Weekly issue

Week 35, 2025

Aug 25–31, 2025

Week 35, 2025 includes 7 curated papers, centered on LRD, spectroscopy, high-z.

2508.21678v1

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

Lulu Bao, Chao-Wei Tsai, Jingwen Wu, Tao Wang, Guodong Li, Roberto J. Assef, Tanio Diaz-Santos, Peter R. M. Eisenhardt, Daniel Stern, Andrew W. Blain

Theme match 5/5

Digest

The authors stack NIRCam+MIRI photometry for 326 “V-shape” LRDs (from Akins24 and Kokorev24) and compare their UV–NIR SEDs to median-stacked Blue-excess Hot DOGs (BHDs) to test the analog hypothesis. Despite superficially similar “V-shapes,” LRDs turn over at shorter wavelengths, have much bluer rest-IR continua, show F1800W non-detections in stacks, and require far lower dust attenuation in SED fits—indicating little or no AGN-heated hot dust. They also argue the UV excess in LRDs is unlikely to be scattered AGN light, and note compact morphologies plus lower X-ray detection frequencies. Bottom line: LRDs are not simply high‑z siblings of BHDs, pointing to a distinct early SMBH growth pathway from the super‑Eddington, merger-driven Hot DOG phase.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect where the LRD “V” turns relative to the Hot DOG envelope; note the very low vs high attenuation AGN templates (A≈0.02 and ≈2.5 mag) needed, and the stacked F1800W upper-limit triangle that underscores the lack of hot-dust emission.
Figure 2: Compare the observed-frame LRD stacks to BHD templates shifted to z≈6.5 and scaled to typical LRD SMBH masses—predicted F770W–F1800W colors are much redder than the LRD data; check the five MIRI-detected LRD points and the overplotted ‘Virgil’ track to see how genuinely hot-dust systems would appear.
Figure 3: Examine LRD bolometric luminosity functions versus pre-JWST quasars and the median BHD Lbol marker to assess number-density and luminosity mismatches that argue against a simple BHD analog picture.

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2508.19618v1

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

Seongjae Kim, Woong-Seob Jeong, Minjin Kim, Hyunsung D. Jun, Yujin Yang, Takao Nakagawa

Theme match 5/5

Digest

Spectro-photometry of the hyperluminous BlueDOG ADFS-KMTDOG-102 (z=2.604) in ADF-S shows an extremely massive, heavily obscured system (log M*=12.3) with SED shape akin to JWST little red dots. Gemini-S GMOS+FLAMINGOS-2 spectra indicate AGN-dominated UV line ratios, a double-peaked, ~2″-extended Lyα, and an extinction-corrected broad Hα giving an enormous black hole (log MBH=10.2). The source thus links DOG-like hyperluminous systems to LRD-like SEDs at cosmic noon, suggesting rapid black-hole growth in a mature stellar host. The blue-excess UV continuum remains unresolved—consistent with either recent star formation or AGN-scattered light, with the Lyα escape fraction sitting near LAE relations.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1: Slit placements over the KMTNet color image—verify that the GMOS slit crosses the nucleus and the off-nuclear blue-excess knot targeted in the B band.
Fig. 2 (left/center): Inspect the double-peaked, spatially extended (~2″) Lyα and note the skyline-contaminated C IV; together they establish AGN-powered UV lines and extended resonant scattering.
Fig. 2 (right): Broad+narrow Hα decomposition used for the MBH estimate; check the [S II] masked region and continuum handling near the FLAMINGOS-2 band edge.
Fig. 3: Best-fit SED components (stellar, AGN with polar dust, and SF-heated dust) demonstrating old-star dominance and the LRD-like SED shape.
Fig. 4: Lyα escape fraction vs E(B−V) placing the object near LAE trends; compare the SFR-derived and AGN-derived cases to gauge the plausibility of scattered-light vs young-star origins.

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2508.21748v1

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

Ignas Juodžbalis, Cosimo Marconcini, Francesco D'Eugenio, Roberto Maiolino, Alessandro Marconi, Hannah Übler, Jan Scholtz, Xihan Ji, Santiago Arribas, Jake S. Bennett, Volker Bromm, Andrew J. Bunker, Stefano Carniani, Stéphane Charlot, Giovanni Cresci, Pratika Dayal, Eiichi Egami, Andrew Fabian, Kohei Inayoshi, Yuki Isobe, Lucy Ivey, Gareth C. Jones, Sophie Koudmani, Nicolas Laporte, Boyuan Liu, Jianwei Lyu, Giovanni Mazzolari, Stephanie Monty, Eleonora Parlanti, Pablo G. Pérez-González, Michele Perna, Brant Robertson, Raffaella Schneider, Debora Sijacki, Sandro Tacchella, Alessandro Trinca, Rosa Valiante, Marta Volonteri, Joris Witstok, Saiyang Zhang

Theme match 4/5

Digest

Strong lensing plus JWST/NIRSpec IFS resolves narrow Hα kinematics and spectroastrometric shifts in the lensed Little Red Dot Abell2744‑QSO1 at z=7.04, enabling a direct rotation curve from ~10–200 pc. The curve is Keplerian and rules out compact extended mass profiles (e.g., MW‑like nuclear star cluster, Plummer, or a DM cusp), implying a central point mass of order 5×10^7 M⊙ consistent with Balmer‑line virial estimates. The inferred stellar content is minimal, with MBH/M* > 2, pointing to a near‑“naked” black hole in a pristine environment. This result validates virial BH masses for LRDs at the EoR and captures a massive BH seed in its earliest growth phase.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1 (narrow Hα maps): Inspect the flux, velocity, and dispersion maps to see the ~200 pc spatial extent, the ~10 km s−1 velocity gradient, and the offset between the broad‑line centroid and the dynamical center—evidence the gradient is real (not slicer PA artefacts).
Fig. 2 (top, rotation curve): Compare binned narrow‑Hα node velocities with the spectroastrometric points; note the strong preference for a point‑mass fit (χR^2≈0.8) over an MW‑like nuclear star cluster (χR^2≈3.8), yielding log MBH/M⊙≈6.94 as a lower limit due to unknown inclination.
Fig. 2 (bottom, residuals): The full 2D MOKA3D fits show far smaller residuals for Keplerian rotation than for extended‑mass models—key visual proof that an NSC/Plummer profile cannot reproduce the field.
Extended Data Fig. 1 (spectroastrometry): The +/−50 km s−1 Hα centroids are separated by 24.9±9.4 pc, implying rspec≈12.5 pc; with FWHM≈52±14 km s−1 this encloses log M/M⊙≈6.90—anchoring the inner mass scale.
Extended Data Fig. 2 (cluster concentration limits): Upper limit Rc≲0.2 pc places any putative NSC >1 dex more concentrated than known NSCs or early star clusters, reinforcing that the mass must be a BH.

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2508.20177v1

MEGA: Spectrophotometric SED Fitting of Little Red Dots Detected in JWST MIRI

Kaila Ronayne, Casey Papovich, Allison Kirkpatrick, Bren E. Backhaus, Fergus Cullen, Lu Shen, Micaela B. Bagley, Guillermo Barro, Steven L. Finkelstein, Kurt Hamblin, Jeyhan S. Kartaltepe, Dale D. Kocevski, Anton M. Koekemoer, Erini Lambrides, Fabio Pacucci, Guang Yang

Theme match 4/5

Digest

MEGA fits JWST/NIRCam+NIRSpec+MIRI SEDs for eight spectroscopically confirmed Little Red Dots at z=5.1–8.7 using CIGALE and Prospector across star-forming, AGN-dominated, and composite scenarios. By BIC, six of eight prefer AGN-dominated solutions, consistent with red F150W–F444W > 1 but flat F444W–F770W and −1.0 < F1000W–F1500W < 1.1 colors that imply weak hot dust. Two Balmer-break LRDs with broad Hα are matched by hot, dense-gas (log T=5–5.7; log n=9–11) plus an added 800–1400 K thermal component, with total Lbol/L_sun < 10^12 and consistency with far-IR/radio limits. However, no single template reproduces all observables—the dense-gas fits miss the rest-UV and narrow [O III]—arguing for non-standard gas conditions and mixed AGN–star-formation.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect NIRCam vs MIRI cutouts and the NIRSpec G395M spectrum of ID 10444 to verify point-like morphology, slit coverage, and the identification/width of Balmer and [O III] lines that motivate AGN-like emission.
Figure 2: Read the F1000W–F1500W vs F444W–F770W and F150W–F444W color–color planes to see that LRDs cluster at flat NIRCam–MIRI colors (weak hot dust), and compare their loci against redshifted SWIRE tracks (Type 2 QSO/torus/SF) to gauge which templates are plausible.
Figure 3: Compare star-forming–only fits (CIGALE vs Prospector) for representative LRDs; look for failures around the Balmer break and mid-IR (F770W–F1500W) where pure stellar models underpredict or mis-shape the SED.
Figure 4: Examine AGN-dominated fits and the decomposition (disk vs torus) to see how flat mid-IR colors constrain the torus and where AGN models better match the SED than SF-only, yet still leave UV/[O III] mismatches.

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2508.18358v1

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

Bingjie Wang, Joel Leja, Harley Katz, Kohei Inayoshi, Nikko J. Cleri, Anna de Graaff, Raphael E. Hviding, Pieter van Dokkum, Jenny E. Greene, Ivo Labbé, Jorryt Matthee, Ian McConachie, Rohan P. Naidu, Erica J. Nelson

Theme match 3/5

Digest

Using recombination lines rather than continuum, the authors analyze uniformly selected RUBIES LRDs plus an 8 hr G395M spectrum of RUBIES‑EGS‑49140 to infer the incident ionizing spectra. They find a strong tension: very large Hα equivalent widths demand abundant H-ionizing photons, yet HeII is only marginally detected with HeII/Hβ ~10^-2, far below local AGN, implying an unusually soft spectrum missing hard photons. Cloudy modeling rules out standard AGN accretion-disk SEDs and favors soft, star-like ionizing fields (e.g., cold disks or AGN+stars composites) and/or high gas/dust optical depths, with HeII remaining an optically thin, robust tracer even in dense neutral hydrogen “black-hole star” envelopes. The HeII-based diagnostic reframes the LRD central-engine debate by highlighting missing hard photons and incident spectra that resemble massive stars.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1: Inspect the stacked RUBIES Prism spectrum around HeII λ4686 and H lines to see the population-level HeII weakness versus strong Hα, establishing the core hard-photon deficit.
Fig. 2: Zoom on HeII for RUBIES‑EGS‑49140 comparing Prism and 8 hr G395M data; evaluate how narrow+broad Gaussian fits and continuum placement still yield a very low HeII EW, quantifying measurement systematics.
Fig. 3: Contrast the SDSS quasar composite with representative LRD spectra and the RUBIES slope distribution; verify that LRD continua are much redder than standard AGN expectations, motivating non-standard SEDs.
Fig. 4: Follow the predicted Hα and HeII EWs versus ionizing-slope/AGN-template grids; locate the LRD median Hα EW and EGS‑49140 points to see the explicit inconsistency between Hα-required hardness and HeII-implied softness.

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2509.00153v1

Quasar Radiative Feedback May Suppress Galaxy Growth on Intergalactic Scales at $z = 6.3$

Yongda Zhu, Eiichi Egami, Xiaohui Fan, Fengwu Sun, George D. Becker, Christopher Cain, Huanqing Chen, Anna-Christina Eilers, Yoshinobu Fudamoto, Jakob M. Helton, Xiangyu Jin, Maria Pudoka, Andrew J. Bunker, Zheng Cai, Jaclyn B. Champagne, Zhiyuan Ji, Xiaojing Lin, Weizhe Liu, Hai-Xia Ma, Zheng Ma, Roberto Maiolino, George H. Rieke, Marcia J. Rieke, Pierluigi Rinaldi, Yang Sun, Wei Leong Tee, Feige Wang, Jinyi Yang, Minghao Yue, Junyu Zhang

Theme match 2/5

Digest

Using JWST/NIRCam grism WFSS from the SAPPHIRES and EIGER programs, the authors map [O III] emitters around the z=6.3 quasar J0100+2802 and analyze 130 sources to test radiative feedback. They find a clear decline in [O III] λ5008-to-UV luminosity (L5008/L1500) toward the quasar over ~8–10 cMpc: L1500 stays flat with distance while L5008 rises away from the quasar, and the trend tracks the projected photoionization-rate profile Γ_qso, with a weaker but consistent signal along the line of sight. The inferred transverse suppression radius implies a recent radiative episode of ~4.5 Myr, favoring rapid H2 photodissociation over slower thermal photoheating as the mechanism. Environmental effects alone cannot reproduce the signal, offering geometry-based constraints on intergalactic quasar feedback and recent quasar lifetimes.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the sky map and LOS inset to see how [O III] emitters near z≈6.3 are distributed around J0100+2802 and how symbol sizes (L5008) vary with distance; note the fore-/background slices for context.
Figure 2: Check the injection–recovery completeness versus transverse distance (50–60% thresholds) and the L5008/L1500–distance trend; compare the fitted decline with the overplotted Γ_qso profile to gauge the radiative origin of the suppression.
Figure 3: Compare the near-QSO, foreground, and background slices; the per-slice fits and CDFs show that only the near-QSO sample exhibits depressed L5008/L1500, while the background overdensity has higher ratios (supported by K–S results).
Figure 4: Contrast L5008/L1500 with local overdensity (negative trend near the QSO vs weak positive in controls) and verify that M1500 shows no distance trend, arguing against environment or UV luminosity as the driver of the suppression.

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2508.21818v1

First constraints on the local ionization topology in front of two quasars at z ~ 7.5

Timo Kist, Joseph F. Hennawi, Frederick B. Davies, Eduardo Bañados, Sarah E. I. Bosman, Zheng Cai, Anna-Christina Eilers, Xiaohui Fan, Zoltán Haiman, Hyunsung D. Jun, Yichen Liu, Jinyi Yang, Feige Wang

Theme match 2/5

Digest

Uses JWST/NIRSpec damping-wing fits and a three-parameter local model to extract the Lorentzian-weighted HI column N_HI^DW, the distance to the first neutral patch r_patch, and the quasar lifetime t_Q in front of two z ≈ 7.5 quasars. J1007+2115 favors a moderately ionized IGM with ⟨x_HI⟩ = 0.32^{+0.22}_{-0.20}, an exceptionally short lifetime log10 t_Q/yr = 4.14^{+0.74}_{-0.18}, r_patch ≈ 28.9 cMpc, and log10 N_HI^DW ≈ 19.70, while J1342+0928 implies a higher neutral fraction ⟨x_HI⟩ = 0.58^{+0.23}_{-0.23}, an intermediate lifetime log10 t_Q/yr = 5.64^{+0.25}_{-0.43}, r_patch ≈ 10.9 cMpc, and log10 N_HI^DW ≈ 20.24. Mapping these local constraints through topology-informed priors links the sightline-level topology to global reionization timing. The N_HI^DW metric also naturally captures potential contributions from foreground absorbers toward J1342+0928.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Compare local vs global fits to J1007+2115 around the Lyα red wing; the amplitude/shape that the local model attributes to N_HI^DW and r_patch is visible in the separation between the absorbed model and reconstructed continuum, with uncertainty bands showing how tightly the red wing is pinned.
Figure 2: Inspect the posteriors for J1007+2115—note the tight preference for a very short t_Q (~10^4.1 yr), large r_patch (~29 cMpc), and low N_HI^DW, and how the topology-informed mapping yields ⟨x_HI⟩ ≈ 0.32 consistent with the direct global fit.
Figure 3: For J1342+0928, the stronger damping wing drives higher N_HI^DW and a nearer first neutral patch (r_patch ~11 cMpc); contrast the inferred continuum and residuals with J1007+2115 to see why the lifetime shifts to an intermediate value.
Figure 4: Posterior comparisons for J1342+0928 including overlays from putative local absorbers; use the N_HI^DW axis to gauge how much of the damping wing could be explained by CGM/IGM absorbers under different metallicity assumptions.