Weekly issue

Week 37, 2026

Sep 7–13, 2026

Week 37, 2026 includes 15 curated papers, centered on LRD, spectroscopy, high-z.

2609.10803v1

The THRILS Factor: Investigating the properties of Little Red Dots (LRDs) at 3<z<6 with JWST/NIRSpec

Ananya Ganapathy, Rebecca L. Larson, Erini Lambrides, Guillermo Barro, Taylor A. Hutchison, Pablo Arrabal Haro, Anthony J. Taylor, Dale Kocevski, Casey Papovich, Steven L. Finkelstein, Anton M. Koekemoer, Jonathan R. Trump, Pablo G. Pérez-González, Weida Hu, Volker Bromm, Dan Coe, Kelcey Davis, Michaela Hirschmann, Nikko J. Cleri, Ray A. Lucas, Stephan R. McCandliss, L. Y. Aaron Yung, Jorge A. Zavala

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Ganapathy et al. present deep JWST/NIRSpec spectroscopy of nine compact, V-shaped little red dots at 3<z<6 in the EGS, selected through the THRILS and C3PO programs. Broad Balmer and He I emission establish widespread AGN-like activity, while [S II] ratios imply electron densities comparable to local AGN narrow-line regions and other high-redshift galaxies. Five objects favor convolved exponential rather than Gaussian broad-line profiles, yielding inferred scattering columns of log(Ne/cm−2)=23.93–24.14 and sub-unity covering fractions that point to a clumpy BLR rather than the nearly closed obscuring geometry often assumed for LRDs. The resulting Compton-thick columns offer a route to their X-ray weakness, and the profile modeling also lowers black-hole mass estimates relative to Gaussian-only fits; the THRILS sample is notably narrow-line dominated compared with previously reported AGN-dominated LRDs.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. This figure establishes the photometric basis of the nine-object sample, showing how the compact, V-shaped THRILS LRDs occupy the adopted color-selection space relative to the full parent catalog and CEERS LRDs.
Figure 5. The multi-object Balmer-line fitting summary is the clearest direct evidence for the paper’s central profile result: five LRDs require convolved exponential broad components, while the remaining sources are adequately described by Gaussian profiles.
Figure 7. This diagnostic translates the measured [S II] doublet ratios into electron densities and shows that the THRILS LRDs resemble non-LRD comparison objects in density, supporting an NLR-like interpretation rather than an exceptional low-density gas phase.
Figure 8. This figure shows the practical consequence of profile choice for black-hole inference: convolved-profile measurements revise the Gaussian-based virial mass estimates, placing the THRILS LRDs in context with local and high-redshift black-hole–stellar-mass relations.
Figure 9. The full population comparison connects the sample to the paper’s evolutionary interpretation, contrasting the predominantly narrow-line-dominated THRILS LRDs with literature LRDs and broad-line AGN while relating UV luminosity to [O III] output.

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2609.09265v1

A Spectral Framework for Testing the Quasi-Star Hypothesis in Little Red Dots I: Weighing LRDs by Their Super-Eddington Luminosity Ratios---No Signs of Overmassive Black Holes

Olivia Curtis, Nikko J. Cleri, Jakob M. Helton, Joel Leja, Jason T. Wright

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Curtis et al. test whether little red dots can be quasi-stars, fitting Prospector host-galaxy models plus TLUSTY photospheres to four absorption-line LRDs and connecting the inferred temperatures, gravities, and luminosities to MESA-QUEST envelope calculations. All four primary sources are super-Eddington, with c6 = 4.0299, and yield 70027,000 M envelopes whose quasi-star mass caps place GN-28074 about five decades below its published virial black-hole mass estimate. Extending the analysis to 82 archival LRDs, the authors find population-wide super-Eddington photospheres and continuum-driven winds at roughly 13 times escape speed, interpreting the sequence as evolution from massive, slowly shedding envelopes to thinner, more eruptive ones. The most extreme c6 measurement lies at the boundary of the atmosphere grid and beyond the simulated regime, but the broader result argues that quasi-stars can reconcile LRD spectra and BHhost mass ratios without invoking overmassive black holes.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 4. This is the papers core self-consistency test: fitted photospheric components are placed against the Eddington limit and iso-c6 curves, then compared directly with converged MESA-QUEST tracks. It shows how the observed LRD states map onto super-Eddington quasi-star envelope solutions and how wind evolution connects the fitted hot and cold components.
Figure 5. This figure delivers the headline BHhost result. The quasi-star black-hole mass caps for the primary and archival LRDs lie on or below the local ReinesVolonteri relation, while GN-28074s published virial estimate is displayed as the discrepant comparison point.
Figure 6. The full-sample temperaturegravity diagram establishes that the super-Eddington inference is not restricted to the four detailed fits. It makes the population-level selection and posterior constraints visible, including the explicitly excluded unconstrained fits and the placement of the water-absorbing cold components.
Figure 7. This synthesis figure links envelope mass to outflow kinematics, supporting the proposed evolutionary interpretation. Its comparison to the continuum-driven wind limit shows that the measured LRD winds are consistent with radiation-dominated outflows, with low-c6 sources retaining the most massive, slowest envelopes.

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2609.09078v1

Small-Scale Clustering of Primordial Black Holes: The Little Red Dot Mass Function and the High-Redshift Galaxy Tension

Borui Zhang, Wei-Xiang Feng, Haipeng An

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Zhang, Feng, and An develop a primordial-black-hole cluster scenario in which long–short mode coupling produces dense PBH clusters whose runaway mergers seed the supermassive black holes associated with little red dots. Including subsequent accretion, the model derives an SMBH mass function consistent with LRD observations and connects black-hole mass to host-halo, stellar-mass, and gas-disk properties, naturally producing overmassive and compact systems when LRDs occupy low-angular-momentum halo components. The same high-mass PBH-cluster tail supplies early seeds that can boost galaxy formation and reduce the reported high-redshift stellar-mass-density tension with ΛCDM.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. This is the central population-level prediction: the SMBH mass function generated by PBH clusters through long–short mode coupling. It is the most direct figure for assessing the paper’s claim that, after accretion, the model can reproduce the LRD black-hole population.
Figure 2. This figure shows the stellar-to-BH ratios in PBH-cluster-induced haloes across star-formation-rate assumptions. It directly illustrates the mechanism invoked for the unusually overmassive black holes inferred in little red dots.
Figure 4. The effective-radius versus UV-luminosity relation provides the paper’s compactness diagnostic for seed-effect-induced galaxies. It is especially useful for connecting the PBH-cluster framework to the observed small sizes of LRD hosts.
Figure 5. This cumulative stellar-mass-density comparison at z≈10 captures the paper’s broader cosmological payoff: early SMBH seeds from PBH clusters can accelerate halo and galaxy growth. The cutoff-redshift dependence also makes clear which modeling choice controls the proposed relief of the high-redshift galaxy tension.

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2609.06239v1

Connecting the little dots in polarized light

Piero Madau, Roberto Maiolino, Francesco D'Eugenio

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Madau, Maiolino, and D’Eugenio model the polarized continuum and Balmer-line signal of the local LRD analog SDSS J1025+1402 in an orientation-based picture where little red dots are dust-obscured, high-inclination little blue dots powered by super-Eddington accretion. Electron scattering in a geometrically thick inner flow produces intrinsically polarized continuum emission, while unpolarized outer thin-disk light increasingly dilutes that signal toward optical wavelengths; a circumnuclear dust screen adds dichroic polarization to both continuum and broad Hα. Their combined Stokes-vector model quantitatively reproduces the roughly 1.5% continuum polarization, the lower roughly 0.7% broad-Hα polarization, and the position-angle offset because the line lacks the intrinsic disk-polarized component. The result makes spectropolarimetry a direct test of accretion-flow geometry and orientation in the little-dot population, though accretion rate and inclination remain degenerate.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. This figure establishes the central orientation diagnostic: continuum polarization rises with inclination, while the unpolarized thin disk suppresses the signal most strongly at optical wavelengths. It directly motivates why an inclined, obscured little-dot system can show modest but nonzero continuum polarization.
Figure 3. The polarization spectra show the predicted inclination dependence and the UV-to-optical decline caused by thin-disk dilution. This is the clearest population-facing prediction for testing the thick-plus-thin super-Eddington flow picture with future LRD spectropolarimetry.
Figure 4. This is the core observational comparison for SDSS J1025+1402, fitting intensity, normalized Stokes parameters, polarization fraction, and position angle across the continuum and broad Hα. It demonstrates how dilution of disk polarization relative to dichroic line polarization produces the observed lower line polarization and position-angle rotation.
Figure 5. The Stokes Q–U construction provides the most compact physical synthesis of the fit: intrinsically disk-polarized continuum and dichroic dust polarization combine vectorially, whereas broad Hα retains only the dichroic component. It makes the origin of the continuum-to-line polarization offset especially transparent.

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2609.11094v1

SPURS: An Ultra-deep View Inside the Compact, Nitrogen-Enriched Nuclei of Little Red Dots

Mengtao Tang, Daniel P. Stark, Charlotte A. Mason, Zuyi Chen, Tucker Jones, Sarah Searle Grannis, Peter Senchyna, Lily Whitler, Keerthi Vasan G. C., Viola Gelli

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SPURS presents ultra-deep JWST/NIRSpec rest-UV spectra of four UV-bright little red dots, resolving both their compact nuclear emission and the gas surrounding it. Two objects show broad C IV, one shows broad He II, and the sample combines unusually high narrow-line densities, pervasive nitrogen enhancement, and in some cases fast P-Cygni absorption consistent with powerful stellar or nuclear outflows. Strong low-ionization absorption, Lyα damping wings, and fluorescent Fe II and O I place a large neutral-gas column close to the UV source, while the higher incidence of nitrogen and strong C III] among LRDs points to an exceptionally dense nuclear environment, plausibly an assembling nuclear star cluster where dynamical stellar interactions help shape the abundance pattern.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 5. The C IV decompositions provide the paper’s clearest direct broad-line evidence, separating broad and narrow emission from multiple absorption components in GN-2 and CEERS-7902. This figure is central to the claim that at least some LRD UV continua offer a transmitted view toward a broad-line region or compact cocoon.
Figure 8. This density-diagnostic comparison shows that the four SPURS LRDs occupy electron-density regimes elevated above typical star-forming galaxies, with the extreme measurements framed against other LRDs and nitrogen-line emitters. It anchors the interpretation of an unusually compact, high-pressure nuclear environment.
Figure 13. The Lyα-profile fits directly demonstrate the damped absorption that implies the UV-emitting regions are embedded behind substantial neutral-gas columns. Together with the metal-line evidence, this is key to locating dense neutral material close to the nucleus rather than treating it as unrelated foreground absorption.
Figure 16. The C III] equivalent-width comparisons place the SPURS targets and the broader LRD literature against star-forming galaxies using rest-optical ionization diagnostics. It captures the population-level result that strong C III] is disproportionately common among LRDs, not merely a peculiarity of one source.
Figure 19. The concluding schematic synthesizes the proposed connection between LRDs, nitrogen-emitting galaxies, and unresolved dense stellar systems. It is the best figure for conveying the paper’s physical picture: compact nuclear star formation and stellar dynamics may contribute alongside accretion to the distinctive UV spectra and nitrogen enrichment.

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2609.11879v1

Learning JWST. I. A Foundation Model for New Population Discoveries and Morphology-Aware Photometric Redshift Measurements in the JADES Survey

Jiani Ding, Minghao Yue, Yongda Zhu, Xiaohui Fan, Yufeng Luo

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FM-JADES-v1 is a self-supervised, cross-modal foundation model trained on 482,444 JADES DR5 sources, jointly encoding 16-band NIRCam image cutouts and catalog measurements into a shared morphology-plus-photometry embedding. Without labels or population-specific cuts, its embedding space isolates high-redshift galaxies and an LRD-rich population as distinct islands, providing a data-driven route to retrieve rare candidates rather than beginning from conventional selections. In a controlled three-band F115W/F200W/F356W photo-z test, the learned representation reaches σNMAD = 0.157 versus 0.44 for template fitting, showing that image morphology can materially recover redshift information when photometric coverage is sparse. For LRD work, the paper is chiefly a methods result: it positions foundation-model embeddings as a scalable discovery layer for finding and characterizing unusual early-universe populations in future wide surveys.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1. This schematic establishes the paper's central technical claim: FM-JADES-v1 fuses separately tokenized multi-band imaging and catalog data in a shared Transformer embedding, then deploys that representation for both blind rare-population discovery and morphology-aware photometric redshifts. It is the most direct visual guide to how the LRD/high-redshift island search and the three-band photo-z improvement arise from the same trained model.

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2609.10319v1

Extending the Little Red Dot population at intermediate redshift with VIPERS

Krzysztof Lisiecki, Krzysztof Hryniewicz, Francesco Pistis, Michał J. Michałowski, Aidan P. Cotter, Maciej Koprowski, Miguel Figueira, Agnieszka Pollo, Katarzyna Małek, Olga Cucciati

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Lisiecki et al. search the 0.5<z<1.75 VIPERS survey for little-red-dot analogues, selecting V-shaped UV-to-optical continua from broadband slopes and retaining sources with broad spectral lines. They identify 14 compact V-LRDs, including one unresolved X-ray detection, and find that their comoving abundance drops rapidly after cosmic noon when placed alongside literature samples. The two objects with usable density-field measurements lie in underdense regions, while CIGALE modeling of the X-ray source favors a low-inclination, radiatively efficient accretion disk, extending empirical LRD constraints into the intermediate-redshift gap between local and JWST-era populations.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. This figure establishes the sample visually and spectroscopically: it shows the V-shaped rest-frame SEDs, the UV and optical slope measurements used for selection, the broad-line identifications, and compact imaging cutouts across the redshift range.
Figure 4. This is the paper's central evolutionary result, placing the two VIPERS number-density measurements against literature samples and showing the inferred rapid decline in LRD abundance after cosmic noon.
Figure 5. This figure presents the direct environmental test, comparing the two measurable V-LRD local densities with the VIPERS field and matched control distributions to show that both occupy underdense regions.
Figure 6. This figure gives the physical interpretation of the unique X-ray-detected V-LRD by comparing full UV-to-X-ray CIGALE fits and their residuals, highlighting why the preferred solution contains a radiatively efficient AGN disk viewed at low inclination.

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2609.09271v1

The Ashes of Supermassive Stars: Globular Cluster-like Aluminum Enhancement in Little Red Dots

V. Kokorev, J. Chisholm, R. P. Naidu, M. Gieles, S. Finkelstein, D. Berg, H. Akins, A. Taylor, S. Fujimoto, L. J. Furtak, J. Greene, A. de Graaff, K. Hawkins, T. Hsiao, D. Nandal, J. Matthee, S. Monty, P. Rinaldi, M. Boylan-Kolchin

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Using deep SPURS JWST/NIRSpec rest-UV spectroscopy of four bright little red dots, Kokorev et al. derive Mg, Al, Si, and Fe abundances from resolved absorption features in dense gas surrounding the central engines. The LRDs are metal poor, at roughly 1% solar metallicity, yet show an extreme globular-cluster-like signature of magnesium depletion and aluminum enhancement while retaining near-solar Si/Fe, unlike matched star-forming galaxies and conventional massive-star enrichment. The inferred 73–81 MK hot-hydrogen-burning conditions are consistent with fully convective supermassive stars of at least 10,000 solar masses, suggesting LRDs may expose these stars shortly before or after direct collapse. This provides a potential common origin for globular-cluster light-element anomalies and massive black-hole seeds.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. Shows the four compact SPURS targets and the inverse-variance-weighted rest-UV stack from which Mg, Al, Si, and Fe absorption measurements are extracted. It establishes both the sample definition and the observational basis for the abundance analysis.
Figure 2. This is the paper's central empirical result: the LRDs occupy the extreme Al-rich, Mg-poor extension of the globular-cluster abundance sequence while remaining strongly offset from matched high-redshift and local star-forming galaxies. The Si-versus-Al comparison further shows that the anomaly is not a generic metal-enrichment effect.
Figure 3. Contrasts alpha-capture enrichment with the hot-hydrogen-burning pathway that converts Mg into Al in fully convective stars. It provides the physical interpretation for why the observed combination of Mg depletion, Al enhancement, and limited Si production is diagnostic.
Figure 4. Connects the measured Mg, Al, and Si ratios to nucleosynthesis tracks and then maps the inferred core-temperature range onto stellar mass. This synthesis figure carries the conclusion that the polluting source must be a supermassive star with a mass of at least 10,000 solar masses.

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2609.09266v1

SHELLQs. Black Hole Mass and Eddington Ratio Distributions of Intermediate-Luminosity Quasars at 6<z<7

Masafusa Onoue, John D. Silverman, Yoshiki Matsuoka, Xuheng Ding, Camryn L. Phillips, Michael A. Strauss, Junya Arita, Takuma Izumi, Mahoshi Sawamura, Nobunari Kashikawa, Irham Andika, Kentaro Aoki, Shunsuke Baba, Anna-Christina Eilers, Seiji Fujimoto, Tomotsugu Goto, Masatoshi Imanishi, Kohei Inayoshi, Kazushi Iwasawa, Knud Jahnke, Yuki Kaneko, Toshihiro Kawaguchi, Kotaro Kohno, Chien-Hsiu Lee, Alessandro Lupi, Tohru Nagao, Dragan Salak, Malte Schramm, Yoshiki Toba, Hideki Umehata, Marta Volonteri, Fabian Walter, Feige Wang, Jinyi Yang

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Onoue et al. use JWST/NIRSpec broad Balmer-line spectroscopy and Subaru/MOIRCS Mg II measurements to estimate virial black-hole masses and Eddington ratios for 21 intermediate-luminosity SHELLQs quasars at 6.07 < z < 6.90, then combine them with earlier measurements into a 27-object z~6–7 sample. The quasars span 7.2 < log(M_BH/M_sun) < 9.4 and -1.3 < log(L_bol/L_Edd) < 0.4; relative to luminosity-matched z~1.3 SDSS quasars, the high-z population has median black-hole masses lower by 0.4 dex and Eddington ratios higher by 0.2 dex. About 11% are near- or super-Eddington accretors, rising to 22% under an Eddington-ratio-dependent single-epoch mass calibration, supporting rapid but less extreme early SMBH growth than in the most luminous z>6 quasars and bridging those objects to faint JWST AGN.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. Use this sample-definition figure to place the new targets in redshift–M_1450 space: SHELLQs fills the intermediate-luminosity interval between luminous EIGER/ASPIRE quasars and the faint JWST-selected AGN regime motivating the study.
Figure 7. This is the central empirical check on the Balmer-based mass machinery, comparing host-subtracted 5100 Å luminosities with broad Balmer-line luminosities and identifying two outliers, J0844-0132 and J1146-0005, relevant to the reliability of the adopted line diagnostics.
Figure 14. This synthesis figure directly shows where the z~6–7 SHELLQs quasars lie in black-hole-mass–luminosity and mass–Eddington-ratio space relative to luminous high-z quasars, faint JWST AGN, and consistently recalibrated SDSS quasars.
Figure 15. Use this conclusion-driving comparison to see the luminosity-matched distribution shift: the 27 SHELLQs quasars are systematically lower in black-hole mass and higher in Eddington ratio than the Monte Carlo-resampled z~1.3 SDSS population.
Figure 16. This systematic-test figure shows how an Eddington-ratio-dependent single-epoch mass calibration changes the inferred mass and accretion-rate distributions, underpinning the paper's higher 22% super-Eddington fraction estimate.

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2609.08145v1

The Roman eXtreme Deep Field (RXDF)

Haojing Yan, Anton M. Koekemoer, Yue Shen, Bangzheng Sun, Norman A. Grogin, Zihao Wu, Christian Kragh Jespersen, Rachel Somerville, Kyoung-Soo Lee, Dale D. Kocevski, Adam J. Burgasser, Pedro H. Bernardinelli, Yicheng Guo, Charles Steinhardt, Xiaohui Fan, Duncan Farrah, Gisella De Rosa, Feige Wang, Jinyi Yang, Lifan Wang, Fengwu Sun, Christopher N. A. Willmer, John David Silverman, Steven L. Finkelstein, Seth H. Cohen, Rolf A. Jansen, Rogier A. Windhorst, Brent M. Smith, Stefano Casertano, Anthony H. Gonzalez, Michael A. Strauss, Ray A. Lucas, Katherine E. Whitaker, Mingyang Zhuang, Rodrigo Angulo, Chloe Aurin, Micaela Bagley, Franz E. Bauer, Jessica M. Berkheimer, Rachel Bezanson, Alejandro S. Borlaff, Rebecca A. A. Bowler, Larry D. Bradley, W. N. Brandt, Denis Burgarella, Timothy Carleton, Delondrae D. Carter, Caitlin M. Casey, Christopher J. Conselice, Kyle W. Cook, Jeff Cooke, David A. Coulter, Tyler Desjardins, Tim Dewachter, Nicole E. Drakos, Simon P. Driver, Qiao Duan, Eiichi Egami, Andreas Faisst, Travis C. Fischer, Adriano Fontana, Ori Fox, Brenda Frye, Yoshinobu Fudamoto, Eric Gawiser, Mauro Giavalisco, Yuichi Harikane, Thomas Harvey, Nimish P. Hathi, Benne W. Holwerda, Taylor Hutchison, Olivier Ilbert, Akio K. Inoue, Lucy R. Ivey, Kartheik Iyer, Mathilde Jauzac, Ignas Juodzbalis, Jeyhan S. Kartaltepe, Daichi Kashino, Susan Kassin, Patrick Kelly, Kotaro Kohno, Stephanie LaMassa, Erini Lambrides, Rebecca Larson, Junyao Li, Zhiyuan Ma, Sangeeta Malhotra, Elizabeth McGrath, Peter Melchior, Marcio Melendez, Hironao Miyatake, Bahram Mobasher, Mireia Montes, Thomas Moore, Takahiro Morishita, Takashi Moriya, Leonidas Moustakas, Rohan Naidu, Rosalia O'Brien, Pascal A. Oesch, Masafusa Onoue, Rafael Ortiz, Masami Ouchi, Robert G. Pascalau, Molly Peeples, Andreea O. Petric, Sara Petty, Justin Pierel, Marc Rafelski, Eniko Regos, Armin Rest, Mitchell Revalski, James Rhoads, Pierluigi Rinaldi, Aaron Robotham, Kate Rowlands, Pablo M. Sanchez-Alarcon, Paola Santini, Alice E. Shapley, Raymond C. Simons, Swara Ravindranath, Takahiro Sumi, Takumi S. Tanaka, Masayuki Tanaka, Scott Tompkins, Christina C. Williams, Edward J. Wollack, John F. Wu, L. Y. Aaron Yung

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This program paper defines the Roman eXtreme Deep Field (RXDF), a Cycle 1–2 Roman imaging survey designed to reach AB = 30 mag over 678.75 arcmin² at full depth, with contiguous coverage totaling 1,243 arcmin² across seven Roman bands. Its central advance for the LRD and early-SMBH community is deep, wide-area imaging in the Euclid Ultra Deep Field near the North Ecliptic Pole, overlapping the JWST NEXUS Treasury field and substantially enlarging the volume available for rare AGN, LRD, and luminous-galaxy searches. Three annual epochs, each split into sub-epochs roughly 10 days apart, add variability baselines from about 10 days to more than two years, enabling time-domain discrimination and transient science alongside population measurements. The survey is positioned to reduce cosmic-variance limitations that currently dominate extreme-depth HST and JWST fields while extending LRD searches to substantially lower luminosities at cosmic noon.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 3. This is the operational survey-definition figure: it shows how the customized eight-point dithering and shifted centers fill detector gaps across nine sub-epochs, producing the 678.75 arcmin² full-depth region and 1,243 arcmin² contiguous footprint that underpin the program’s rare-object statistics.
Figure 4. This figure places RXDF within the Euclid Ultra Deep Field and JWST NEXUS footprint, then compares its depth and area directly with the Hubble eXtreme Deep Field, existing JWST surveys, and Roman HLTDS. It is the clearest visual summary of why RXDF occupies a distinct depth–area regime.
Figure 5. This cosmic-variance calculation makes the survey’s core statistical case, showing how RXDF’s area changes the probability of finding the brightest high-redshift galaxies relative to JADES and HUDF-sized fields. The same volume advantage is directly relevant to constraining rare LRD and AGN populations.
Figure 7. The right-hand luminosity–redshift comparison is the most directly relevant science forecast for this archive: RXDF is projected to yield a high-redshift AGN sample comparable in depth to the deepest JWST samples but 30–50 times larger, while reaching cosmic-noon LRD luminosities roughly ten times below those accessible for high-redshift JWST LRDs.

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2609.06926v1

Little Red Dot Cosmology: A Matter-Era Baryon Acoustic Oscillations Probe of $Λ$CDM

Jessica A. Zebrowski, Rohan P. Naidu

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Zebrowski and Naidu propose little red dots as a new large-scale-structure tracer for baryon acoustic oscillation measurements across the otherwise sparsely mapped matter-dominated interval at 4≲z≲9. Using a Fisher forecast calibrated with empirical LRD-like number densities of roughly 10^-4 h^3 Mpc^-3, a bias rising from about 3 to 8, and a DESI-scale 14,000 deg² spectroscopic footprint, they forecast percent-level constraints on the isotropic distance scale D_V/r_d in four redshift bins. The case rests on LRDs combining high bias and abundance with unusually efficient identification through compact rest-optical morphology, a V-shaped SED, and luminous broad Hα emission, making them a concrete target for future near- and mid-infrared redshift surveys testing ΛCDM deep in the matter era.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. Use this overview to establish the core cosmological motivation: LRDs fill the redshift gap between low-redshift galaxy BAO surveys and the CMB, in an era where dark energy is dynamically negligible and ΛCDM makes a particularly clean distance-scale prediction.
Figure 3. This is the forecast-input figure. It connects the argument to measurable LRD properties by showing the assumed redshift evolution of bias, number density, and available comoving volume for a 14,000 deg² survey, including comparisons to established DESI tracer samples.
Figure 4. This is the conclusion-driving result: forecast LRD measurements extend percent-level D_V/r_d constraints from the DESI low-redshift BAO regime to 4≲z≲9, directly visualizing the proposed matter-era standard-ruler test.

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2609.07025v1

Between Little Red Dots and Star-Forming Galaxies: A Sequence in the Optical Continuum Slope

Kristiphong Boonmee, Akio K. Inoue, Masafusa Onoue, Xingyao Cai

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Using 3,566 DAWN JWST Archive NIRSpec/PRISM spectra at 3≲z≲8, Boonmee et al. fit rest-frame UV and optical power-law slopes and map galaxies in the βUV–βopt plane without preselecting LRDs. They find a smoothly populated, near-vertical sequence from ordinary star-forming galaxies into the LRD region, including an overlooked ≈50-object transition population at −1≲βopt≲0 whose stacked NIRCam morphologies are intermediate between extended galaxies and point-like LRDs. Linear mixtures of star-forming stacks and The Cliff BH* template reproduce the sequence and imply MBH/M*≈0.006–0.1 at its LRD end, supporting a picture in which LRDs are the compact, BH*-dominated extreme of a continuous host-plus-central-source population rather than a sharply separate class.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 3. This is the central observational map: it shows the full βUV–βopt distribution, conventional V-shaped and LRD selection boundaries, and the vertical population that extends continuously from non-LRD star-forming galaxies into the red LRD region.
Figure 7. The BH* plus host mixing tracks provide the paper’s key physical interpretation, demonstrating how varying the relative BH* contribution can move stacked star-forming spectra along the observed vertical sequence toward The Cliff and the LRD population.
Figure 8. This figure operationalizes the proposed transition selection by dividing the vertical sequence into four βopt bins after isolating the trend, making the intermediate population and its progression toward the LRD end explicit.
Figure 10. The rest-frame UV stacked morphologies and extendedness ratios test whether structural properties evolve coherently along the continuum-slope sequence, linking the spectral transition to changing compactness.
Figure 11. The corresponding rest-frame optical stacks are especially important for the BH*-dominated interpretation, because the optical component is where the sequence becomes redder and increasingly compact relative to star-forming hosts.

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2609.09274v1

Overmassive No More: The Case for Little Red Dots Hosting Black Hole Seeds as Massive as Single Supermassive Stars

Wendy Q. Sun, Rohan P. Naidu, Hanpu Liu, Anna de Graaff, Jenny E. Greene, Jorryt Matthee, Chris Ashall, John Chisholm, Anna-Christina Eilers, Qinyue Fei, Kasper E. Heintz, Daichi Hiramatsu, Vasily Kokorev, Joel Leja, Zhaoran Liu, Priyamvada Natarajan, Pascal A. Oesch, Robert A. Simcoe, Alberto Torralba, Andrea Weibel

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Sun et al. recast the host-subtracted continua of 117 Little Red Dots as cool, optically thick pseudo-photospheres surrounding their central engines, fitting tailored stellar-atmosphere models to stacked spectra. The inferred BH* temperatures are tightly clustered at about 4200–4800 K, with luminosities of roughly 10^43–10^45 erg s^-1 and photospheric radii of about 700–2000 au. Four non-virial mass estimates, based on fitted surface gravity, super-Eddington analogies, outflow escape speeds, and the observed lack of variability, converge on central masses of about 10^4–10^5 solar masses and Eddington ratios of about 5–50. This removes the need for 2–3 dex overmassive black holes, places the sources near the local black-hole–host relation, and links both their masses and luminosity-function cutoff to the maximum mass of single supermassive stars, making LRDs plausible newly born heavy seeds.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 2. This is the essential selection-and-decomposition figure: matching hosts by redshift and [O III] luminosity isolates the BH* component and reveals the red optical continuum and Balmer break that motivate the pseudo-photosphere interpretation.
Figure 5. The HR-diagram comparison places BH*s in the unusually cold, luminous regime occupied by dense-wind pseudo-photospheres, visually connecting their narrow 4200–4800 K temperature range to hydrogen-recombination regulation.
Figure 6. This figure makes the paper's central revision immediately clear by comparing the median non-virial BH* mass with local virial-calibration estimates at fixed host stellar mass, showing why the apparent overmassive-black-hole problem disappears.
Figure 7. This three-substack synthesis is the conclusion-driving figure: all four mass-estimation approaches yield masses below the general-relativistic upper limit for single supermassive stars, directly supporting the heavy-seed birth scenario.

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2609.07825v1

A Dusty Quenching-candidate AGN host at z=5.7: massive quiescent galaxies may quench already during the dust-obscured phase

Francesco D'Eugenio, Matilde Brazzini, Roberto Maiolino, Elena Bertola, Stefano Carniani, Xihan Ji, Ignas Juodžbalis, Yixiao Liu, Minjung Park, Eleonora Parlanti, Robert G. Pascalau, Gabriele Pezzulli, Jan Scholtz, Sandro Tacchella, Stefano Zibetti

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D’Eugenio et al. present a spectro-photometric analysis of RUBIES-EGS-9809, a compact broad-line AGN host at z=5.7 that is deeply reddened (A_V > 3 mag), dust-rich, and Compton-thick in X-rays. Its spatially resolved 0.6-kpc Balmer break and inferred stellar mass of log(M*/M_sun)=10.7±0.3 indicate an evolved stellar population embedded in an obscured system, while strong Na I absorption and broad [O III] point to multiphase outflows plausibly powered by the AGN. Although the declining recent SFH cannot be securely established from the low-resolution spectra, the authors identify a strong quenching candidate and propose that quenching can occur before dust clears, hiding the expected UV-bright 50–100 Myr transition population between dusty starbursts and dust-free quiescent galaxies.

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Key figures to inspect

Figure 1. Use this as the observational overview: the NIRCam morphology and paired RUBIES/CAPERS spectra establish the compact target, weak dust-suppressed UV continuum, Balmer break, broad emission, and conspicuous absorption that motivate the quenching-candidate interpretation.
Figure 2. This multi-band image-model decomposition shows the wavelength-dependent morphology, with more extended rest-frame UV emission and a nearly unresolved rest-frame optical component, providing key spatial context for separating stellar light from the dominant AGN point source.
Figure 5. The joint prism and G395M spectral fits provide the paper’s direct line-profile evidence for an outflow component, linking the broad rest-optical emission to the proposed AGN-driven, multiphase feedback episode.
Figure 8. This SFH comparison places RUBIES-EGS-9809 alongside massive quiescent galaxies and the dusty quenching system Hyde, showing why its assembled stellar population is consistent with a progenitor already approaching quiescence rather than an ordinary active starburst.
Figure 10. The concluding cartoon distills the proposed dusty path to quiescence: star formation declines while the galaxy remains obscured, AGN feedback can remove gas and dust, and the system emerges only later as an already evolved dust-poor quiescent galaxy.

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2609.11104v1

Nitrogen-Loud Quasars from the Dark Energy Spectroscopic Instrument. I. Sample Selection and Basic Properties

Shuo Zhai, Wei-Jian Guo, Yong-Jie Chen, Zhi-Qiang Chen, Haining Li, Jian-Min Wang, Gang Zhao

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Zhai et al. construct the largest homogeneous catalog of nitrogen-loud quasars to date, selecting 1,993 DESI DR1 objects at 1.6 < z < 4.3 with strong broad N IV] λ1486 and/or N III] λ1750 emission from a 168,500-object parent sample. These quasars comprise about 1.2% of the parent population, cluster more strongly around z ~ 2.5–3, and retain a similar UV continuum while showing markedly enhanced N V, N IV], and N III] plus more moderate strengthening of other metal lines. Against redshift- and luminosity-matched controls, they have narrower C IV and Mg II, lower single-epoch virial black-hole masses, and higher Eddington ratios, consistent with preferential identification during rapid accretion; the catalog establishes a large baseline for separating overall metallicity from selective nitrogen enhancement in future line-ratio modeling.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1. This flowchart defines the statistically clean DESI selection, from the 168,500-object parent sample through local N III] signal-to-noise screening, equivalent-width cuts, and visual inspection to the final 1,993-object catalog. It is essential for interpreting the reported 1.2% incidence and the meaning of the N-loud classification.
Figure 6. The composite-spectrum comparison is the paper’s clearest population-level spectral evidence: N-loud quasars have a broadly comparable UV continuum to parent DESI quasars but substantially stronger nitrogen features. It directly supports the claim that the sample is chemically and/or BLR-physically distinctive rather than simply continuum-selected.
Figure 8. This comparison of C IV and Mg II equivalent widths and FWHM against the matched SDSS control visualizes the systematically narrower broad lines in the N-loud population. Those line-width offsets underpin the subsequent differences in virial mass and inferred accretion state.
Figure 9. The black-hole-mass versus Eddington-ratio plane provides the conclusion-driving physical interpretation: DESI N-loud quasars occupy lower single-epoch virial masses and higher Eddington ratios than matched controls. It is the strongest figure for the proposed connection between nitrogen-loudness and a rapid black-hole-growth phase.
Figure 10. The N-loud fraction under several continuum signal-to-noise thresholds tests whether the apparent redshift dependence is driven by spectral-quality selection. It provides an important observational-selection check on the catalog’s demographic interpretation.