quasars with excess blue emission, called blue-excess hot dust- obscured galaxies (BHDs), also exhibit qualitatively similar SEDs to those of LRDs. They represent a rare population of galaxies hosting supermassive black holes (SMBHs) accreting near the Eddington limit at redshifts z \ensuremath∼ 1–4. In this study, we compare their multiwavelength SEDs to investigate whether LRDs, or a subset of them, could be high-redshift analogs of BHDs. Our analysis reveals that despite their similar “V-shape” SEDs, LRDs appear to be a different population than BHDs. The “V-shape” of BHDs appears at longer wavelengths compared to LRDs due to different selection strategies, suggesting LRDs have much less dust attenuation than typical BHDs. The bluer colors in the rest-frame infrared (continuum) emission of LRDs suggest the absence of hot dust heated by active galactic nuclei (AGN) accretion activities. We also argue that the blue excess in LRDs is unlikely from AGN scattered light. The compact morphologies and lower X-ray detection frequencies of LRDs suggest a distinct formation pathway from BHDs, which are thought to be powered by super- Eddington accretion onto central SMBHs following major galaxy mergers.

@article{2025ApJ...992..117B, author = {{Bao}, Lulu and {Tsai}, Chao-Wei and {Wu}, Jingwen and {Wang}, Tao and {Li}, Guodong and {Assef}, Roberto J. and {Diaz-Santos}, Tanio and {Eisenhardt}, Peter R. M. and {Stern}, Daniel and {Blain}, Andrew W.}, title = {{Investigating Little Red Dots with UV Excess: Are They the High-redshift Siblings of Blue Hot Dust-obscured Galaxies?}}, journal = {\apj}, keywords = {Infrared galaxies, Active galactic nuclei, High-redshift galaxies, Active galaxies, AGN host galaxies, 790, 16, 734, 17, 2017}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {117}, pages = {117}, doi = {10.3847/1538-4357/ae019e}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992..117B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, multi-wavelength, non-agn, sed}, month_numeric = {10} }

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A z\simeq0.4 Little Red Dot analog: An Extended Starburst with an Overmassive Black hole

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

arXiv e-prints, Oct 2025

Abs ADS arXiv

One of the most remarkable discoveries of JWST is a population of compact, red sources at z > 4, commonly referred to as Little Red Dots (LRDs). Spectroscopic identifications reported that most LRDs are active galactic nuclei (AGNs), which are preferentially found around z\raisebox-0.5ex\textasciitilde6 and could imply a key phase in the formation and growth of black holes (BHs) in the early universe. Photometric surveys at lower redshift have recently been carried out to trace their evolution across cosmic time, and a small number of LRDs have been spectroscopically identified at both Cosmic Noon and in the local universe. Here we report the discovery of one of the lowest-z analogs of LRDs, J204837.26-002437.2 (hereafter J2048) at z = 0.4332, using new Gemini-N/GMOS IFU observations combined with archival multi-band photometric SED data. The GMOS data reveal extended blue emission from starburst with a star formation rate of 400 Msun yr-1, together with an extended, highly fast ionized outflow. This is the first spectroscopic confirmation of extended host emission and outflow in an LRD- like galaxy, providing a unique laboratory for understanding the nature of their high-redshift counterparts. Moreover, J2048 would host an extremely overmassive BH with a BH-to-stellar mass ratio of 0.6, with the BH mass and host stellar mass estimated to be 10\^10.2 and 10\^10.4 Msun, respectively. We discuss the origin and evolutionary fate of J2048, and the implications that such low-z analogs have for interpreting the properties of high-z LRDs.

@article{2025arXiv251002801C, author = {{Chen}, Xiaoyang and {Ichikawa}, Kohei and {Akiyama}, Masayuki and {Inayoshi}, Kohei and {Inoue}, Akio K. and {Onoue}, Masafusa and {Toba}, Yoshiki and {Zavala}, Jorge A. and {Bakx}, Tom J. and {Kawaguchi}, Toshihiro and {Lee}, Kianhong and {Matsumoto}, Naoki and {Vijarnwannaluk}, Bovornpratch}, title = {{A $z\simeq0.4$ Little Red Dot analog: An Extended Starburst with an Overmassive Black hole}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.02801}, pages = {arXiv:2510.02801}, archiveprefix = {arXiv}, eprint = {2510.02801}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251002801C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, local counterpart, multi-wavelength, spectroscopy, starburst}, month_numeric = {10} }

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Seeding Cores: A Pathway for Nuclear Star Clusters from Bound Star Clusters in the First Billion Years

Fred Angelo Batan Garcia, Massimo Ricotti, and Kazuyuki Sugimura

The Open Journal of Astrophysics, Oct 2025

Abs DOI ADS

We model the formation of star clusters in a dwarf galaxy progenitor during the first 700 Myr of cosmic history using a cosmological radiation-hydrodynamic simulation with a sub-grid star formation efficiency (SFE) model calibrated from AU-scale radiation-MHD simulations of molecular clouds with varying mass, density, and metallicity. In comparison to a constant SFE model, our model yields more bursty star formation, a more abundant massive star cluster population, and overall a higher stellar mass. Clouds reach SFEs up to 80%, forming bound star clusters (densities , radii ) resembling those observed by the James Webb Space Telescope (JWST) in strongly lensed galaxies. Star clusters follow a flat power-law mass function with slope \ensuremathΓ\ensuremath∼\ensuremath-0.4. The most massive star clusters () grow through mergers and have metallicity spreads of 0.05\ensuremath-0.1 dex that roughly scale with mass. The second burst of star formation produce loosely bound star clusters with higher metallicities: at lower SFEs (2 - 20%). At z\ensuremath∼8.7, a nuclear star cluster (NSC) is seeded, growing 83% of its mass (, 20% of the galaxy’s stellar mass) through mergers with pre-existing clusters and the rest through in-situ star formation. The early formation of NSCs has interesting implications for seeding supermassive black holes and the population of little red dots recently discovered by JWST at z\ensuremath≳5.

@article{2025OJAp....8E.146G, author = {{Garcia}, Fred Angelo Batan and {Ricotti}, Massimo and {Sugimura}, Kazuyuki}, title = {{Seeding Cores: A Pathway for Nuclear Star Clusters from Bound Star Clusters in the First Billion Years}}, journal = {The Open Journal of Astrophysics}, year = {2025}, month = oct, volume = {8}, eid = {146}, pages = {146}, doi = {10.33232/001c.145064}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025OJAp....8E.146G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {175145281}, lrdkeys = {black hole mass, early universe, jwst, simulation, starburst}, month_numeric = {10} }

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

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

Astronomy & Astrophysics, Oct 2025

Abs DOI ADS

The physical nature of little red dots (LRDs), a population of compact red galaxies revealed by JWST, remains unclear. Photometric samples were constructed from varying selection criteria with limited spectroscopic follow-up available to test intrinsic spectral shapes and the prevalence of broad emission lines. We used the RUBIES survey, a large spectroscopic program with wide color-morphology coverage and homogeneous data quality, to systematically analyze the emission-line kinematics, spectral shapes, and morphologies of \ensuremath∼1500 galaxies at z > 3.1. We identified broad Balmer lines via a novel fitting approach that simultaneously models NIRSpec/PRISM and G395M spectra, yielding 80 broad-line sources with 28 (35%) at z > 6. A large subpopulation naturally emerged from the broad Balmer line sources, with 36 exhibiting v-shaped UV-to-optical continua and a dominant point source component in the rest-optical; we define these as spectroscopic LRDs, constituting the largest such sample to date. Strikingly, the spectroscopic LRD population is largely recovered when either a broad line or rest-optical point source is required in combination with a v-shaped continuum, suggesting an inherent link between these three defining characteristics. We compared the spectroscopic LRD sample to published photometric searches. Although these selections have high accuracy, 80%‑95% down to F444W < 26.5, only 50%‑80% of the RUBIES LRDs were photometrically identified, depending on the selection criteria used. The remainder were missed due to a mixture of faint rest-UV photometry, comparatively blue rest-optical colors, or highly uncertain photometric redshifts. Our findings highlight that well-selected spectroscopic campaigns are essential for robust LRD identification, while photometric criteria require refinement to capture the full population.

@article{2025A&A...702A..57H, author = {{Hviding}, Raphael E. and {de Graaff}, Anna and {Miller}, Tim B. and {Setton}, David J. and {Greene}, Jenny E. and {Labb{\'e}}, Ivo and {Brammer}, Gabriel and {Bezanson}, Rachel and {Boogaard}, Leindert A. and {Cleri}, Nikko J. and {Leja}, Joel and {Maseda}, Michael V. and {McConachie}, Ian and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Oesch}, Pascal A. and {Wang}, Bingjie and {Whitaker}, Katherine E. and {Williams}, Christina C.}, title = {{RUBIES: A spectroscopic census of little red dots: All point sources with v-shaped continua have broad lines}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift}, year = {2025}, month = oct, volume = {702}, eid = {A57}, pages = {A57}, doi = {10.1051/0004-6361/202555816}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...702A..57H}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {177925174}, lrdkeys = {emission lines, jwst, sample selection, sed, spectroscopy}, month_numeric = {10} }

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The M_\rm BH-M_* Relationship at 3<z<7: Big Black Holes in Little Red Dots

Brenda L. Jones, Dale D. Kocevski, Fabio Pacucci, and 25 more authors

arXiv e-prints, Oct 2025

Abs ADS arXiv

JWST has identified a large population of faint, broad-line active galactic nuclei (AGN) in the early universe that are powered by black holes (BHs) that often appear overmassive relative to their host galaxies. In this study, we examine the relationship between BH mass and galaxy stellar mass at 33σ above the relationship measured for local broad-line AGN. We derive an intrinsic scatter in this relationship of 0.9 dex, which does not vary over the redshift range of our sample. We also find that the M_\rm BH/M_⋆ ratio increases by 2.3 dex from z = 3.5 and z = 6.5 with a confidence level of > 3σ. We attribute this trend with the increasing fraction of LRDs in our sample at z>4 as their host masses are \sim1 dex lower than the non-LRD AGN in our sample. These results support a picture in which the BHs powering JWST’s broad-line AGN are genuinely overmassive and become increasingly so with redshift. We discuss the implications of our findings on early BH growth relative to that of their host galaxies and the constraints it places on BH seeding models.

@article{2025arXiv251007376J, author = {{Jones}, Brenda L. and {Kocevski}, Dale D. and {Pacucci}, Fabio and {Taylor}, Anthony J. and {Finkelstein}, Steven L. and {Buchner}, Johannes and {Trump}, Jonathan R. and {Somerville}, Rachel S. and {Hirschmann}, Michaela and {Yung}, L. Y. Aaron and {Barro}, Guillermo and {Bell}, Eric F. and {Bisigello}, Laura and {Calabro}, Antonello and {Cleri}, Nikko J. and {Dekel}, Avishai and {Dickinson}, Mark and {Gandolfi}, Giovanni and {Giavalisco}, Mauro and {Grogin}, Norman A. and {Inayoshi}, Kohei and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Napolitano}, Lorenzo and {Onoue}, Masafusa and {Ravindranath}, Swara and {Rodighiero}, Giulia and {Wilkins}, Stephen M.}, title = {{The $M\_{\rm BH}-M\_{*}$ Relationship at $3<z<7$: Big Black Holes in Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.07376}, pages = {arXiv:2510.07376}, archiveprefix = {arXiv}, eprint = {2510.07376}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251007376J}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, spectroscopy}, month_numeric = {10} }

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The BlueDOG at Cosmic Noon: A Possible Analog to Little Red Dots?

Seongjae Kim, Woong-Seob Jeong, Minjin Kim, and 3 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS

We discovered a hyperluminous dust-obscured galaxy with mysterious blue- excess emission (BlueDOG) in the rest-frame UV of its spectral energy distribution (SED) from a multiwavelength survey in the AKARI Deep Field - South (ADF-S). We present the results of SED analysis with multiwavelength photometric data and spectroscopic analysis, observed with Gemini-S/GMOS, FLAMINGOS-2, to explore the origin of blue-excess emission of a hyperluminous BlueDOG, ADFS-KMTDOG-102, at z = 2.6. The SED analysis shows that this BlueDOG is a highly massive system (log M_*/M_\ensuremath⊙ = 12.3) with substantial extinction. Additionally, the proportion of the old stellar population exceeds that of the young stellar population, which suggests stellar evolution cumulated from the early Universe. The mass of the supermassive black hole estimated using the extinction-corrected broad H\ensuremathα emission line yields log M_BH/M_\ensuremath⊙ = 10.2. We discuss the similarity between the BlueDOG and “Little Red Dots” (LRDs), recently discovered with the James Webb Space Telescope, showing SED shapes remarkably similar to those of LRDs. The UV emission line ratios indicate that the emission lines are primarily powered by the central active galactic nuclei (AGN). In contrast, the origin of the blue-excess UV continuum remains ambiguous, since both recent star formation and AGN-induced scattered light are viable explanations, based on the results from the SED fitting and scattered light modeling.

@article{2025ApJ...992...70K, author = {{Kim}, Seongjae and {Jeong}, Woong-Seob and {Kim}, Minjin and {Jun}, Hyunsung D. and {Yang}, Yujin and {Nakagawa}, Takao}, title = {{The BlueDOG at Cosmic Noon: A Possible Analog to Little Red Dots?}}, journal = {\apj}, keywords = {Active galaxies, High-redshift galaxies, Infrared galaxies, Supermassive black holes, 17, 734, 790, 1663}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {70}, pages = {70}, doi = {10.3847/1538-4357/adff59}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992...70K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, emission lines, sed, spectroscopy}, month_numeric = {10} }

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From nuclear star clusters to Little Red Dots: black hole growth, mergers, and tidal disruptions

Konstantinos Kritos and Joseph Silk

arXiv e-prints, Oct 2025

Abs ADS arXiv

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

@article{2025arXiv251021709K, author = {{Kritos}, Konstantinos and {Silk}, Joseph}, title = {{From nuclear star clusters to Little Red Dots: black hole growth, mergers, and tidal disruptions}}, journal = {arXiv e-prints}, keywords = {High Energy Astrophysical Phenomena, Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, General Relativity and Quantum Cosmology}, year = {2025}, month = oct, eid = {arXiv:2510.21709}, pages = {arXiv:2510.21709}, archiveprefix = {arXiv}, eprint = {2510.21709}, primaryclass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251021709K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, theory}, month_numeric = {10} }

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

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

The Astrophysical Journal, Oct 2025

Abs DOI ADS

JWST has revealed a large population of compact, red objects at z > 4 known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 88 LRDs from the JWST PRIMER survey with complete photometric coverage from 1 to 18 \ensuremathμm using NIRCam and MIRI imaging, representing the most extensive SED analysis on a large LRD sample with long-wavelength MIRI data. We examine SED models in which either galaxy or active galactic nucleus (AGN) emission dominates the rest-frame UV or optical continuum, extracting physical properties to explore each scenario’s implications. In the galaxy-only model, we find massive, dusty stellar populations alongside unobscured, low- mass components, hinting at inhomogeneous obscuration. The AGN- only model indicates dusty, luminous AGNs with low hot dust fractions compared to typical quasars. A hybrid AGN and galaxy model suggests low-mass, unobscured galaxies in the UV, with stellar mass estimates spanning \ensuremath∼2 dex across the different models, underscoring the need for caution in interpreting LRD stellar masses. With MIRI photometry, the galaxy-only model produces stellar masses within cosmological limits, but extremely high stellar mass densities are inferred. The hybrid model infers highly overmassive black holes exceeding those in recently reported high-redshift AGNs, hinting at a partial AGN contribution to the rest-optical continuum or widespread super-Eddington accretion. Our findings highlight the extreme conditions required for both AGN- and galaxy-dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.

@article{2025ApJ...992...26L, author = {{Leung}, Gene C. K. and {Finkelstein}, Steven L. and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Morales}, Alexa M. and {Taylor}, Anthony J. and {Barro}, Guillermo and {Kocevski}, Dale D. and {Akins}, Hollis B. and {Carnall}, Adam C. and {Ch{\'a}vez Ortiz}, {\'O}scar A. and {Cleri}, Nikko J. and {Cullen}, Fergus and {Donnan}, Callum T. and {Dunlop}, James S. and {Ellis}, Richard S. and {Grogin}, Norman A. and {Hirschmann}, Michaela and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Lucas}, Ray A. and {McLeod}, Derek J. and {Papovich}, Casey and {Yung}, L. Y. Aaron}, title = {{Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging}}, journal = {\apj}, keywords = {Active galactic nuclei, Galaxy formation, High-redshift galaxies, Supermassive black holes, 16, 595, 734, 1663}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {26}, pages = {26}, doi = {10.3847/1538-4357/adfcce}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992...26L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, non-agn, photometry, sed}, month_numeric = {10} }

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A big red dot at cosmic noon

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

Astronomy & Astrophysics, Oct 2025

Abs DOI ADS

We report the discovery of a little red dot (LRD), dubbed BiRD (’big red dot’), at z \ensuremath∼ 2.33 in the field around the z \ensuremath∼ 6.3 quasar SDSS J1030+0524. Using JWST/NIRCam images, we identified it as a bright outlier in the F200W \ensuremath- F356W color versus F356W magnitude diagram of point sources in the field. The NIRCam/WFSS spectrum reveals the emission from He I\ensuremathλ 10830 and Pa\ensuremathγ line, both displaying a narrow and a broad (FWHM \ensuremath≳ 2000 km s^\ensuremath-1) component. The He I line is affected by an absorption feature, tracing dense gas with He I column density in the 2^3S level N(He I) \ensuremath∼ 0.5 \ensuremath- 1.2 \texttimes 10^14 cm^\ensuremath-2, depending on the location of the absorber, which is outflowing at a speed of \ensuremath∆ v = \ensuremath- 830 \ensuremath- 148 + 131 km s^\ensuremath-1. As observed in the majority of LRDs, BiRD does not exhibit any X-ray or radio emission down to 3.7 \texttimes 10^42 erg s^\ensuremath-1 and 3 \texttimes 10^39 erg s^\ensuremath-1, respectively. The black hole mass and the bolometric luminosity, both inferred from the Pa\ensuremathγ broad component, amount to M_BH \ensuremath∼ 10^8 M_\ensuremath⊙ and L_bol \ensuremath∼ 3 \texttimes 10^45 erg s^\ensuremath-1, respectively. Intriguingly, BiRD presents strict analogies with other two LRDs spectroscopically confirmed at cosmic noon, namely, GN-28074 (nicknamed Rosetta Stone) at z \ensuremath∼ 2.26 and RUBIES-BLAGN-1 at z \ensuremath∼ 3.1. The blueshifted He I absorption detected for all three sources suggests that gas outflows could be common in LRDs. We derived a first estimate of the space density of LRDs at z \ensuremath∼ 2 \ensuremath- 3 based on JWST data, as a function of the bolometric luminosity and black hole mass. The space density \ensuremathΦ ( L ) = 4 . 0 \ensuremath- 2.4 + 4.0 \texttimes 10 \ensuremath- 6 Mpc^\ensuremath-3 dex^\ensuremath-1 is only a factor of \ensuremath∼2 \ensuremath- 3 lower than that of UV- selected quasars with comparable bolometric luminosity and redshift, meaning that the contribution of LRDs to the broader AGN population is also relevant at cosmic noon. A similar trend has also been observed with respect to black hole masses. As suggested by recent theories, if LRDs can indeed serves as probes of the very first and rapid growth of black hole seeds, our finding suggests that the formation of black hole seeds continues to be efficient at least up to cosmic noon.

@article{2025A&A...703A..36L, author = {{Loiacono}, Federica and {Gilli}, Roberto and {Mignoli}, Marco and {Mazzolari}, Giovanni and {Decarli}, Roberto and {Brusa}, Marcella and {Calura}, Francesco and {Chiaberge}, Marco and {Comastri}, Andrea and {D'Amato}, Quirino and {Iwasawa}, Kazushi and {Juod{\v{z}}balis}, Ignas and {Lanzuisi}, Giorgio and {Maiolino}, Roberto and {Marchesi}, Stefano and {Norman}, Colin and {Peca}, Alessandro and {Prandoni}, Isabella and {Sapori}, Matteo and {Signorini}, Matilde and {Tozzi}, Paolo and {Vanzella}, Eros and {Vignali}, Cristian and {Vito}, Fabio and {Zamorani}, Gianni}, title = {{A big red dot at cosmic noon}}, journal = {\aap}, keywords = {galaxies: active, galaxies: high-redshift, quasars: absorption lines, quasars: supermassive black holes}, year = {2025}, month = oct, volume = {703}, eid = {A36}, pages = {A36}, doi = {10.1051/0004-6361/202555946}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...703A..36L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {178133386}, lrdkeys = {black hole mass, emission lines, jwst, multi-wavelength, spectroscopy}, month_numeric = {10} }

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Modeling the “Dark-matter Dominated” Dwarf Galaxy Segue 1 with a Supermassive Black Hole

Nathaniel Lujan, Karl Gebhardt, Richard Anantua, and 11 more authors

The Astrophysical Journal Letters, Oct 2025

Abs DOI ADS

The dwarf spheroidal galaxy, Segue 1, is thought to have one of the largest ratios of dark matter to stellar mass. Using orbit-based dynamical models, we model Segue 1, including a dark halo and a central black hole. The best-fit model requires a black hole mass of 4.5 \ensuremath\pm 1.5 \texttimes 10^5 M_\ensuremath⊙. The value of the black hole mass is similar either with or without a dark halo. The mass-to-light ratio of the stars is poorly constrained by the dynamical modeling, reflecting that Segue 1 is dominated by mass other than stars. Dynamical models that exclude a black hole provide a worse fit and require a dark halo with very-small-scale radii of below 100 pc. Additionally, the zero black hole models require a stellar orbital distribution that is highly radially biased. The model with a black hole provides an orbital structure that is close to isotropic, more similar to other well-studied systems. We argue that the two-parameter models of stars and black hole provide a better description of Segue 1 than the three-parameter models of stars and two dark halo components. Additional support for a central black hole comes from a significant increase in the central rotation. Using individual velocities, we measure a rotation amplitude of 9.0 \ensuremath\pm 2.4 km s^‑1. Segue 1 is likely being tidally stripped at large radii, and we might be witnessing the remnant nucleus of a more massive system. Alternatively, given the high black hole mass relative to the stellar mass, Segue 1 is analogous to the Little Red Dots seen in the early Universe.

@article{2025ApJ...992L..25L, author = {{Lujan}, Nathaniel and {Gebhardt}, Karl and {Anantua}, Richard and {Chase}, Owen and {Debski}, Maya H. and {Finley}, Claire and {Gomez}, Loraine V. and {Gupta}, Om and {Lawson}, Alex J. and {Marron}, Izabella and {Martinez}, Zorayda and {Painter}, Connor A. and {Sklansky}, Yonatan and {West}, Hayley}, title = {{Modeling the ``Dark-matter Dominated'' Dwarf Galaxy Segue 1 with a Supermassive Black Hole}}, journal = {\apjl}, keywords = {Black holes, 162}, year = {2025}, month = oct, volume = {992}, number = {2}, eid = {L25}, pages = {L25}, doi = {10.3847/2041-8213/ae0b4f}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992L..25L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, kinematics, local counterpart, non-agn, non-jwst}, altmetric = {182950411}, month_numeric = {10} }

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The rise and fall of Little Red Dots could be driven by the environment

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

arXiv e-prints, Oct 2025

Abs ADS arXiv

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

@article{2025arXiv251006408M, author = {{M{\'e}rida}, Rosa M. and {Gaspar}, Gaia and {Asada}, Yoshihisa and {Sawicki}, Marcin and {Omori}, Kiyoaki Christopher and {Willott}, Chris J. and {Martis}, Nicholas S. and {Muzzin}, Adam and {Noirot}, Ga{\"e}l and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Sarrouh}, Ghassan T. E. and {Tripodi}, Roberta}, title = {{The rise and fall of Little Red Dots could be driven by the environment}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.06408}, pages = {arXiv:2510.06408}, archiveprefix = {arXiv}, eprint = {2510.06408}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251006408M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, morphology, sed, spectroscopy}, month_numeric = {10} }

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Evidence of violation of Case B recombination in Little Red Dots

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

arXiv e-prints, Oct 2025

Abs ADS arXiv

Little Red Dots (LRDs) are a new class of compact extragalactic objects, with a v-shaped optical spectral energy distribution breaking close to the Balmer break wavelength, and broad, typically exponentially-shaped lines. They are believed to be supermassive black holes surrounded by very dense, ionized gas, leading us to explore for any departures from Case B recombination by examining the ratios of multiple hydrogen Balmer lines: Hα, Hβ, Hγ, and Hδ. We analyze a dozen high-S/N LRDs with JWST/NIRSpec, measuring Balmer ratios in the seven objects with coverage of at least three lines. We decompose the line ratios into their respective broad and narrow components. Broad line ratios are consistent with Case B plus dust extinction in all objects but one, RUBIES EGS-49140, which departs from Case B expectations by more than 5σ. The narrow components are consistent with minimal dust attenuation, while two objects exhibit narrow Hα/Hβ≈1.8. Such low decrements are observed in highly ionized density bounded nebulae, associated with starburst environments. Nevertheless, both flat decrement cases can be reconciled assuming an unresolved absorption feature. RUBIES EGS-49140, shows a high broad Hα/Hβ, but Hγ/Hα and Hδ/Hα ratios are lower than expected for extinction-modified Case B, hinting at an unphysically steep dust law. These line ratios may be due to increased optical depth in the Balmer lines, as a direct effect of high density (logn_e > 9) gas surrounding the black hole. If Case B recombination does hold in most LRDs, they must be moderate-to- heavily dust obscured (A_V\simeq1-8) while the host-galaxy should be dust-free, suggesting that the extinction in the broad lines is local to the LRD and not due to the general ISM of the host galaxy.

@article{2025arXiv251006362N, author = {{Nikopoulos}, G. P. and {Watson}, D. and {Sneppen}, A. and {Rusakov}, V. and {Heintz}, K. E. and {Witstok}, J. and {Brammer}, G.}, title = {{Evidence of violation of Case B recombination in Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.06362}, pages = {arXiv:2510.06362}, archiveprefix = {arXiv}, eprint = {2510.06362}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251006362N}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, emission lines, jwst, sed, spectroscopy}, month_numeric = {10} }

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Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

P. Rinaldi, N. Bonaventura, G. H. Rieke, and 31 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS

We analyze 99 photometrically selected Little Red Dots (LRDs) at z \ensuremath≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes \ensuremath≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest- frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M\ens uremath⋆/M\ensuremath⊙)=9.07‑0.08+0.11 for pure stellar models with AV\ensuremath≈1.16‑0.21+0.11 mag, and log10(M\ensuremath⋆/M\ensuremath⊙)=9.67‑0.27 +0.17 for models including active galactic nuclei (AGNs) with AV\ensuremath≈2.74‑0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad H\ensuremathα is detected in 40% (FWHM = 1200–2900 km s^‑1), and one source shows broad H\ensuremathβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

@article{2025ApJ...992...71R, author = {{Rinaldi}, P. and {Bonaventura}, N. and {Rieke}, G. H. and {Alberts}, S. and {Caputi}, K. I. and {Baker}, W. M. and {Baum}, S. and {Bhatawdekar}, R. and {Bunker}, A. J. and {Carniani}, S. and {Curtis-Lake}, E. and {D'Eugenio}, F. and {Egami}, E. and {Ji}, Z. and {Johnson}, B. D. and {Hainline}, K. and {Helton}, J. M. and {Lin}, X. and {Lyu}, J. and {Ma}, Z. and {Maiolino}, R. and {P{\'e}rez-Gonz{\'a}lez}, P. G. and {Rieke}, M. and {Robertson}, B. E. and {Shivaei}, I. and {Stone}, M. and {Sun}, Y. and {Tacchella}, S. and {{\"U}bler}, H. and {Williams}, C. C. and {Willmer}, C. N. A. and {Willott}, C. and {Zhang}, J. and {Zhu}, Y.}, title = {{Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots}}, journal = {\apj}, keywords = {James Webb Space Telescope, Active galactic nuclei, Near infrared astronomy, Galaxy evolution, Galaxy formation, 2291, 16, 1093, 594, 595}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {71}, pages = {71}, doi = {10.3847/1538-4357/adfa10}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992...71R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, jwst, morphology, photometry, sed}, month_numeric = {10} }

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Ultra-Strongly Self-Interacting Dark Matter: From Phenomenology to Astrophysical Observables

M. Grant Roberts, Wolfgang Altmannshofer, Pierce Giffin, and 1 more author

arXiv e-prints, Oct 2025

Abs ADS arXiv

We develop a minimal, testable framework for two-component self- interacting dark matter (SIDM) in which a dominant, moderately self-interacting species coexists with an ultra-strongly self- interacting subcomponent (uSIDM). A light vector mediator induces velocity-dependent self-scattering, while early-universe dynamics - standard 2 \to 2 annihilation supplemented by interconversion χ_1χ_1 \to χ_2χ_2 - determine the relic abundance analytically. From observations of dwarf and low surface brightness galaxy rotation curves, as well as strong cluster lensing, we place constraints on the microphysics parameters. From these constrained regions, we map the microphysics to effective \textbackslashtexttt{ETHOS} parameters and evolve the linear power spectrum in \textbackslashtexttt{CLASS}. We then confront the model with direct-detection constraints and place an upper bound on our parameter space. We identify a region where: (1) the SIDM dominant component attains σ_\rmeff/m = 20 - 40~\textcm^2\textg^-1 at dwarf velocities while satisfying cluster upper bounds σ_\rmeff/m < 0.13~\rmcm^2\rmg^-1; (2) a subpercent uSIDM fraction drives accelerated gravothermal collapse in early halos, providing seeds relevant to high-redshift quasar formation and “little red dots”; and (3) the small-scale cutoff in the matter power spectrum remains consistent with Lyman-α and satellite counts, but exhibits non-standard features, potentially discernible with future observations. The allowed space can be organized by the mediator-to-DM mass ratio and the late-time uSIDM fraction, with a narrow window singled out by the combined cosmological and astrophysical requirements.

@article{2025arXiv251018142R, author = {{Roberts}, M. Grant and {Altmannshofer}, Wolfgang and {Giffin}, Pierce and {Profumo}, Stefano}, title = {{Ultra-Strongly Self-Interacting Dark Matter: From Phenomenology to Astrophysical Observables}}, journal = {arXiv e-prints}, keywords = {High Energy Physics - Phenomenology, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = oct, eid = {arXiv:2510.18142}, pages = {arXiv:2510.18142}, archiveprefix = {arXiv}, eprint = {2510.18142}, primaryclass = {hep-ph}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251018142R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, multi-wavelength, simulation, theory, x-ray}, month_numeric = {10} }

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

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

arXiv e-prints, Oct 2025

Abs ADS arXiv

JWST has revealed a population of red, compact, high-redshift (z\sim3-10) objects referred to as “Little Red Dots“ (LRDs). These objects exhibit unusual spectral features reminiscent of stellar spectra with blackbody-like SEDs, large hydrogen Balmer breaks, Balmer line absorption, and classical stellar absorption features such as calcium H&K and the calcium triplet. Following the recent suggestion that these may be actively accreting direct-collapse black holes in the process of assembly, i.e. quasi-stars, we present evolutionary models of quasi-stars using our recently released, publicly available MESA-QUEST modeling framework. We compute a grid of models spanning a range of black hole masses and predict the luminosities, temperatures, surface gravities, and lifetimes of these objects. We find that these models lie along a Hayashi track once they hit their “late-stage” which constitutes the majority of their lives (∼20\raisebox-0.5ex\textasciitildeMyr). We present scaling relations for estimating the mass of a quasi-star as a function of the bolometric luminosity, as well as the bolometric luminosity as a function of the effective temperature for the Hayashi track. The short lifetimes in tandem with the observed number density of LRDs imply the possibility that every supermassive black hole was once a quasi-star. We compare synthetic spectra of our quasi-star models to observations of LRDs, and show that these models are broadly capable of reproducing the continuum spectra of observed LRDs. These results indicate that quasi-stars are promising candidates for the origin of supermassive black holes via direct collapse in the early universe.

@article{2025arXiv251017952S, author = {{Santarelli}, Andrew D. and {Farag}, Ebraheem and {Bellinger}, Earl P. and {Natarajan}, Priyamvada and {Naidu}, Rohan P. and {Campbell}, Claire B. and {Caplan}, Matthew E.}, title = {{Evolutionary Tracks and Spectral Properties of Quasi-stars and Their Correlation with Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, High Energy Astrophysical Phenomena}, year = {2025}, month = oct, eid = {arXiv:2510.17952}, pages = {arXiv:2510.17952}, archiveprefix = {arXiv}, eprint = {2510.17952}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251017952S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, sed, spectroscopy, theory}, month_numeric = {10} }

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Faint active galactic nuclei supplied 31-75% of hydrogen-ionizing photons at z>5

Mainak Singha, Sangeeta Malhotra, and James Ely Rhoads

arXiv e-prints, Oct 2025

Abs ADS arXiv

The origin of the ionizing photons that completed hydrogen reionization remains debated. Using recent JWST and ground-based surveys at 4.5 <= z <= 6.5, we construct a unified rest-UV AGN luminosity function that separates unobscured Type I and obscured Type II populations, and show that “little red dots” and X-ray selected sources are magnitude-filtered subsets of Type I with a mixture fraction eta = 0.10 +/- 0.02. We anchor the Lyman- continuum (LyC) escape fraction to outflow incidence and geometric clearing rather than assuming quasar-like values for all classes, and propagate uncertainties through a joint fit. Integrating over -27 < M_UV < -17, AGN inject Ndot_ion,AGN = (3.77 +1.08/-0.95) x 10\^51 s\^-1 Mpc\^-3, nearly twice earlier estimates and comparable to the Ly-alpha inferred requirement at z \raisebox-0.5ex~6. When combined with the JWST galaxy UV luminosity function and a harder stellar ionizing efficiency of log10(xi_ion) = 25.7, AGN contribute 31-75% of the total ionizing photons for representative galaxy escape fractions f_esc,gal = 0.03-0.20. The resulting hydrogen photoionization rate, Gamma_HI \raisebox-0.5ex~(0.5-2) x 10\^-12 s\^-1 at z \raisebox-0.5ex~5-6, lies squarely within the Ly-alpha forest constraints once mean free paths and IGM clumpiness are accounted for, remaining consistent for combined AGN-galaxy models up to f_esc,gal <= 5%. These results suggest that AGN and galaxies jointly sustained the ionizing background during the final stages of reionization, with AGN remaining a major but not exclusive contributor.

@article{2025arXiv251026990S, author = {{Singha}, Mainak and {Malhotra}, Sangeeta and {Ely Rhoads}, James}, title = {{Faint active galactic nuclei supplied 31-75\% of hydrogen-ionizing photons at z>5}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.26990}, pages = {arXiv:2510.26990}, archiveprefix = {arXiv}, eprint = {2510.26990}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251026990S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, multi-wavelength, photometry}, month_numeric = {10} }

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Mephisto: Self-Improving Large Language Model-Based Agents for Automated Interpretation of Multi-band Galaxy Observations

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

arXiv e-prints, Oct 2025

Abs ADS arXiv

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

@article{2025arXiv251008354S, author = {{Sun}, Zechang and {Ting}, Yuan-Sen and {Liang}, Yaobo and {Duan}, Nan and {Huang}, Song and {Cai}, Zheng}, title = {{Mephisto: Self-Improving Large Language Model-Based Agents for Automated Interpretation of Multi-band Galaxy Observations}}, journal = {arXiv e-prints}, keywords = {Instrumentation and Methods for Astrophysics, Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.08354}, pages = {arXiv:2510.08354}, archiveprefix = {arXiv}, eprint = {2510.08354}, primaryclass = {astro-ph.IM}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251008354S}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, multi-wavelength, photometry, sed, starburst}, month_numeric = {10} }

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JWST/NIRSpec Observations of High-ionization Emission Lines in Galaxies at High Redshift

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

The Astrophysical Journal, Oct 2025

Abs DOI ADS

JWST spectroscopy has built large emission line samples at z \ensuremath≳ 4, but it has yet to confidently reveal many galaxies with the hard radiation fields commonly associated with active galactic nucleus photoionization. While this may indicate a weaker UV ionizing spectrum in many z > 4 active galactic nuclei or obscuration from dense neutral gas and dust, the complete picture remains unclear owing to the small number of deep rest-UV spectra. Here, we characterize the strength of high-ionization lines in 53 new galaxies observed with NIRSpec R = 2700 grating spectroscopy. We present new detections of narrow N V \ensuremathλ1240 in two galaxies. One is a previously confirmed z = 6.98 little red dot (LRD) with broad H\ensuremathβ, and the other is a z = 8.72 galaxy with a narrow-line spectrum. Neither source exhibits C IV or He II emission, indicating large N V/C IV and N V/He II ratios that may reflect a combination of nitrogen-enhancement and resonant scattering effects. We investigate the incidence of narrow high- ionization lines in a large database of 851 NIRSpec grating spectra, and we separately quantify the fraction of LRDs with narrow high-ionization UV emission lines. Our results likely suggest that hard radiation fields are indeed present in a small subset of LRDs (12.5‑10.4+23.7%) and UV-selected galaxies (2.2‑1.0+1.7%) at z > 4. The identification of narrow high- ionization lines in the population of LRDs with strong Balmer absorption suggests that the dense neutral hydrogen gas may not uniformly cover the nucleus. The strong N V (coupled with weak C IV and He II) suggests that efforts to identify high-ionization lines should extend down in wavelength to the N V doublet.

@article{2025ApJ...991..217T, author = {{Tang}, Mengtao and {Stark}, Daniel P. and {Plat}, Ad{\`e}le and {Feltre}, Anna and {Katz}, Harley and {Senchyna}, Peter and {Mason}, Charlotte A. and {Whitler}, Lily and {Chen}, Zuyi and {Topping}, Michael W.}, title = {{JWST/NIRSpec Observations of High-ionization Emission Lines in Galaxies at High Redshift}}, journal = {\apj}, keywords = {High-redshift galaxies, Active galactic nuclei, 734, 16}, year = {2025}, month = oct, volume = {991}, number = {2}, eid = {217}, pages = {217}, doi = {10.3847/1538-4357/adfd57}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...991..217T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, emission lines, jwst, non-agn, spectroscopy}, month_numeric = {10} }

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A Novel Formation Channel for Supermassive Black Hole Binaries in the Early Universe via Primordial Black Holes

Saiyang Zhang, Boyuan Liu, and Volker Bromm

The Astrophysical Journal, Oct 2025

Abs DOI ADS

We present a novel formation channel for supermassive black hole (SMBH) binaries in the early Universe, driven by primordial black holes (PBHs). Using high-resolution hydrodynamical simulations, we explore the role of massive PBHs (m_BH \ensuremath∼ 10^6 M_\ensuremath⊙) in catalyzing the formation of direct-collapse black holes (DCBHs), providing a natural in situ pathway for binary SMBH formation. PBHs enhance local overdensities, accelerate structure formation, and exert thermal feedback on the surrounding medium via accretion. Lyman–Werner radiation from accreting PBHs suppresses H_2 cooling, shifting the dominant gas coolant to atomic hydrogen. When combined with significant baryon–dark matter streaming velocities (v_b\ensuremathχ \ensuremath≳ 0.8\ensuremathσ_b\ensuremathχ, where \ensuremathσ_b\ensuremathχ is the rms streaming velocity), these effects facilitate the formation of dense, gravitationally unstable atomically cooling gas clouds in the PBH’s wake. These clouds exhibit sustained high inflow rates (Ṁinfall\ensuremath≳0.1‑0.01M\ensuremath⊙ yr^‑1), providing ideal conditions for DCBH formation from rapidly growing supermassive stars of \ensuremath∼10^5 M_\ensuremath⊙ at redshift z \ensuremath∼ 20–10. The resulting systems form SMBH binaries with initial mass ratios q\ensuremath∼O(0.1) and separations of \ensuremath∼10 pc. Such PBH-DCBH binaries provide testable predictions for JWST and Atacama Large Millimeter/submillimeter Array, potentially explaining select high-z sources like little red dots, and represent gravitational-wave sources for future missions like LISA and TianQin—bridging early-Universe black hole physics, multimessenger astronomy, and dark matter theory.

@article{2025ApJ...992..136Z, author = {{Zhang}, Saiyang and {Liu}, Boyuan and {Bromm}, Volker}, title = {{A Novel Formation Channel for Supermassive Black Hole Binaries in the Early Universe via Primordial Black Holes}}, journal = {\apj}, keywords = {Dark matter, Early universe, Galaxy formation, Population III stars, Supermassive black holes, 353, 435, 595, 1285, 1663}, year = {2025}, month = oct, volume = {992}, number = {1}, eid = {136}, pages = {136}, doi = {10.3847/1538-4357/ae061c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...992..136Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, simulation, theory}, month_numeric = {10} }

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Unveiling Extended Components of ’Little Red Dots’ in Rest-Frame Optical

Yiyang Zhang, Xuheng Ding, Lilan Yang, and 26 more authors

arXiv e-prints, Oct 2025

Abs ADS arXiv

Recent JWST observations have revealed a population of red, compact, high-redshift objects called ’Little Red Dots’(LRD), whose host components have remained largely unconstrained, possibly due to their extreme compactness. Current morphological studies have been limited by small samples, as well as by insufficient imaging depth, which may not allow reliable separation between point-like and extended components, leaving the existence and properties of extended components in LRD largely unconstrained. Here, we perform the image stacking analysis of 217 LRDs in four NIRCam bands, representing the largest and homogeneous sample observed from COSMOS-Web survey to date. Our results reveal an unambiguous detection of faint extended emission in the F444W band, with a typical size of \raisebox-0.5ex\textasciitilde200 parsecs and magnitude of \raisebox-0.5ex\textasciitilde27.7 AB at z\raisebox-0.5ex\textasciitilde6.5. We perform four-band photometric SED fitting based on galaxy templates and derive a stellar mass of 8.91+-\raisebox-0.5ex\textasciitilde0.1 logM_sun. Given this stellar mass, the host galaxy is compact, i.e., \raisebox-0.5ex\textasciitilde2.5 times smaller than star-forming populations at similar mass, and the typical black hole mass of LRDs is elevated by \raisebox-0.5ex\textasciitilde1.5 dex above the local MBH-M* relation. This work provides direct observational evidence for the existence of LRD host galaxies and offers crucial insights into the growth of the host galaxy and the co-evolution of galaxies and their black holes within the first billion years after the Big Bang.

@article{2025arXiv251025830Z, author = {{Zhang}, Yiyang and {Ding}, Xuheng and {Yang}, Lilan and {Lambrides}, Erini and {Akins}, Hollis and {Battisti}, Andrew J. and {Casey}, Caitlin M. and {Chen}, Chang-hao and {Cox}, Isa and {Faisst}, Andreas and {Franco}, Maximilien and {Haghjoo}, Aryana and {Ho}, Luis C. and {Inayoshi}, Kohei and {Jin}, Shuowen and {Karmen}, Mitchell and {Koekemoer}, Anton M. and {Kartaltepe}, Jeyhan S. and {Liao}, Kai and {Gozaliasl}, Ghassem and {Onoue}, Masafusa and {Kokorev}, Vasily and {Roy}, Namrata and {Rich}, R. Michael and {Silverman}, John D. and {Tanaka}, Takumi S. and {You}, Bei and {Yesuf}, Hassen M. and {Zavala}, Jorge A.}, title = {{Unveiling Extended Components of 'Little Red Dots' in Rest-Frame Optical}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = oct, eid = {arXiv:2510.25830}, pages = {arXiv:2510.25830}, archiveprefix = {arXiv}, eprint = {2510.25830}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251025830Z}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, photometry, sed}, month_numeric = {10} }

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On the Variability Features of Active Galactic Nuclei in Little Red Dots

Shuying Zhou, Mouyuan Sun, Zijian Zhang, and 2 more authors

The Astrophysical Journal, Oct 2025

Abs DOI ADS

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} }

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The mechanism for creating“dynamical gravastar” black hole mimickers can also explain formation of “little red dots”

Stephen L. Adler

arXiv e-prints, Sep 2025

Abs ADS arXiv

We argue that a high pressure phase transition of relativistic matter to a state with negative energy density, which leads to the formation of horizonless black hole mimickers, can also give rise to the appearance of “little red dots”. The energy source for the dots is the release of latent energy from the phase transition, and their redness is a result of this release taking place in a central region of exponentially small positive g_00, and hence very high gravitational redshift.

@article{2025arXiv250923490A, author = {{Adler}, Stephen L.}, title = {{The mechanism for creating``dynamical gravastar'' black hole mimickers can also explain formation of ``little red dots''}}, journal = {arXiv e-prints}, keywords = {General Relativity and Quantum Cosmology}, year = {2025}, month = sep, eid = {arXiv:2509.23490}, pages = {arXiv:2509.23490}, archiveprefix = {arXiv}, eprint = {2509.23490}, primaryclass = {gr-qc}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250923490A}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, non-agn, spectroscopy, theory}, month_numeric = {9} }

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COSMOS-web: The Overabundance and Physical Nature of “Little Red Dots”—Implications for Early Galaxy and SMBH Assembly

Hollis B. Akins, Caitlin M. Casey, Erini Lambrides, and 38 more authors

The Astrophysical Journal, Sep 2025

Abs DOI ADS

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} }

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Irony at z=6.68: a bright AGN with forbidden Fe emission and multi-component Balmer absorption

Francesco D’Eugenio, Erica Nelson, Xihan Ji, and 11 more authors

arXiv e-prints, Sep 2025

Abs ADS arXiv

We present the deepest medium-resolution JWST/NIRSpec spectroscopy to date of a bright Little Red Dot (LRD) AGN, Irony at z=6.68. The data reveal broad Balmer emission from Hα-Hδ and Balmer absorption in Hα-Hε. The absorption lines are kinematically split: Hα is blueshifted while higher-order lines are redshifted suggesting complex gas kinematics; their relative ratios are inconsistent with a single, passive absorbing screen. The line depths require absorption of both the BLR and the continuum, ruling out a stellar origin, consistent with the smooth Balmer break. We fit the broad Hγ-Hα lines and find the data favor a double-Gaussian effective profile, although exponential wings are evident. Depending on the adopted profile, single-epoch virial estimates give log(M_∙/M_⊙)=7.86-8.39 and λ_\rm Edd=1.7-0.4. The dynamical mass implied by the narrow lines is low log(Mdyn/M_⊙)=9.1, suggesting an overmassive black hole. The narrow lines display little attenuation, A_V<0.5 mag; while broad Hα/Hβ\sim9 and the broad Balmer decrements are inconsistent with standard dust attenuation curves, suggesting collisional processes. The forbidden-line spectrum includes auroral [S II] and [N II], and a forest of [Fe II] lines. Line ratios and kinematics indicate a stratified narrow-line region with both low (n_\rm e=420 cm^-3) and high densities (n_\rm ersim 6.3\times10^5 cm^-3). We detect metal absorption lines in both the optical (Ca II and Na I) and UV range (Fe II UV1-UV3). Our results support a picture of a compact AGN embedded in a dense, high covering-factor and stratified cocoon, with complex neutral-gas kinematics. While the choice of broad-line profile affects the virial estimates of M_∙, we find the effect to be of order 0.6 dex between the different approaches.

@article{2025arXiv251000101D, author = {{D'Eugenio}, Francesco and {Nelson}, Erica and {Ji}, Xihan and {Baggen}, Josephine and {Greene}, Jenny and {Labb{\'e}}, Ivo and {Pezzulli}, Gabriele and {Brown}, Vanessa and {Maiolino}, Roberto and {Matthee}, Jorryt and {Terlevich}, Elena and {Terlevich}, Roberto and {Torralba}, Alberto and {Carniani}, Stefano}, title = {{Irony at z=6.68: a bright AGN with forbidden Fe emission and multi-component Balmer absorption}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2510.00101}, pages = {arXiv:2510.00101}, archiveprefix = {arXiv}, eprint = {2510.00101}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251000101D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, kinematics, spectroscopy}, month_numeric = {9} }

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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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No Luminous Little Red Dots: A Sharp Cutoff in Their Luminosity Function

Yilun Ma, Jenny E. Greene, Marta Volonteri, and 14 more authors

arXiv e-prints, Sep 2025

Abs ADS arXiv

One of the most surprising results of early James Webb Space Telescope (JWST) observations is the discovery of an abundance of red, compact, broad-line objects dubbed “little red dots” (LRDs) at z>4. Their spatial density (\sim10^-4-10^-5\,\mathrmcMpc^-3) is 100 times more abundant than UV-selected quasars at those redshift if one extrapolates the quasar luminosity function (QLF) down to the LRD regime. However, whether LRDs dominate black hole accretion at quasar-like luminosities (L_\mathrmbolrsim 10^45-46\,\mathrmerg s^-1) remains unanswered, as probing the bright end of the LRD luminosity function requires a much larger area than those able to be surveyed by JWST. In this work, we present our search for the brightest LRDs (K<23.7) at 4.5<z<4.9 using wide-area multiwavelength imaging surveys from the near-UV to the infrared bands. With over 15 square degrees of sky coverage, we only identify one single LRD candidate at z_\mathrmphot\approx4.6, which translates into a spatial density of n(M_5100<-23.5)\approx10^-8\,\mathrmcMpc^-3 – this is nearly 10 times less abundant than the UV-selected quasars at similar optical luminosity. When combined with the LRD sample identified by JWST at the same redshift range, we find a sharp cutoff in the optical luminosity function at λL_5100\approx2.5\times10^44\,\mathrmerg s^-1, while the QLF turnover occurs at rsim20 times higher luminosity. We therefore confirm the exclusively low-luminosity nature of LRDs, ruling out that LRDs are the counter parts of quasars. Furthermore, we speculate that, if the shape of the luminosity function holds up, it points to LRDs being powered by low-mass black holes with a narrow range of Eddington-level accretion rates.

@article{2025arXiv250902662M, author = {{Ma}, Yilun and {Greene}, Jenny E. and {Volonteri}, Marta and {Goulding}, Andy D. and {Setton}, David J. and {Annunziatella}, Marianna and {Egami}, Eiichi and {Fan}, Xiaohui and {Kokorev}, Vasily and {Labbe}, Ivo and {Lin}, Xiaojing and {Marchesini}, Danilo and {Matthee}, Jorryt and {Nanayakkara}, Themiya and {Robbins}, Luke and {Sajina}, Anna and {Sawicki}, Marcin}, title = {{No Luminous Little Red Dots: A Sharp Cutoff in Their Luminosity Function}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics}, year = {2025}, month = sep, eid = {arXiv:2509.02662}, pages = {arXiv:2509.02662}, archiveprefix = {arXiv}, eprint = {2509.02662}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250902662M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, multi-wavelength, photometry}, month_numeric = {9} }

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What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?

Krisztina Perger, Judit Fogasy, and Sándor Frey

Universe, Sep 2025

Abs DOI ADS

The real nature of little red dots (LRDs), a class of very compact galaxies in the early Universe recently discovered by the James Webb Space Telescope, is still poorly understood. The most popular theories competing to interpret the phenomena include active galactic nuclei and enhanced star formation in dusty galaxies. To date, however, neither model gives a completely satisfactory explanation to the population as a whole; thus, alternative theories have arisen, including tidal disruption events (TDEs). By considering observational constraints on the radio emission of LRDs, we discuss whether TDEs are adequate alternatives solving these high-redshift enigmas. We utilise radio flux density upper limits from LRD stacking analyses, TDE peak radio luminosities, and volumetric density estimates. We find that the characteristic values of flux densities and luminosities allow radio-quiet TDEs as the underlying process of LRDs in any case, while the less common radio-loud TDEs are compatible with the model under special constraints only. Considering other factors, such as volumetric density estimates, delayed and long-term radio flares of TDEs, and cosmological time dilation, TDEs appear to be a plausible explanation for LRDs from the radio point of view.

@article{2025Univ...11..294P, author = {{Perger}, Krisztina and {Fogasy}, Judit and {Frey}, S{\'a}ndor}, title = {{What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?}}, journal = {Universe}, keywords = {little red dots, tidal disruption events, radio continuum, high redshift}, year = {2025}, month = sep, volume = {11}, number = {9}, eid = {294}, pages = {294}, doi = {10.3390/universe11090294}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025Univ...11..294P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {181048372}, lrdkeys = {early universe, jwst, non-agn, radio, theory}, 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 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}, altmetric = {181615848}, 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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The warm outer layer of a Little Red Dot as the source of [Fe II] and collisional Balmer lines with scattering wings

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

arXiv e-prints, Sep 2025

Abs ADS arXiv

The population of the Little Red Dots (LRDs) may represent a key phase of supermassive black hole (SMBH) growth. A cocoon of dense excited gas is emerging as key component to explain the most striking properties of LRDs, such as strong Balmer breaks and Balmer absorption, as well as the weak IR emission. To dissect the structure of LRDs, we analyze new deep JWST/NIRSpec PRISM and G395H spectra of FRESCO-GN-9771, one of the most luminous known LRDs at z=5.5. These reveal a strong Balmer break, broad Balmer lines and very narrow [O III] emission. We unveil a forest of optical [Fe II] lines, which we argue is emerging from a dense (n_\rm H=10^9-10 cm^-3) warm layer with electron temperature T_\rm e\approx7000 K. The broad wings of Hα and Hβ have an exponential profile due to electron scattering in this same layer. The high \rm Hα:Hβ:Hγ flux ratio of \approx10.4:1:0.14 is an indicator of collisional excitation and resonant scattering dominating the Balmer line emission. A narrow Hγ component, unseen in the other two Balmer lines due to outshining by the broad components, could trace the ISM of a normal host galaxy with a star formation rate \sim5 M_⊙ yr^-1. The warm layer is mostly opaque to Balmer transitions, producing a characteristic P-Cygni profile in the line centers suggesting outflowing motions. This same layer is responsible for shaping the Balmer break. The broad-band spectrum can be reasonably matched by a simple photoionized slab model that dominates the λ>1500 Å continuum and a low mass (\sim10^8 M_⊙) galaxy that could explain the narrow [O III], with only subdominant contribution to the UV continuum. Our findings indicate that Balmer lines are not directly tracing gas kinematics near the SMBH and that the BH mass scale is likely much lower than virial indicators suggest.

@article{2025arXiv251000103T, author = {{Torralba}, Alberto and {Matthee}, Jorryt and {Pezzulli}, Gabriele and {Naidu}, Rohan P. and {Ishikawa}, Yuzo and {Brammer}, Gabriel B. and {Chang}, Seok-Jun and {Chisholm}, John and {de Graaff}, Anna and {D'Eugenio}, Francesco and {Di Cesare}, Claudia and {Eilers}, Anna-Christina and {Greene}, Jenny E. and {Gronke}, Max and {Iani}, Edoardo and {Kokorev}, Vasily and {Kotiwale}, Gauri and {Kramarenko}, Ivan and {Ma}, Yilun and {Mascia}, Sara and {Navarrete}, Benjam{\'\i}n and {Nelson}, Erica and {Oesch}, Pascal and {Simcoe}, Robert A. and {Wuyts}, Stijn}, title = {{The warm outer layer of a Little Red Dot as the source of [Fe II] and collisional Balmer lines with scattering wings}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = sep, eid = {arXiv:2510.00103}, pages = {arXiv:2510.00103}, archiveprefix = {arXiv}, eprint = {2510.00103}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv251000103T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, host galaxy, jwst, spectroscopy}, 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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XMM-Newton Conclusively Identifies an Active Galactic Nucleus in a Green Pea Galaxy

Peter G. Boorman, Jiřı́ Svoboda, Daniel Stern, and 23 more authors

The Astrophysical Journal, Aug 2025

Abs DOI ADS arXiv

Green Pea galaxies are a class of compact, low-mass, low-metallicity star-forming galaxies in the relatively local Universe. They are believed to be analogs of high-redshift galaxies that reionized the Universe, and, indeed, the James Webb Space Telescope (JWST) is now uncovering such populations at record redshifts. Intriguingly, JWST finds evidence suggestive of active galactic nuclei (AGN) in many of these distant galaxies, including the elusive Little Red Dots, which broadly lack any detectable X-ray counterparts. Intuitively, one would expect to detect an AGN in their low-redshift analogs with X-rays, yet no study to date has conclusively identified an X-ray AGN within a Green Pea galaxy. Here we present the deepest X-ray campaign of a Green Pea galaxy performed to date, obtained with the goal of discerning the presence of a (potentially low-luminosity) AGN. The target—SDSS J082247.66+224144.0 (hereafter J0822+2241)—was previously found to display a comparable X-ray spectral shape to more local AGN (\ensuremathΓ \ensuremath∼ 2) and a high luminosity (L_2‑10 keV \ensuremath∼ 10^42 erg s^‑1). We show that over 6.2 yr (rest frame) the 2–10 keV luminosity of J0822+2241 is constant, whereas the soft 0.5–2 keV flux has decreased significantly by \ensuremath∼60%. We discuss possible scenarios to explain the X-ray properties of J0822+2241, finding transient low column density obscuration surrounding an AGN to be the only plausible scenario. J0822+2241 thus provides further evidence that low-luminosity AGN activity could have contributed to the epoch of reionization and that local analogs are useful to derive a complete multiwavelength picture of black hole growth in high-redshift, low-luminosity AGNs. *Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

@article{2025ApJ...988..157B, author = {{Boorman}, Peter G. and {Svoboda}, Ji{\v{r}}{\'\i} and {Stern}, Daniel and {Lehmer}, Bret D. and {Borkar}, Abhijeet and {Brightman}, Murray and {Earnshaw}, Hannah P. and {Harrison}, Fiona A. and {Kouroumpatzakis}, Konstantinos and {Adamcov{\'a}}, Barbora and {Assef}, Roberto J. and {Ehle}, Matthias and {Grefenstette}, Brian and {Grossov{\'a}}, Romana and {Gupta}, Maitrayee and {Kammoun}, Elias and {Kawamuro}, Taiki and {Marcotulli}, Lea and {Miku{\v{s}}incov{\'a}}, Romana and {Middleton}, Matthew J. and {Nathan}, Edward and {Piotrowska}, Joanna M. and {Somalwar}, Jean J. and {Torres-Alb{\`a}}, N{\'u}ria and {Walton}, Dominic J. and {Weisz}, Daniel R.}, title = {{XMM-Newton Conclusively Identifies an Active Galactic Nucleus in a Green Pea Galaxy}}, journal = {\apj}, keywords = {Starburst galaxies, Active galaxies, Compact galaxies, X-ray active galactic nuclei, 1570, 17, 285, 2035}, year = {2025}, month = aug, volume = {988}, number = {2}, eid = {157}, pages = {157}, doi = {10.3847/1538-4357/add727}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...988..157B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {jwst, local counterpart, multi-wavelength, variability, x-ray}, eprint = {2505.08885}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {8} }

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Lonely Little Red Dots: Challenges to the Active Galactic Nucleus Nature of Little Red Dots through Their Clustering and Spectral Energy Distributions

Marı́a Carranza-Escudero, Christopher J. Conselice, Nathan Adams, and 31 more authors

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

Observations with the James Webb Space Telescope reveal a previously unseen population of compact red objects, known as “little red dots” (LRDs). We study a new photometrically selected sample of 124 LRDs in the redshift range z \ensuremath∼ 3–10 selected from Near Infrared Camera coverage of the Cosmic Evolution Early Release Science Survey (CEERS), North Ecliptic Pole Time Domain Field (NEP-TDF), James Webb Space Telescope Advanced Deep Extragalactic Survey (JADES), and JEMS. For JADES, the NEP-TDF, and CEERS, we compare spectral energy distribution (SED) models with and without active galactic nucleus (AGN) components and analyze the impact of an AGN component on the goodness of fit using the Bayesian information criterion (BIC). We find that while the \ensuremathχ^2 of the majority of models containing AGN components is improved compared to models without AGN components, we show that the BIC suggests that models without AGN are a more appropriate fit to LRD SEDs, especially when MIRI data are available. We also measure LRD clustering in the CEERS field, JADES field, and NEP-TDF, where we compare the spatial distribution of LRDs and galaxies with Kolmogorov–Smirnov tests of equality of distribution. We find that the neighbourhood of LRDs tends to be less dense compared to galaxies at all selections and masses and at similar redshifts. We further measure upper limit estimates for the halo masses of LRDs using abundance matching. While the population of LRDs could be a mixture of several different inherent populations, as a whole, it does appear that these systems are mostly hosting compact galaxies or star clusters in formation.

@article{2025ApJ...989L..50C, author = {{Carranza-Escudero}, Mar{\'\i}a and {Conselice}, Christopher J. and {Adams}, Nathan and {Harvey}, Thomas and {Austin}, Duncan and {Behroozi}, Peter and {Ferreira}, Leonardo and {Ormerod}, Katherine and {Duan}, Qiao and {Trussler}, James and {Li}, Qiong and {Westcott}, Lewi and {Windhorst}, Rogier A. and {Coe}, Dan and {Cohen}, Seth H. and {Cheng}, Cheng and {Driver}, Simon P. and {Frye}, Brenda and {Furtak}, Lukas J. and {Grogin}, Norman A. and {Hathi}, Nimish P. and {Jansen}, Rolf A. and {Koekemoer}, Anton M. and {Marshall}, Madeline A. and {O'Brien}, Rosalia and {Pirzkal}, Norbert and {Polletta}, Maria and {Robotham}, Aaron and {Rutkowski}, Michael J. and {Summers}, Jake and {Wilkins}, Stephen M. and {Willmer}, Christopher N. A. and {Yan}, Haojing and {Zitrin}, Adi}, title = {{Lonely Little Red Dots: Challenges to the Active Galactic Nucleus Nature of Little Red Dots through Their Clustering and Spectral Energy Distributions}}, journal = {\apjl}, keywords = {Galaxies, AGN host galaxies, Active galactic nuclei, High-redshift galaxies, James Webb Space Telescope, 573, 2017, 16, 734, 2291}, year = {2025}, month = aug, volume = {989}, number = {2}, eid = {L50}, pages = {L50}, doi = {10.3847/2041-8213/adf73d}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989L..50C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {180488661}, lrdkeys = {clustering, jwst, non-agn, photometry, sed}, eprint = {2506.04004}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {8} }

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The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots

Chang-Hao Chen, Luis C. Ho, Ruancun Li, and 1 more author

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

A significant fraction of little red dots (LRDs) exhibit nearby extended emission of unknown origin. If physically associated with the LRD, this component may trace stellar emission from an off- center host galaxy, neighboring companions, or nebular gas illuminated by the active nucleus. We investigate the detailed spectral energy distribution (SED) of the extended emission near four LRDs in the JWST UNCOVER and MegaScience surveys. We accurately decompose the extended emission from the dominant point source by simultaneously fitting the images in eight broadband and nine medium-band filters. After considering both the results from photometric redshift fitting and the probability of galaxies at different redshifts overlapping, we confirm that the off-center blobs in three sources are physically associated with the LRDs, with two of them showing strong [O III] \ensuremathλ\ensuremathλ4959, 5007 emission captured by the medium-band filters. While the SEDs of all three blobs can be modeled assuming star-forming galaxies with stellar mass \ensuremath∼10^8 M_\ensuremath⊙, the exceptionally strong [O III] emission of two sources is best interpreted as pure nebular emission from low-density (n < 10 cm^‑3), low-metallicity (Z \ensuremath≈ 0.05‑1 Z_\ensuremath⊙) gas photoionized by the ultraviolet radiation from the nearby LRD. Adopting LRD halo masses constrained by clustering measurements and theoretical considerations, we estimate a typical baryonic halo mass accretion rate of \ensuremath∼2‑9 M_\ensuremath⊙ yr^‑1. If the halo accretion rate is sustained to z = 4 and stars form with an efficiency of 10%, the accreted gas would build a galaxy with stellar mass \ensuremath∼10^9 M_\ensuremath⊙, potentially rendering them spatially resolved at lower redshift.

@article{2025ApJ...989L..12C, author = {{Chen}, Chang-Hao and {Ho}, Luis C. and {Li}, Ruancun and {Inayoshi}, Kohei}, title = {{The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots}}, journal = {\apjl}, keywords = {Early universe, High-redshift galaxies, Active galactic nuclei, AGN host galaxies, 435, 734, 16, 2017, Astrophysics of Galaxies}, year = {2025}, month = aug, volume = {989}, number = {1}, eid = {L12}, pages = {L12}, doi = {10.3847/2041-8213/adee0a}, archiveprefix = {arXiv}, eprint = {2505.03183}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989L..12C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {emission lines, host galaxy, jwst, photometry, sed}, month_numeric = {8} }

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Evidence for Evolutionary Pathway-dependent Black Hole Scaling Relations

Jonathan H. Cohn, Emmanuel Durodola, Quinn O. Casey, and 2 more authors

The Astrophysical Journal Letters, Aug 2025

Abs DOI ADS arXiv

Recent observations have identified an abundance of high-redshift active galactic nuclei (AGN) with overmassive supermassive black holes (BHs) compared to the local BH mass‑total stellar mass (M_BH–M_\ensuremath⋆) relation for AGN. High-z M_BH measurements are critical for probing growth histories of BHs and their host galaxies, including BH seeding and evolution of the M_BH–M_\ensuremath⋆ relation. However, BH masses in high-z AGN are generally estimated from single-epoch measurements, which carry large systematic uncertainties. More reliable M_BH detection methods like dynamical measurements are currently only possible in the local Universe or with strongly lensed systems. Fortunately, new dynamical M_BH measurements in a sample of six local galaxies identified as likely relics of common quiescent red nugget galaxies at cosmic noon, as well as a z \ensuremath∼ 2 lensed red nugget, present a complementary probe of high-z relations. We compare the z \ensuremath∼ 2 red nugget and relic BHs to recent results for 4 < z < 11 AGN, quasi-stellar objects, and little red dots. Intriguingly, the z \ensuremath∼ 2 galaxy and local relics all lie on both the local M_BH–M_\ensuremath⋆ relation for bulges and the 4 < z < 7 M_BH–M_\ensuremath⋆ AGN relation, although high-z AGN remain overmassive compared to both local relations. We conclude it is unlikely that a uniform M_BH–M_\ensuremath⋆ redshift evolution applies to all galaxies. Since total M_\ensuremath⋆ is affected by growth processes that may not drive BH growth, different evolutionary pathways must be carefully considered when building BH scaling relations.

@article{2025ApJ...988L..61C, author = {{Cohn}, Jonathan H. and {Durodola}, Emmanuel and {Casey}, Quinn O. and {Lambrides}, Erini and {Hickox}, Ryan C.}, title = {{Evidence for Evolutionary Pathway-dependent Black Hole Scaling Relations}}, journal = {\apjl}, keywords = {High-redshift galaxies, Active galaxies, Early-type galaxies, Active galactic nuclei, Supermassive black holes, Scaling relations, Galaxy evolution, 734, 17, 429, 16, 1663, 2031, 594}, year = {2025}, month = aug, volume = {988}, number = {2}, eid = {L61}, pages = {L61}, doi = {10.3847/2041-8213/adf100}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...988L..61C}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, local counterpart, spectroscopy}, eprint = {2504.00172}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {8} }

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MIDIS: MIRI Uncovers Virgil, the First Little Red Dot with Clear Detection of Its Host Galaxy at z ≃ 6.6

Edoardo Iani, Pierluigi Rinaldi, Karina I. Caputi, and 26 more authors

The Astrophysical Journal, Aug 2025

Abs DOI ADS arXiv

We present Virgil, a Mid-Infrared Instrument (MIRI) extremely red object detected with the F1000W filter as part of the MIRI Deep Imaging Survey observations of the Hubble Ultra Deep Field. Virgil is an Ly\ensuremathα emitter (LAE) at z_spec = 6.6312 \ensuremath\pm 0.0019 (from the Very Large Telescope/MUSE) with a rest-frame UV-to-optical spectral energy distribution (SED) typical of LAEs at similar redshifts. However, MIRI observations reveal an unexpected extremely red color at rest- frame near-infrared (NIR) wavelengths, F444W ‑ F1000W = 2.33 \ensuremath\pm 0.06. Such a steep rise in the NIR, completely missed without MIRI imaging, is poorly reproduced by models including only stellar populations and hints toward the presence of an active galactic nucleus, although alternative explanations such as extreme dust obscuration and strong nebular continuum and emission lines contribution due to young stellar ages cannot be completely ruled out. According to the shape of its overall SED, Virgil belongs to the recently discovered population of little red dots but displays an extended rest- frame UV-optical wavelength morphology following a 2D-Sérsic profile with an average index of n=0.93‑0.31+0.85 and re=0.49‑0.11+0.05 pkpc. Only at MIRI wavelengths, Virgil is unresolved due to the coarser point-spread function. This discovery demonstrates the crucial importance of deep MIRI surveys to reveal the true nature and properties of high-z galaxies that otherwise would be misinterpreted and raises the question of how common Virgil-like objects could be in the early Universe.

@article{2025ApJ...989..160I, author = {{Iani}, Edoardo and {Rinaldi}, Pierluigi and {Caputi}, Karina I. and {Annunziatella}, Marianna and {Langeroodi}, Danial and {Melinder}, Jens and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {{\'A}lvarez-M{\'a}rquez}, Javier and {Boogaard}, Leindert A. and {Bosman}, Sarah E. I. and {Costantin}, Luca and {Moutard}, Thibaud and {Colina}, Luis and {{\"O}stlin}, G{\"o}ran and {Greve}, Thomas R. and {Wright}, Gillian and {Alonso-Herrero}, Almudena and {Bik}, Arjan and {Gillman}, Steven and {Crespo G{\'o}mez}, Alejandro and {Hjorth}, Jens and {Kendrew}, Sarah and {Labiano}, Alvaro and {Pye}, John P. and {Tikkanen}, Tuomo V. and {Walter}, Fabian and {G{\"u}del}, Manuel and {Henning}, Thomas and {van der Werf}, Paul P.}, title = {{MIDIS: MIRI Uncovers Virgil, the First Little Red Dot with Clear Detection of Its Host Galaxy at z ≃ 6.6}}, journal = {\apj}, keywords = {Galaxy formation, Galaxy evolution, High-redshift galaxies, Stellar populations, Active galactic nuclei, Galaxy ages, James Webb Space Telescope, 595, 594, 734, 1622, 16, 576, 2291, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = aug, volume = {989}, number = {2}, eid = {160}, pages = {160}, doi = {10.3847/1538-4357/ade5a6}, archiveprefix = {arXiv}, eprint = {2406.18207}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...989..160I}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, host galaxy, jwst, morphology, sed}, month_numeric = {8} }

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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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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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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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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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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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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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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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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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Exploring the Active Galactic Nucleus Fraction of a Sample of JWST’s Little Red Dots at 4 < z < 8: Overmassive Black Holes Are Strongly Favored

Emmanuel Durodola, Fabio Pacucci, and Ryan C. Hickox

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

JWST is revolutionizing our view of the early Universe by pushing the boundaries of detectable galaxies and black holes in redshift (upward) and mass (downward). The little red dots (LRDs), detected by several surveys at z > 4, present a significant interpretational challenge, as their spectral energy distributions (SEDs) can mimic both active galactic nucleus (AGN) and stellar population templates. This study analyzes 19 LRDs from the JWST Advanced Deep Extragalactic Survey survey, utilizing NIRCam and MIRI photometry. By performing SED fitting across a vast parameter space, we explore a broad range of AGN fractions, defined as the ratio of the monochromatic luminosities (AGN, galaxy, and dust) over a specified wavelength range, 0.4–0.7 \ensuremathμm rest frame. We find that 17 of the 19 LRDs investigated are consistent with having significant AGN contributions, with best-fitting AGN fractions ranging between 20% and 70%, while one galaxy shows a low AGN contribution (2%) and another appears to be purely star forming. Moreover, assuming these LRDs do indeed host AGN, we can place limits on their black hole masses using the inferred AGN bolometric luminosities and adopting the Eddington limit. We find that, independent of the specific AGN fraction adopted, the LRDs’ black holes are significantly overmassive relative to their host galaxies—by \ensuremath∼1 dex, and up to \ensuremath∼4 dex in the most extreme cases—compared to the local M_•–M_\ensuremath⋆ relation. The presence of overmassive black holes in the high-z Universe may provide the strongest evidence yet of heavy black hole seeding occurring during the cosmic dark ages.

@article{2025ApJ...985..169D, author = {{Durodola}, Emmanuel and {Pacucci}, Fabio and {Hickox}, Ryan C.}, title = {{Exploring the Active Galactic Nucleus Fraction of a Sample of JWST's Little Red Dots at 4 < z < 8: Overmassive Black Holes Are Strongly Favored}}, journal = {\apj}, keywords = {Active galaxies, Supermassive black holes, Galaxy evolution, High-redshift galaxies, Scaling relations, 17, 1663, 594, 734, 2031}, year = {2025}, month = jun, volume = {985}, number = {2}, eid = {169}, pages = {169}, doi = {10.3847/1538-4357/adced2}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...985..169D}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {164629402}, lrdkeys = {black hole mass, early universe, jwst, photometry, sed}, eprint = {2406.10329}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Dark Bondi Accretion Aided by Baryons and the Origin of JWST Little Red Dots

Wei-Xiang Feng, Hai-Bo Yu, and Yi-Ming Zhong

arXiv e-prints, Jun 2025

Abs ADS arXiv

The gravothermal core collapse of self-interacting dark matter halos provides a compelling mechanism for seeding supermassive black holes in the early Universe. In this scenario, a small fraction of a halo, approximately 1% of its mass, collapses into a dense core, which could further evolve into a black hole. We demonstrate that this process can account for the origin of JWST little red dots (LRDs) observed at redshifts z\sim4-11, where black holes with masses of 10^7\rm M_⊙ can form within 500\rm Myr after the formation of host halos with masses of 10^9\rm M_⊙. Even if the initial collapse region triggering general-relativistic instability has a mass on the order of one solar mass, the resulting seed can grow into an intermediate-mass black hole via Eddington accretion of baryonic gas. Subsequently, it can continue to grow into a supermassive black hole through dark Bondi accretion of dark matter particles. In this scenario, the majority of the black hole’s mass originates from dark matter accretion rather than baryonic matter, naturally explaining the overmassive feature of LRDs.

@article{2025arXiv250617641F, author = {{Feng}, Wei-Xiang and {Yu}, Hai-Bo and {Zhong}, Yi-Ming}, title = {{Dark Bondi Accretion Aided by Baryons and the Origin of JWST Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies, Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology}, year = {2025}, month = jun, eid = {arXiv:2506.17641}, pages = {arXiv:2506.17641}, archiveprefix = {arXiv}, eprint = {2506.17641}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250617641F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, jwst, theory}, month_numeric = {6} }

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Investigating photometric and spectroscopic variability in the multiply imaged little red dot A2744-QSO1

Lukas J. Furtak, Amy R. Secunda, Jenny E. Greene, and 25 more authors

Astronomy & Astrophysics, Jun 2025

Abs DOI ADS arXiv

JWST observations have uncovered a new population of red, compact objects at high redshifts dubbed “little red dots” (LRDs), which typically show broad emission lines and are thought to be dusty active galactic nuclei (AGNs). Some of their other features, however, challenge the AGN explanation, such as prominent Balmer breaks and extremely faint or even missing metal high-ionization lines, X-ray, or radio emission, including in deep stacks. Time variability is another robust test of AGN activity. Here, we exploit the z = 7.045 multiply imaged LRD A2744-QSO1, which offers a particularly unique test of variability due to lensing-induced time delays between the three images spanning 22 yr (2.7 yr in the rest-frame), to investigate its photometric and spectroscopic variability. We find the equivalent widths (EWs) of the broad H\ensuremathα and H\ensuremathβ lines, which are independent of magnification and other systematics, to exhibit significant variations, of up to 18 \ensuremath\pm 3% for H\ensuremathα and up to 22 \ensuremath\pm 8% in H\ensuremathβ, on a timescale of 875 d (2.4 yr) in the rest-frame. This suggests that A2744-QSO1 is indeed an AGN. We find no significant photometric variability beyond the limiting systematic uncertainties, so it currently cannot be determined whether the EW variations are due to line-flux or continuum variability. These results are consistent with a typical damped random walk variability model for an AGN such as A2744-QSO1 (M_BH = 4 \texttimes 10^7 M_\ensuremath⊙) given the sparse sampling of the light curve with the available data. Our results therefore support the AGN interpretation of this LRD, and highlight the need for further photometric and spectroscopic monitoring in order to build a detailed and reliable light curve.

@article{2025A&A...698A.227F, author = {{Furtak}, Lukas J. and {Secunda}, Amy R. and {Greene}, Jenny E. and {Zitrin}, Adi and {Labb{\'e}}, Ivo and {Golubchik}, Miriam and {Bezanson}, Rachel and {Kokorev}, Vasily and {Atek}, Hakim and {Brammer}, Gabriel B. and {Chemerynska}, Iryna and {Cutler}, Sam E. and {Dayal}, Pratika and {Feldmann}, Robert and {Fujimoto}, Seiji and {Glazebrook}, Karl and {Leja}, Joel and {Ma}, Yilun and {Matthee}, Jorryt and {Naidu}, Rohan P. and {Nelson}, Erica J. and {Oesch}, Pascal A. and {Pan}, Richard and {Price}, Sedona H. and {Suess}, Katherine A. and {Wang}, Bingjie and {Weaver}, John R. and {Whitaker}, Katherine E.}, title = {{Investigating photometric and spectroscopic variability in the multiply imaged little red dot A2744-QSO1}}, journal = {\aap}, keywords = {gravitational lensing: strong, galaxies: high-redshift, quasars: emission lines, quasars: supermassive black holes, quasars: individual: A2744-QSO1}, year = {2025}, month = jun, volume = {698}, eid = {A227}, pages = {A227}, doi = {10.1051/0004-6361/202554110}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...698A.227F}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, emission lines, jwst, spectroscopy, variability}, altmetric = {174139057}, eprint = {2502.07875}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Another Piece to the Puzzle: Radio Detection of a JWST-detected Active Galactic Nucleus Candidate

Anniek J. Gloudemans, Kenneth J. Duncan, Anna-Christina Eilers, and 5 more authors

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

Radio observations can provide crucial insight into the nature of a new abundant and mysterious population of dust-reddened active galactic nuclei (AGN) candidates discovered by the James Webb Space Telescope (JWST), including “Little Red Dots.” In this study, we search for radio bright sources in a large sample of \ensuremath∼700 JWST-discovered AGN candidates (z \ensuremath∼ 2–11) in the 0.144–3 GHz frequency range, utilizing deep radio imaging in the Cosmic Evolution Survey and Great Observatories Origins Deep Survey North and South. Only one source, PRIMER-COS 3866 at z = 4.66, is significantly detected in our radio surveys, which has been previously identified as an X-ray AGN. Its radio properties are consistent with both an AGN and star formation origin with a spectral index of \ensuremat hα=‑0 .76‑0.09+0.11 , radio-loudness of R \ensuremath≈ 0.5, and brightness temperature limit of T_b \ensuremath≳ 10^3 K. Our stacking results of both spectroscopically and photometrically selected AGN candidates yield nondetections in all fields, with 3\ensuremathσ limits of L_1.4 GHz < 8.6 \texttimes 10^39 erg s^‑1 (spectroscopic sample) and L_1.3 GHz < 1.3 \texttimes 10^39 erg s^‑1 (photometric sample). We demonstrate that these results are still consistent with expectations from the empirical L_X–L_H\ensuremathα and L_X–L_R correlations established for local AGN. We argue that current radio observations in these studied fields have insufficient depth to claim JWST-discovered AGN candidates are radio weak. We project that future surveys carried out by the Square Kilometer Array and Next Generation Very Large Array should be able to obtain significant detections within a few hours, providing crucial measurements of their brightness temperature, which would allow for distinguishing between AGN and starburst-driven origins of this new abundant population.

@article{2025ApJ...986..130G, author = {{Gloudemans}, Anniek J. and {Duncan}, Kenneth J. and {Eilers}, Anna-Christina and {Farina}, Emanuele Paolo and {Harikane}, Yuichi and {Inayoshi}, Kohei and {Lambrides}, Erini and {Vardoulaki}, Eleni}, title = {{Another Piece to the Puzzle: Radio Detection of a JWST-detected Active Galactic Nucleus Candidate}}, journal = {\apj}, keywords = {High-redshift galaxies, Radio continuum emission, Active galactic nuclei, James Webb Space Telescope, 734, 1340, 16, 2291}, year = {2025}, month = jun, volume = {986}, number = {2}, eid = {130}, pages = {130}, doi = {10.3847/1538-4357/adddb9}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986..130G}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {dust, jwst, multi-wavelength, radio, x-ray}, altmetric = {172893653}, eprint = {2501.04912}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Where Have All the Little Red Dots Gone? Supermassive Black Hole Binary Dynamics and Its Impact on Galaxy Properties

Fazeel Mahmood Khan, Benjamin L. Davis, Andrea Valerio Macciò, and 1 more author

The Astrophysical Journal Letters, Jun 2025

Abs DOI ADS arXiv

Recent James Webb Space Telescope observations have revealed a peculiar class of galaxies at redshifts z \ensuremath≳ 6, characterized by extremely high central stellar densities and overmassive central supermassive black holes (SMBHs), “little red dots” (LRDs). A critical question remains: if LRDs were common at high redshifts, how would they evolve into local elliptical galaxies with significantly lower central densities? To address this, we performed direct N-body simulations of LRD mergers, focusing on the coevolution of host galaxies and central SMBHs. We track the complete evolution of SMBH binaries into the three-body hardening and gravitational-wave (GW) emission phase. Our results demonstrate that during galaxy mergers, the central SMBHs can eject a substantial amount of mass from the galactic core via the three-body slingshot effect, leading to a decrease in central stellar surface density by an order of magnitude. Additionally, GW recoil can further contribute in making the galaxy centers less dense and more in alignment with low-redshift quiescent galaxies. This transformation occurs on a relatively short timescale of a few \ensuremath∼100 Myr, implying that LRDs can evolve into lower-redshift elliptical galaxies by z < 4. The timescales for our SMBH mergers vary between 100 and 800 Myr, depending on the initial orbital parameters of the merging galaxies and the mass ratio of the SMBHs. Our findings provide a plausible mechanism for the transformation of LRDs into elliptical galaxies while highlighting the efficiency of SMBH mergers in such high-density environments, which plays a crucial role in SMBH growth.

@article{2025ApJ...986L...1K, author = {{Khan}, Fazeel Mahmood and {Davis}, Benjamin L. and {Macci{\`o}}, Andrea Valerio and {Holley-Bockelmann}, Kelly}, title = {{Where Have All the Little Red Dots Gone? Supermassive Black Hole Binary Dynamics and Its Impact on Galaxy Properties}}, journal = {\apjl}, keywords = {Black hole physics, 159}, year = {2025}, month = jun, volume = {986}, number = {1}, eid = {L1}, pages = {L1}, doi = {10.3847/2041-8213/adda4c}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986L...1K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, host galaxy, jwst, simulation, theory}, altmetric = {175093686}, eprint = {2503.07711}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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The Rise of Faint, Red Active Galactic Nuclei at z > 4: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields

Dale D. Kocevski, Steven L. Finkelstein, Guillermo Barro, and 54 more authors

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

We present a sample of 341 “little red dots” (LRDs) spanning the redshift range z \ensuremath∼ 2–11 using data from the CEERS, PRIMER, JADES, UNCOVER, and NGDEEP surveys. Unlike past use of color indices to identify LRDs, we employ continuum slope fitting using shifting bandpasses to sample the same rest-frame emission blueward and redward of the Balmer break. This enables the detection of LRDs over a wider redshift range and with less contamination from galaxies with strong breaks that otherwise lack a rising red continuum. The redshift distribution of our sample increases at z log(NH/cm2 ) of 23. 3‑1.3+0.4 and 22. 72‑0.16+0.13 . Our analysis reveals that reddened AGN emission dominates their rest-optical light, while the rest-UV originates from their host galaxies. We also present NIRSpec observations from the RUBIES survey of 17 LRDs that show broad emission lines consistent with AGN activity. The confirmed AGN fraction of our sample is 71% for sources with F444W < 26.5. In addition, we find three LRDs with blueshifted Balmer absorption features in their spectra, suggesting an outflow of high-density, low-ionization gas from near the central engine of these faint, red AGN.

@article{2025ApJ...986..126K, author = {{Kocevski}, Dale D. and {Finkelstein}, Steven L. and {Barro}, Guillermo and {Taylor}, Anthony J. and {Calabr{\`o}}, Antonello and {Laloux}, Brivael and {Buchner}, Johannes and {Trump}, Jonathan R. and {Leung}, Gene C. K. and {Yang}, Guang and {Dickinson}, Mark and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Pacucci}, Fabio and {Inayoshi}, Kohei and {Somerville}, Rachel S. and {McGrath}, Elizabeth J. and {Akins}, Hollis B. and {Bagley}, Micaela B. and {Bowler}, Rebecca A. A. and {Bisigello}, Laura and {Carnall}, Adam and {Casey}, Caitlin M. and {Cheng}, Yingjie and {Cleri}, Nikko J. and {Costantin}, Luca and {Cullen}, Fergus and {Davis}, Kelcey and {Donnan}, Callum T. and {Dunlop}, James S. and {Ellis}, Richard S. and {Ferguson}, Henry C. and {Fujimoto}, Seiji and {Fontana}, Adriano and {Giavalisco}, Mauro and {Grazian}, Andrea and {Grogin}, Norman A. and {Hathi}, Nimish P. and {Hirschmann}, Michaela and {Huertas-Company}, Marc and {Holwerda}, Benne W. and {Illingworth}, Garth and {Juneau}, St{\'e}phanie and {Kartaltepe}, Jeyhan S. and {Koekemoer}, Anton M. and {Li}, Wenxiu and {Lucas}, Ray A. and {Magee}, Dan and {Mason}, Charlotte and {McLeod}, Derek J. and {McLure}, Ross J. and {Napolitano}, Lorenzo and {Papovich}, Casey and {Pirzkal}, Nor and {Rodighiero}, Giulia and {Santini}, Paola and {Wilkins}, Stephen M. and {Yung}, L. Y. Aaron}, title = {{The Rise of Faint, Red Active Galactic Nuclei at z > 4: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields}}, journal = {\apj}, keywords = {Active galactic nuclei, Supermassive black holes, 16, 1663}, year = {2025}, month = jun, volume = {986}, number = {2}, eid = {126}, pages = {126}, doi = {10.3847/1538-4357/adbc7d}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986..126K}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {early universe, jwst, spectroscopy, x-ray}, altmetric = {178125502}, eprint = {2404.03576}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Black Holes in the Red-sequence Elliptical Galaxies at Redshifts ∼0.7-2.5: Not Dark Energy Source but Remanants of Little Red Dots

Lei Lei, Ze-Fan Wang, Yi-Ying Wang, and 2 more authors

arXiv e-prints, Jun 2025

Abs ADS arXiv

The nature of dark energy remains one of the most profound mysteries in modern cosmology. One intriguing proposal is that black holes (BHs) could be the astrophysical source of dark energy through a cosmological coupling mechanism, and strong evidence has been claimed via analyzing the growth of the black hole masses in the red-sequence elliptical galaxies at redshifts ≤2.5. In this work, with a group of very high redshift AGNs detected by the James Webb Space Telescope (JWST) in the red-sequence elliptical galaxies, we show that the possibility of BHs being the astrophysical source of dark energy has been rejected at a confidence level exceeding 10σ. Moreover, it turns out that the Little Red Dots recently discovered by JWST, characterized by the low accretion rates, can naturally evolve into the red- sequence elliptical galaxies hosting the relatively low mass black holes at the redshifts of ∼0.7-2.5, without the need of black hole cosmological coupling.

@article{2025arXiv250619589L, author = {{Lei}, Lei and {Wang}, Ze-Fan and {Wang}, Yi-Ying and {Feng}, Lei and {Fan}, Yi-Zhong}, title = {{Black Holes in the Red-sequence Elliptical Galaxies at Redshifts $\sim 0.7-2.5$: Not Dark Energy Source but Remanants of Little Red Dots}}, journal = {arXiv e-prints}, keywords = {Cosmology and Nongalactic Astrophysics, Astrophysics of Galaxies, High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology}, year = {2025}, month = jun, eid = {arXiv:2506.19589}, pages = {arXiv:2506.19589}, archiveprefix = {arXiv}, eprint = {2506.19589}, primaryclass = {astro-ph.CO}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250619589L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, host galaxy, jwst, non-agn}, month_numeric = {6} }

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Possible environmental quenching in an interacting little red dot pair at z \ensuremath∼ 7

Rosa M. Mérida, Gaia Gaspar, Marcin Sawicki, and 14 more authors

Astronomy & Astrophysics, Jun 2025

Abs DOI ADS arXiv

We report the discovery of a z \ensuremath∼ 7 group of galaxies that contains two little red dots (LRDs) just 3.3 kpc apart, along with three potential satellite galaxies, as part of the Canadian NIRISS Unbiased Cluster Survey (CANUCS). The spectral energy distributions (SEDs) of this LRD pair show evidence of a Balmer break, consistent with a recent (\ensuremath∼100 Myr) quenching of star formation. In contrast, the satellites are compatible with a recent-onset (\ensuremath∼100 Myr), ongoing burst of star formation. LRD1’s SED is consistent with a dust-free active galactic nucleus (AGN) being the source of the UV excess in the galaxy. The optical continuum would be powered by the emission from an obscured post-starburst and the AGN at a subdominant level. LRD2’s SED is more ambiguous, but it could also be indicative of a dust-free AGN. In this scenario, these LRDs would be massive (M_\ensuremath⋆ \ensuremath∼ 10^10 M_\ensuremath⊙) and dusty (A(V) > 1 mag) and the three satellites would be lower- mass objects (M_\ensuremath⋆ \ensuremath∼ 10^8 ‑ 9 M_\ensuremath⊙) subject to low dust attenuations. The proximity of the two LRDs suggests that their interaction is responsible for their recent star formation histories, which can be interpreted as environmental bursting and quenching in the epoch of reionization.

@article{2025A&A...698A.317M, author = {{M{\'e}rida}, Rosa M. and {Gaspar}, Gaia and {Sawicki}, Marcin and {Asada}, Yoshihisa and {Desprez}, Guillaume and {Rihtar{\v{s}}i{\v{c}}}, Gregor and {Antwi-Danso}, Jacqueline and {Tripodi}, Roberta and {Willott}, Chris J. and {Brada{\v{c}}}, Maru{\v{s}}a and {Brammer}, Gabriel B. and {Iyer}, Kartheik G. and {Martis}, Nicholas S. and {Muzzin}, Adam and {Noirot}, Ga{\"e}l and {Sarrouh}, Ghassan T. E. and {Markov}, Vladan}, title = {{Possible environmental quenching in an interacting little red dot pair at z {\ensuremath{\sim}} 7}}, journal = {\aap}, keywords = {galaxies: active, galaxies: evolution, galaxies: high-redshift, galaxies: interactions}, year = {2025}, month = jun, volume = {698}, eid = {A317}, pages = {A317}, doi = {10.1051/0004-6361/202553943}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...698A.317M}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {173648133}, lrdkeys = {clustering, dust, early universe, sed, starburst}, eprint = {2501.17925}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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A little red dot up close

Lindsay Oldham

Nature Astronomy, Jun 2025

DOI ADS

@article{2025NatAs...9..776O, author = {{Oldham}, Lindsay}, title = {{A little red dot up close}}, journal = {Nature Astronomy}, year = {2025}, month = jun, volume = {9}, pages = {776-776}, doi = {10.1038/s41550-025-02599-3}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025NatAs...9..776O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {178218301}, lrdkeys = {case study, dust, non-agn, sed, starburst}, month_numeric = {6} }

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The VLA Frontier Fields Survey: A 6GHz High-resolution Radio Survey of Abell 2744

Esteban A. Orozco, Eric F. Jiménez-Andrade, Eric J. Murphy, and 5 more authors

arXiv e-prints, Jun 2025

Abs ADS arXiv

We present a 6GHz radio continuum image of the galaxy cluster Abell 2744 (z = 0.307) obtained with the Karl G. Jansky Very Large Array (VLA) as part of the VLA Frontier Fields program, whose goal is to explore the radio continuum emission from high-redshift galaxies that are magnified by foreground, massive galaxy clusters. With an rms noise of ≈1 μJy beam^-1, at the phase center, and sub-arcsec angular resolution (θ_1/2=0.82 arcsec), this is the deepest and most detailed radio image of Abell 2744 ever obtained. A total of 93 sources are detected with a peak signal-to-noise ratio \geq5, of which 46 have optical/near-infrared (IR) counterparts with available redshift, magnification (μ), and stellar mass (M_*) estimates. The radio sources are distributed over a redshift from 0.15 to 3.55, with a median redshift value of z = 0.93, and a median stellar mass of M_*= 2.3 \times 10^10\,\rmM_⊙. A comparison between the radio-based star formation rates (SFRs) and those derived from ultraviolet- to-near IR data reveals that the radio SFRs are, on average, an order of magnitude higher than the ultraviolet-to-near IR SFRs. We look for radio counterparts of the so-called “Little Red Dots (LRDs)” galaxies at z\approx6 in Abell 2744, but find no significant detections. After stacking, we derive a 3σ upper limit to the 6GHz radio luminosity of LRDs of 4.1\times 10^39\,\rm erg s^-1. Finally, we present a sample of 22 moderately/strongly lensed galaxies (μrsim 2) in the VLA Frontier Fields survey, which is adequate to zoom into star formation processes of main sequence galaxies at z≈1-2.

@article{2025arXiv250620634O, author = {{Orozco}, Esteban A. and {Jim{\'e}nez-Andrade}, Eric F. and {Murphy}, Eric J. and {Smail}, Ian and {Momjian}, Emmanuel and {Heywood}, Ian and {Vega-Gutierrez}, Miguel and {DeCoursey}, Christa}, title = {{The VLA Frontier Fields Survey: A 6GHz High-resolution Radio Survey of Abell 2744}}, journal = {arXiv e-prints}, keywords = {Astrophysics of Galaxies}, year = {2025}, month = jun, eid = {arXiv:2506.20634}, pages = {arXiv:2506.20634}, archiveprefix = {arXiv}, eprint = {2506.20634}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025arXiv250620634O}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {multi-wavelength, non-jwst, photometry, radio, starburst}, month_numeric = {6} }

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’Little red dots’ cannot reside in the same dark matter haloes as comparably luminous unobscured quasars

Elia Pizzati, Joseph F. Hennawi, Joop Schaye, and 4 more authors

Monthly Notices of the Royal Astronomical Society, Jun 2025

Abs DOI ADS arXiv

The JWST has uncovered a new population of candidate broad-line active galactic nucleus (AGN) emerging in the early Universe, named ’little red dots’ (LRDs) because of their compactness and red colours at optical wavelengths. LRDs appear to be surprisingly abundant (≈ 10^-5  \rm cMpc^-3) given that their inferred bolometric luminosities largely overlap with those of the ultraviolet (UV)-luminous quasars identified at high z in wide-field spectroscopic surveys. In this work, we investigate how the population of LRDs and/or other UV-obscured AGN relates to the one of unobscured, UV-selected quasars. By comparing their number densities, we infer an extremely large and rapidly evolving obscured:unobscured ratio, ranging from ≈ 20:1 at z≈4 to ≈ 2300:1 at z≈7, and possibly extending out to very high (≈ 10^47 \rm erg \rm s^-1) bolometric luminosities. This large obscured:unobscured ratio is incompatible with the UV-luminous duty cycle measured for unobscured quasars at z≈4\!-\!6, suggesting that LRDs are too abundant to be hosted by the same haloes as unobscured quasars. This implies that either (a) the bolometric luminosities of LRDs are strongly overestimated or (b) LRDs follow different scaling relations than those of UV-selected quasars, representing a new population of accreting supermassive black holes emerging in the early Universe. A direct comparison between the clustering of LRDs and that of faint UV-selected quasars will ultimately confirm these findings and shed light on key properties of LRDs such as their host mass distribution and duty cycle. We provide a mock analysis for the clustering of LRDs and show that it is feasible with current and upcoming JWST surveys.

@article{2025MNRAS.539.2910P, author = {{Pizzati}, Elia and {Hennawi}, Joseph F. and {Schaye}, Joop and {Eilers}, Anna-Christina and {Huang}, Jiamu and {Schindler}, Jan-Torge and {Wang}, Feige}, title = {{'Little red dots' cannot reside in the same dark matter haloes as comparably luminous unobscured quasars}}, journal = {\mnras}, keywords = {galaxies: high-redshift, quasars: general, quasars: supermassive black holes, large-scale structure of Universe}, year = {2025}, month = jun, volume = {539}, number = {4}, pages = {2910-2925}, doi = {10.1093/mnras/staf660}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025MNRAS.539.2910P}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, altmetric = {168768628}, lrdkeys = {black hole mass, clustering, dust, early universe, jwst}, eprint = {2409.18208}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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Broad-line AGNs at 3.5 < z < 6: The Black Hole Mass Function and a Connection with Little Red Dots

Anthony J. Taylor, Steven L. Finkelstein, Dale D. Kocevski, and 48 more authors

The Astrophysical Journal, Jun 2025

Abs DOI ADS arXiv

We present a sample of 62 H\ensuremathα detected broad-line active galactic nuclei (BLAGNs) at redshifts 3.5 0), independent of contributions from emission lines to the broadband photometry. We construct the black hole (BH) mass function at 3.5 < z < 6 after computing robust completeness corrections. This BH mass function shows agreement with recent JWST-based BH mass functions, though we extend these earlier results to log (M_BH/M_\ensuremath⊙) < 7. The derived BH mass function is consistent with theoretical models, indicating that the observed abundance of BHs in the early Universe may not be discrepant with physically motivated predictions. The BH mass function shape resembles a largely featureless power law, suggesting that signatures from BH seeding have been lost by redshift z \ensuremath∼ 5–6. Finally, we compute the BLAGN UV luminosity function and find agreement with JWST-detected BLAGN samples from recent works, finding that BLAGN hosts constitute \ensuremath≲10% of the total observed UV luminosity at all but the brightest luminosities.

@article{2025ApJ...986..165T, author = {{Taylor}, Anthony J. and {Finkelstein}, Steven L. and {Kocevski}, Dale D. and {Jeon}, Junehyoung and {Bromm}, Volker and {Amor{\'\i}n}, Ricardo O. and {Arrabal Haro}, Pablo and {Backhaus}, Bren E. and {Bagley}, Micaela B. and {Banados}, Eduardo and {Bhatawdekar}, Rachana and {Brooks}, Madisyn and {Calabr{\`o}}, Antonello and {Ortiz}, {\'O}scar A. Ch{\'a}vez and {Cheng}, Yingjie and {Cleri}, Nikko J. and {Cole}, Justin W. and {Davis}, Kelcey and {Dickinson}, Mark and {Donnan}, Callum and {Dunlop}, James S. and {Ellis}, Richard S. and {Fern{\'a}ndez}, Vital and {Fontana}, Adriano and {Fujimoto}, Seiji and {Giavalisco}, Mauro and {Grazian}, Andrea and {Guo}, Jingsong and {Hathi}, Nimish P. and {Holwerda}, Benne W. and {Hirschmann}, Michaela and {Inayoshi}, Kohei and {Kartaltepe}, Jeyhan S. and {Khusanova}, Yana and {Koekemoer}, Anton M. and {Kokorev}, Vasily and {Larson}, Rebecca L. and {Leung}, Gene C. K. and {Lucas}, Ray A. and {McLeod}, Derek J. and {Napolitano}, Lorenzo and {Onoue}, Masafusa and {Pacucci}, Fabio and {Papovich}, Casey and {P{\'e}rez-Gonz{\'a}lez}, Pablo G. and {Pirzkal}, Nor and {Somerville}, Rachel S. and {Trump}, Jonathan R. and {Wilkins}, Stephen M. and {Yung}, L. Y. Aaron and {Zhang}, Haowen}, title = {{Broad-line AGNs at 3.5 < z < 6: The Black Hole Mass Function and a Connection with Little Red Dots}}, journal = {\apj}, keywords = {Supermassive black holes, Quasars, Active galactic nuclei, Broad band photometry, High-redshift galaxy clusters, High-redshift galaxies, Astrophysical black holes, Black holes, 1663, 1319, 16, 184, 2007, 734, 98, 162}, year = {2025}, month = jun, volume = {986}, number = {2}, eid = {165}, pages = {165}, doi = {10.3847/1538-4357/add15b}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025ApJ...986..165T}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, emission lines, jwst, spectroscopy}, eprint = {2409.06772}, archiveprefix = {arXiv}, primaryclass = {astro-ph.GA}, month_numeric = {6} }

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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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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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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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“In Brief: ”“Little Red Dots”“ and Early Black Holes”

Hannah Richter

\skytel, May 2025

ADS

@article{2025S&T...149e...9R, author = {{Richter}, Hannah}, title = {{``In Brief: ''``Little Red Dots''`` and Early Black Holes''}}, journal = {\skytel}, year = {2025}, month = may, volume = {149}, number = {5}, pages = {9}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025S\&T...149e...9R}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, early universe, multi-wavelength, non-agn, theory}, month_numeric = {5} }

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Suppressed Accretion onto Massive Black Hole Binaries Surrounded by Thin Disks

Christopher Tiede, Jonathan Zrake, Andrew MacFadyen, and 1 more author

The Astrophysical Journal, May 2025

Abs DOI ADS arXiv

We demonstrate that gas disks around binary systems might deliver gas to the binary components only when the circumbinary disk is relatively warm. We present new grid-based hydrodynamics simulations, performed with the binary on the grid and a locally isothermal equation of state, in which the binary is seen to functionally “stop accreting” if the orbital Mach number in the disk exceeds a threshold value of about 40. Above this threshold, the disk continues to extract angular momentum from the binary orbit, but it delivers very little mass to the black holes and instead piles up mass in a ring surrounding the binary. This ring will eventually become viscously relaxed and deliver mass to the binary at the large-scale inflow rate. However, we show that the timescale for such relaxation can far exceed the implied binary lifetime. We demonstrate that the ability of a binary–disk system to equilibrate is dependent on the efficiency at which accretion streams deposit mass onto the binary, which, in turn is highly sensitive to the thermodynamic conditions of the inner disk. If disks around massive black hole binaries do operate in such nonaccreting regimes, it suggests these systems may be dimmer than their single black hole counterparts but could exhibit dramatic rebrightening after the black holes inspiral and merge. This dimming begins in the UV/optical and could completely choke high-energy emission, such that these systems would likely be intrinsically X-ray weak with reddened continua, potentially resembling the spectra of “little red dots” recently identified in JWST observations.

@article{2025ApJ...984..144T, author = {{Tiede}, Christopher and {Zrake}, Jonathan and {MacFadyen}, Andrew and {Haiman}, Zolt{\'a}n}, title = {{Suppressed Accretion onto Massive Black Hole Binaries Surrounded by Thin Disks}}, journal = {\apj}, keywords = {Accretion, Active galactic nuclei, Hydrodynamical simulations, Supermassive black holes, 14, 16, 767, 1663}, 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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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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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, host galaxy, jwst, non-agn, 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, jwst, sed, spectroscopy}, month_numeric = {3} }

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Exploring active galactic nuclei and little red dots with the Obelisk simulation

M. Volonteri, M. Trebitsch, J. E. Greene, and 8 more authors

Astronomy & Astrophysics, Mar 2025

Abs DOI ADS arXiv

The James Webb Space telescope has discovered an abundant population of broad line emitters, typical signposts for Active Galactic Nuclei (AGN). Many of these sources have red colors and a compact appearance that has led to them being named “little red dots”. In this paper, we develop a detailed framework to estimate the photometry of AGNs embedded in galaxies extracted from the OBELISK cosmological simulation to understand the properties of color-selected little red dots (cLRDs) in the context of the full AGN and massive black hole population. We find that using realistic spectral energy distributions (SEDs) and attenuation for AGNs we can explain the shape of the cLRD SED as long as galaxies host a sufficiently luminous AGN that is neither overly attenuated nor too little attenuated. When attenuation is too low or too high, AGNs do not enter the cLRD selection, because the AGN dominates over the host galaxy too much in blue filters, or it does not contribute to photometry anywhere, respectively. cLRDs are also characterized by high Eddington ratios, possibility super-Eddington ones, and/or high ratios between the black hole and the stellar mass.

@article{2025A&A...695A..33V, author = {{Volonteri}, M. and {Trebitsch}, M. and {Greene}, J. E. and {Dubois}, Y. and {Dong-Paez}, C.-A. and {Habouzit}, M. and {Lupi}, A. and {Ma}, Y. and {Beckmann}, R. S. and {Dayal}, P. and {Schneider}, R.}, title = {{Exploring active galactic nuclei and little red dots with the Obelisk simulation}}, journal = {\aap}, keywords = {black hole physics, galaxies: active, galaxies: high-redshift, Astrophysics - Astrophysics of Galaxies}, year = {2025}, month = mar, volume = {695}, eid = {A33}, pages = {A33}, doi = {10.1051/0004-6361/202451963}, archiveprefix = {arXiv}, eprint = {2408.12854}, primaryclass = {astro-ph.GA}, adsurl = {https://ui.adsabs.harvard.edu/abs/2025A\&A...695A..33V}, adsnote = {Provided by the SAO/NASA Astrophysics Data System}, dimensions = {true}, lrdkeys = {black hole mass, dust, photometry, sed, simulation}, month_numeric = {3} }

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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.