Weekly issue

Week 4, 2026

Jan 19–25, 2026

Week 4, 2026 includes 10 curated papers, centered on QSO, high-z, LRD.

2601.16772v1

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

M. Lopez-Corredoira, C. M. Gutierrez

Theme match 5/5

Digest

The authors re-analyze 31 z≈6–10 “little red dots” with V‑shaped SEDs using HST+JWST photometry, NIRSpec spectra for 13, and mid‑IR data for 15, fitting mixed stellar populations, nebular lines, possible AGN, and both ISM and IGM extinction with updated curves. Accounting for the low rest‑NIR fluxes, they infer that AGN contribute little at the reddest wavelengths on average and derive an average oldest‑stellar‑population age of 0.61±0.31 Gyr (95% CL), implying z_form > 11.2 (97.5% CL). The reddest SEDs yield the largest ages, and one extreme source appears older than the Universe at >4.7σ, a tension not explained by TP‑AGB effects. The authors note remaining model uncertainties, so the age–cosmology tension is provisional but sharpened by spectroscopy and the extinction treatment.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1 (extinction curves): Compare the Weingartner & Draine UV extension vs. a Calzetti extrapolation to see how the chosen dust law steepens rest‑UV attenuation and drives the need for an older stellar component while limiting AGN reddening leverage.
Fig. 2 (IGM attenuation): Inspect the Inoue et al. (2014) intergalactic extinction curves to gauge how Lyman‑series absorption sculpts the Lyα break and the V‑shaped SED, affecting redshift and age–dust degeneracies.
Fig. 3 (stacked NIRSpec rest‑frame 1000–5500 Å): Use the stack to assess Balmer/4000 Å break strength and search for Hβ and [O III] features; the zoom around 4770–5100 Å tests for broad vs. narrow Hβ and informs how typical the AGN component is across the sample.
Fig. 4 (GALAXEV index predictions): Map observed break/absorption strengths (e.g., D4000 and Hδ) to the age–metallicity grid to see why the fits favor ~0.5–0.8 Gyr ages and why the reddest SEDs push to even older solutions.

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2601.14368v1

The Little Red Dots Are Direct Collapse Black Holes

Fabio Pacucci, Andrea Ferrara, Dale D. Kocevski

Theme match 5/5

Digest

Radiation-hydrodynamic simulations post-processed with Cloudy show that compact Little Red Dots are best explained as accreting Direct Collapse Black Holes embedded in dense, compressionally heated, collisionally ionized flows. The Compton-thick inflow both suppresses soft X-rays and imprints the Balmer absorption via n=2 photoelectric opacity, while reprocessing disk radiation to produce the V-shaped SED with only modest dust attenuation consistent with high‑z curves. A single, purely DCBH-powered spectrum reproduces the prototypical RUBIES‑EGS‑42046 without invoking stars, matching the blue and red arms and line mix with small residuals. This framework unifies weak X-rays, metal/high‑ionization lines without strong star‑formation features, compact sizes, overmassive BHs, and number/redshift trends, implying long‑lived (>100 Myr), slowly variable seed-growth phases in pristine atomic‑cooling halos.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1 — Radial density, cumulative NH, velocity, and optical-depth profiles: verify the Compton-thick core and where τ drops outside a few pc; note the nearly hydrostatic inner region and low‑speed outer outflow that set the spectral filtering.
Fig. 3 — Data–model SED comparison for RUBIES‑EGS‑42046: inspect how n=2 photoelectric absorption converts the intrinsic Balmer jump into the observed break and how both V‑arms are matched; check residuals (e.g., near [O III]) and the shape/strength of the adopted dust law.
Fig. 4 — Broadband DCBH spectrum from FIR to hard X-rays: confirm reprocessed IR power and suppressed soft X-rays in the thick phase, and note the prediction that later, gas‑depleted stages become X‑ray bright—useful for multiwavelength tests.
Fig. 2 — Schematic of the DCBH inflow/outflow structure: use it to connect the dense, hot inner regions and dusty outer layers that act as the Balmer‑absorbing screen and to visualize radiation‑pressure‑regulated, mildly super‑Eddington accretion.

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2601.17416v1

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

Matthew Stepney, Manda Banerji, Shenli Tang, Matthew J. Temple, Paul C. Hewett

Theme match 4/5

Digest

Analysis of rest-UV–IR SEDs for 63 heavily reddened quasars at z=0.7–2.7 (E(B−V)=0.4–1.8) shows that >82% display “V-shaped” SEDs with a UV excess over a reddened quasar continuum. Two-component fits favor a reddened quasar plus an unobscured scattered-light contribution with a small average scattering fraction (~0.3%), though UV light from a star-forming host cannot be excluded. Four HRQs meet LRD UV/optical slope criteria, and the sample exhibits a near-IR hot-dust deficit relative to blue quasars—consistent with a phase where AGN feedback has ejected inner-torus dust. The UV scattering fraction weakly tracks hot-dust strength and anti-correlates with E(B−V), supporting hot dust as the scatterer and ISM-scale dust along the line of sight.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Check where HRQs sit in the z–L3000 plane versus blue SDSS quasars and how E(B−V) varies across the locus; confirms the luminosity range of the V-shaped objects and selection space.
Figure 2: Inspect the Eddington-ratio distributions to see HRQs skew toward (near-/super-)Eddington accretion compared to blue quasars, reinforcing a rapid-growth, feedback-prone phase.
Figure 3: Compare the “confirmed/inconclusive/rejected” SED fits to visualize the UV upturn, the decomposition into reddened-quasar vs scattered/host components, and the photometric leverage needed blueward of the inflection.
Figure 4: Examine the anti-correlation between scattering fraction and (i−K), showing how the legacy (i−K)=2.5 cut biases against high-scattering objects and why only a subset satisfy LRD-like slopes.

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2601.15962v1

Undermassive Hosts of $z = 4-6 $ AGN from JWST/NIRCam Image Decomposition with CONGRESS, FRESCO, and JADES

Zheng Ma, Eichi Egami, Yongda Zhu, Fengwu Sun, Jianwei Lyu, Junyu Zhang, Christopher N. A. Willmer, Andrew J. Bunker, Stefano Carniani, Emma Curtis-Lake, Ryan Hausen, Xihan Ji, Zhiyuan Ji, Ignas Juodžbalis, Roberto Maiolino, George H. Rieke, Pierluigi Rinaldi, Yang Sun, Sandro Tacchella, Hannah Übler, Christina C. Williams

Theme match 4/5

Digest

NIRCam image decomposition of 17 broad Hα–selected, low-luminosity AGN at z≈4–6 in JADES GOODS-N (CONGRESS+FRESCO) isolates host emission in 9/17 sources across 0.9–2.0 μm using GALFIT+MCMC. For those with detected hosts, stellar masses from decomposition-informed SEDs are 1–2 dex lower than photometry-only fits, yielding extreme BH-to-stellar mass ratios of M_BH/M_* ≈ 0.01–1.48—well above the local relation. Despite this, host size–mass measurements broadly align with established trends. The results point to genuinely under-massive hosts or hosts so compact they remain unresolved, underscoring strong early BH growth relative to their galaxies.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (NIRCam RGB cutouts): Scan GN1014406 and the GN1089xxx/GN1087xxx objects to see compact nuclei with faint, aligned extended structure; note the alternative RGB construction for GN1089568, GN1085355, GN1090549, GN1087388 and how rest-UV light appears despite red colors.
Figure 2 (GN1014406 decomposition): Use the AGN-subtracted SW-band panels and radial profiles to confirm resolved host flux and improved residuals versus a PSF-only fit (compare reduced χ² columns); this illustrates the methodology behind host detections across the sample.
Figure 3 (SED fits, 4 examples): Compare solid (with decomposition) vs dashed (total-photometry-only) models to see how adding AGN+host separation lowers M_* and reveals AGN components in cases where photometry alone missed them; inspect the partition of flux between AGN (green) and stars (orange).
Figure 4 (Stellar mass comparison): Track object-by-object shifts relative to Zhang et al. 2025 via the dashed connectors; the blue/orange coding shows which sources exhibit AGN signatures in photometry-only fits, quantifying the typical 1–2 dex M_* reductions.

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2601.15960v1

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

Zihao Wu, Daniel J. Eisenstein, Benjamin D. Johnson, Kevin Hainline, William M. Baker, Andrew J. Bunker, Alex J. Cameron, Emma Curtis-Lake, A. Lola Danhaive, Ryan Hausen, Jakob M. Helton, Zhiyuan Ji, Tobias J. Looser, Roberto Maiolino, Petra Mengistu, Pierluigi Rinaldi, Brant E. Robertson, Fengwu Sun, Sandro Tacchella, James A. A. Trussler, Christina C. Williams, Christopher N. A. Willmer, Joris Witstok

Theme match 4/5

Digest

Using deep JADES/NIRCam imaging in GOODS-S, the authors identify a z≈10.5 overdensity of 18 robust F115W-dropout galaxies within ~8 comoving Mpc. The region shows ~4× the field number density and accounts for about one-third of comparably bright galaxies and nearly half of the total SFR at 10<z_phot<12. Two compact members exhibit apparent Balmer breaks—consistent with evolved populations or little red dots—and ~1/3 of members have <1 kpc companions/substructure, while typical properties (M_* ~0.6–3×10^8 Msun, r_e ~200 pc, SFR ~5 Msun/yr) follow known high‑z scalings. Photometric variation in Lyα transmission hints at an emerging ionized bubble, though the system remains a photometric overdensity pending spectroscopy.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1 (sky map + density contours): Verify the west-side peak where the kernel-density estimate exceeds 4× the mean; check how excluding the three less-secure objects affects the significance within the F115W footprint and depth variations.
Fig. 2 (cutouts + layout): Inspect the F115W dropouts and rest-UV morphologies; note pairs/substructures within ≲1 kpc, the double components in objects D and K, and the foreground blue companion to F that is not at the overdensity redshift.
Fig. 3 (SEDs with Prospector fits): Examine the F444W-side flux break locations relative to NIRCam filter curves to assess true Balmer breaks versus emission-line contamination; consider the LRD interpretation for the two compact sources.
Fig. 4 (scaling relations): Compare overdensity members to field controls in UV slope–M_UV, size–mass (ForcePho), and SFR–mass to see that they track typical high‑z trends while highlighting the Balmer‑break candidates in red.
Supplementary/appendix maps (if provided): Look for the spatial pattern used to infer Lyα transmission variations and the putative ionized-bubble geometry across the overdensity footprint.

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2601.15384v1

An Analysis of AGN Feedback in the Compact Galaxy Group Stephan's Quintet

Maura Kathleen Shea, D. Michael Crenshaw, Travis C. Fischer, Mitchell Revalski, Julia Falcone, Beena Meena, Zo Chapman, Jacob Tutterow, Madeline Davis, Kesha Patel

Theme match 4/5

Digest

Spatially resolved long-slit spectroscopy across Stephan’s Quintet, with multi-Gaussian decomposition of Hα+[N II], is used to untangle ionized-gas kinematics across the group. The authors build the first biconical outflow model for NGC 7319’s NLR, finding radial velocities up to 550 km s−1 peaking at 2.6 kpc. Combining bicone, rotation, and group-scale maps, they locate a transition from AGN-powered outflows to gravitationally driven tidal flows at projected 2.4–6.3 kpc, with Seyfert-like ionization out to 6.3 kpc. This clean separation of components clarifies how AGN feedback and tidal dynamics co-exist in a dense compact group.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Slit layout over a JWST/NIRCam+MIRI image of Stephan’s Quintet: verify where the long slits cross NGC 7319, the NGC 7319–7318B bridge, and the shock ridge; read off the projected radii that bracket the 2.4–6.3 kpc transition zone.
Example Hα+[N II] line-profile fits along the slit: inspect how multiple Gaussian components isolate outflow, rotation, and tidal streams; note asymmetries and component separations near the nucleus vs. in the bridge.
Position–velocity diagrams with the adopted biconical outflow model overplotted: check the maximum radial velocity (~550 km s−1), the velocity peak at ~2.6 kpc, and constraints on opening angle and inclination.
Radial or 2D maps of line ratios (e.g., [N II]/Hα or BPT classifications): confirm Seyfert-like ionization persisting to ~6.3 kpc and where tidal/shock-dominated excitation takes over beyond that radius.
Kinematic maps or model–data residuals separating rotation from tidal flows: look for regions where non-circular motions dominate, especially along the NGC 7319–7318B tidal bridge.

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2601.14905v1

The eJWST active galactic nucleus observation catalogue

Virginia Lenk, Alvaro Labiano, Chiara Circosta, Almudena Alonso-Herrero, Dominika Wylezalek

Theme match 4/5

Digest

This paper releases the eJWST AGN observation catalogue, a curated list of JWST pointings containing AGN assembled from archive keywords, manual program review, and cross-matches to major AGN lists (Million Quasar, SDSS MaNGA AGN, CDFS). The catalogue spans 3,242 unique AGNs and records target identifiers, coordinates, redshifts, and per-observation details (instrument, aperture, filter), with direct download links in eJWST. Built via TAP+/ADQL queries to eJWST’s CAOM through astroquery, it includes both targeted and serendipitous AGNs present in the FoV, plus calibration/background data. The release enables immediate population studies and efficient follow-up across redshift and observing modes.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 2 (redshift histogram): inspect the z-coverage and where the sample is densest to gauge feasible bins for stacking or selection-limited analyses.
Fig. 3 (NGC 3079 coordinate comparison): see how SwiftBAT vs Milliquas coordinates shift the target relative to a specific MIRI FoV, illustrating cross-match provenance and positional uncertainties.
Fig. 4 (NGC 2936, MIRI F770W): shows that FoV polygons can include masked zones from coronagraphs—an AGN can lie inside the geometric FoV yet have no usable pixels.
Fig. 1 (target_keywords snippet): clarifies the APT category/description labels that seeded the initial AGN selection, useful for reproducing the keyword-based query.

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2601.16977v1

ReveaLLAGN 1: JWST Emission-Line Spectra Reveal Low-Luminosity AGN with UV-Deficient SEDs and Warm Molecular Gas

Kameron Goold, Anil Seth, Mallory Molina, David Ohlson, Nischal Acharya, Torsten Böker, Antoine Dumont, Michael Eracleous, Anja Feldmeier-Krause, Juan Antonio Fernández-Ontiveros, Elena Gallo, Andy D. Goulding, Kayhan Gültekin, Luis C. Ho, Nadine Neumayer, Richard M. Plotkin, Almudena Prieto, Jessie C. Runnoe, Shobita Satyapal, Glenn van de Ven, Jonelle L. Walsh, Feng Yuan, Nora Lützgendorf

Theme match 3/5

Digest

JWST/NIRSpec and MIRI IFU spectra for eight nearby LLAGN (plus Cen A) cleanly isolate the nuclei, enabling detections of high–ionization lines more than an order of magnitude fainter than before. Emission-line diagnostics show a transition near log(Lbol/LEdd) ≈ −3.5 where the SED becomes increasingly UV-deficient, while [Ne V] 14 μm and [O IV] 26 μm remain tightly correlated down to the lowest luminosities. The nuclear molecular gas is unusually warm, with rotational H2 temperatures ≈500 K higher than in luminous AGN and star-forming galaxies, and most targets show compact 10 μm silicate emission. High-S/N forbidden-line profiles also reveal IP-dependent kinematics, including double-peaked structure in M87 with a peak dominance change around 23 eV, underscoring feedback-shaped nuclear environments in LLAGN.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Scan the nuclear spectra (normalized to MIRI/MRS ch.1) to inventory high-IP lines per target and verify that NGC 4395’s line roster and continuum features are captured within the NIRSpec/MIRI coverage gaps.
Figure 2: Inspect the forbidden-line profiles across IP to see the kinematic stratification; in M87 note the systematic double peaks and the switch in dominant peak near IP ≈23 eV, and compare widths/offsets (≈+280/−450 km/s) across the sample.
Figure 3: Check nuclear/annular flux ratios against the point-source expectation to confirm the emission is unresolved and minimally host-contaminated, and look for any outliers versus Eddington ratio.
Figure 4: Use the [Ne V] 14 μm vs [O IV] 26 μm plane to verify the extension of the correlation to very low luminosities (with M94 as the faint end) and to benchmark ReveaLLAGN nuclei against legacy samples.

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2601.15186v1

Probing Heavily Obscured AGN in Major Galaxy Mergers Using the mm-X-ray Correlation

M. Droguett-Callejas, E. Treister, L. Barcos-Muñoz, M. Johnstone, F. E. Bauer, T. Kawamuro, N. Torres-Albà, C. Ricci, M. Koss, Y. Song, A. Peca, A. Evans, J. González

Theme match 3/5

Digest

Tests whether the millimeter (~200 GHz, 1.3 mm)–hard X-ray (14–150 keV) luminosity correlation can reveal buried SMBH activity in local (U)LIRG mergers using archival ALMA continuum for GOALS systems plus the confirmed dual-AGN UGC 4211. The sample yields three sources—one confirmed AGN and two strong candidates—with the confirmed dual AGN lying within ~3σ of the mm–X-ray relation, consistent with accretion-powered mm emission even at Compton-thick columns. Offsets from the correlation combined with independent star-formation rate constraints (and NH where available) provide a practical way to apportion AGN vs. star-formation contributions. While based on a small, heterogeneous local set and empirical scalings, the work argues that compact mm continuum is a dust-insensitive diagnostic for hidden SMBH growth; ALMA resolves nearby nuclei now and ngVLA will scale this to larger, more distant samples.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

mm (∼200 GHz) luminosity vs. hard X-ray (14–150 keV) luminosity with the best-fit relation and 1–3σ bands; highlight positions of confirmed dual AGN and the two candidate AGN to see who lands within ~3σ and who deviates.
ALMA 1.3 mm continuum maps of late-stage mergers (including UGC 4211), showing compact nuclear peaks and dual-nucleus separations; compare with X-ray centroid marks to assess astrometric alignment and plausibility of AGN-powered mm cores.
Diagnostic panel using each source’s offset from the mm–X-ray correlation combined with independent SFR limits to infer the AGN vs. star-formation share of the mm flux; look for cases where SF alone cannot explain the mm luminosity.
Column density NH versus offset from the mm–X-ray relation to evaluate how Compton-thick candidates behave relative to the correlation and whether extreme NH systematically shifts sources.
Summary table/plot of sample definition and ALMA setup (programs 2016.2.00055.S and 2017.1.00767.S): beam sizes and continuum fluxes per nucleus, to judge whether the mm emission is compact enough to be nuclear rather than extended SF.

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2601.16710v1

One H2 molecule per ten million H-atoms reveals sub-pc scale cold overdensities at z~4

P. Noterdaeme, S. Balashev, T. Berg, S. Cristiani, R. Cuellar, G. Cupani, S. Di Stefano, V. D'Odorico, C. Fian, B. Godard, S. López, D. Milaković, A. Trost, L. Welsh

Theme match 2/5

Digest

Ultra-high-resolution VLT/ESPRESSO (R~120,000) spectroscopy reveals exceptionally weak H2 Lyman–Werner absorption at z=4.24 toward J0007-5705, the highest-redshift H2 detection to date with N(H2)≈2×10^14 cm^-2 (~10^-7 fraction). Two components separated by ~3 km/s are resolved: a CNM-like narrow cloud (b≈1.7 km/s, nH≈10^2.8 cm^-3, T≈40 K) and a warmer, more turbulent phase (b≈6.2 km/s, nH≈10^1.4 cm^-3, T≈600 K) under a moderate UV field. Column densities and excitation imply path lengths down to ~0.01 pc, pointing to tiny cold overdensities in otherwise neutral gas. Finding one such case among just seven EQUALS DLAs argues these sub-pc cloudlets may be common yet usually invisible, showcasing the leverage of ultra-high spectral resolution.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the high-order H I Lyman series edges that pin down N(H I) and z; note how the reconstructed Lyα emission anchors the continuum across the DLA trough.
Figure 2: Check the Voigt-profile decomposition that isolates two H2 components only ~3 km/s apart and their alignment (or lack thereof) with metal components, while verifying which features are Lyα-forest or telluric blends.
Figure 3: Read the J=0–3 rotational population diagrams for each component—contrast the ~40 K narrow-phase excitation with the ~600 K broader phase and how Cloudy models outperform single-T fits.
Figure 4: Examine the UV-field vs density posteriors that separate the high-nH narrow cloud from the lower-nH broad phase; note the degeneracies and the moderate UV field consistent with several-Mpc distance from the quasar.