Weekly issue

Week 36, 2025

Sep 1–7, 2025

Week 36, 2025 includes 11 curated papers, centered on high-z, LRD, spectroscopy.

2509.05434v1

What you see is what you get: empirically measured bolometric luminosities of Little Red Dots

Jenny E. Greene, David J. Setton, Lukas J. Furtak, Rohan P. Naidu, Marta Volonteri, Pratika Dayal, Ivo Labbe, Pieter van Dokkum, Rachel Bezanson, Gabriel Brammer, Sam E. Cutler, Karl Glazebrook, Anna de Graaff, Michaela Hirschmann, Raphael E. Hviding, Vasily Kokorev, Joel Leja, Hanpu Liu, Yilun Ma, Jorryt Matthee, Themiya Nanayakkara, Pascal A. Oesch, Richard Pan, Sedona H. Price, Justin S. Spilker, Bingjie Wang, John R. Weaver, Katherine E. Whitaker, Christina C. Williams, Adi Zitrin

Theme match 5/5

Digest

Empirically integrating X-ray–to–far-IR SEDs for two of the most luminous Little Red Dots (A2744-45924 and RUBIES-BLAGN-1), the authors directly measure bolometric luminosities rather than adopting standard AGN corrections. They find that over half of Lbol emerges in the rest-frame optical with Lbol/L5100≈5, while X-ray, UV, and reprocessed mid/far-IR components are sub-dominant, and deep ALMA/MIRI limits rule out a standard dust-reddened AGN SED. New bolometric corrections lower previously inferred luminosities by ~10×, implying BH masses of ~10^5–10^7 Msun (and ~10^8 Msun hosts) if radiating near Eddington and easing tensions with clustering and BH mass density. A key assumption is that far-IR luminosities lie well below current observational limits.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Compare the integrated panchromatic SEDs of A2744-45924 and RUBIES-BLAGN-1 across the shaded X-ray/UV/optical/NIR/IR bands to see that the optical dominates Lbol and that ALMA/MIRI limits exclude a standard Eddington AGN SED scaled to prior assumptions.
Figure 2: Inspect the shift from H-based (and reddening-corrected) Lbol to the new empirical values—an order-of-magnitude drop—and read off the implied BH masses at the Eddington line (~10^5–10^7 Msun).
Figure 3: Look at the updated bolometric luminosity function versus models (DELPHI; Volonteri et al.) and the “maximum” halo line to see how the downward Lbol revision brings LRDs below theoretical ceilings and alleviates prior tensions.

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2509.03576v1

How similar are narrow-line Seyfert 1 galaxies and high-z type 1 AGN?

M. Berton, E. Järvelä, A. Tortosa, C. Mazzucchelli

Theme match 5/5

Digest

Review draws a line between local narrow-line Seyfert 1s and the newly uncovered z>4 type 1 AGN/LRDs: both host low-mass (∼10^6–10^7 M⊙) black holes accreting near or above Eddington and often show features like steep, variable X-rays and, in a subset, relativistic jets. The authors argue jets can help shed angular momentum in super-Eddington flows, making NLS1s practical analogs for early SMBH growth. Radio examples underscore the wide range from host-dominated star-formation morphologies to blazar-like, large-scale jets. Key caveat: some systematic differences remain, plausibly tied to distinct environments and evolutionary paths at high redshift.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1 (J0713+3820): Inspect the patchy 5.2 GHz morphology and spectral-index map to see circumnuclear star-formation–dominated radio emission in an NLS1, illustrating the host-dominated end of the class.
Fig. 2 (J0354−1340): The 5.5 GHz map overlaid on the host shows a southern jet reaching ∼94 kpc projected (∼127 kpc deprojected), demonstrating that some NLS1s launch large-scale, blazar-like jets despite low BH masses.
Fig. 3 (Mrk 783): Compare the very steep-spectrum region SE of the nucleus with the currently active jet to the NE; this juxtaposition highlights aged plasma versus ongoing activity and possible duty-cycle or orientation changes.
Fig. 4 (J1522+3934): The non-simultaneous radio SED with PL/BPL fits reveals variability and spectral breaks, useful for diagnosing jet dominance, spectral aging, and absorption in radio-loud NLS1s.

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2509.02662v1

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

Yilun Ma, Jenny E. Greene, Marta Volonteri, Andy D. Goulding, David J. Setton, Marianna Annunziatella, Eiichi Egami, Xiaohui Fan, Vasily Kokorev, Ivo Labbe, Xiaojing Lin, Danilo Marchesini, Jorryt Matthee, Themiya Nanayakkara, Luke Robbins, Anna Sajina, Marcin Sawicki

Theme match 5/5

Digest

Wide-area imaging over 15.3 deg^2 targets the bright end of little red dots at 4.5<z<4.9 with K<23.7 and finds only one candidate (ECOSMOS-LumLRD-z5, z_phot≈4.6), implying n(M5100<-23.5)≈10^-8 cMpc^-3—about ten times below UV-selected quasars at the same optical luminosity. Combining with JWST-identified LRDs, the optical LF shows a sharp cutoff at λL5100≈2.5×10^44 erg s^-1, whereas the quasar LF turns over at ≳20× higher luminosity. The result confirms LRDs are exclusively low-luminosity rather than quasar counterparts. If the LF shape holds, it favors low-mass black holes accreting within a narrow Eddington-ratio range.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Check that stacked, redshift-shifted LRD spectra matched to K=23.7 mag keep all selection-band photometry above survey depths—this tests volume completeness—and see where ECOSMOS-LumLRD-z5 falls inside the color-selection box versus the full parent catalog.
Figure 2: Compare the photometric SED of ECOSMOS-LumLRD-z5 to the NIRSpec/PRISM spectrum of UNCOVER-45924 to verify the LRD-like V-shaped SED and Balmer-limit turnover; inspect the HST F814W cutout and the EAZY p(z) for robustness of the z_phot≈4.6 solution.
Figure 3: Inspect the LRD optical luminosity function points and upper limit from this work alongside JWST LRDs; note the sharp cutoff near λL5100≈2.5×10^44 erg s^-1 and the contrast with extrapolated quasar LFs at the same epoch.
Figure 4: Use the schematic to see how a low-mass BH population with high, narrowly distributed Eddington ratios can reproduce the observed LRD LF cutoff, in contrast to the broader quasar BH mass/Eddington distributions.

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2509.02027v1

The ALPINE-CRISTAL-JWST Survey: Revealing Less Massive Black Holes in High-Redshift Galaxies

Wenke Ren, John D. Silverman, Andreas L. Faisst, Seiji Fujimoto, Lin Yan, Zhaoxuan Liu, Akiyoshi Tsujita, Manuel Aravena, Rebecca L. Davies, Ilse De Looze, Miroslava Dessauges-Zavadsky, Rodrigo Herrera-Camus, Edo Ibar, Gareth C. Jones, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Yu-Heng Lin, Ikki Mitsuhashi, Juan Molina, Ambra Nanni, Monica Relano, Michael Romano, David B. Sanders, Manuel Solimano, Enrico Veraldi, Vicente Villanueva, Wuji Wang, Giovanni Zamorani

Theme match 5/5

Digest

ALPINE-CRISTAL-JWST uses NIRSpec IFU aperture spectra at photometric peaks in 18 z=4.4–5.7 main-sequence galaxies and finds 7 broad-line AGN candidates via Hα, including one robust source (FWHM ≈ 2800 km/s) and six with 600–1600 km/s, two in a merger. Narrow-line diagnostics place these systems within the star-forming locus, so broad-line detection is the only reliable discriminator; the implied broad-line AGN fraction is 5.9–33% and is aided by targeting high-mass hosts. Virial estimates give MBH ≈ 10^6–10^{7.5} M⊙ with Lbol/LEdd ≈ 0.1–1, and candidates lie at or below the local MBH–M* relation, counter to prior JWST reports of overmassive BHs. The work highlights mass-dependent selection effects and points to a substantial, previously missed population of faint, undermassive broad-line AGN at early times.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (DC_536534): Inspect how the central-aperture extraction isolates a broad Hα component relative to surrounding narrow emission; compare G235M vs G395M line coverage and continuum to gauge BLR detectability.
Figure 2 (pipeline): Follow the decision branches that separate BLR fits from outflow/narrow-only models and note where the 7 candidates pass; this shows which diagnostics actually elevate a source to “broad-line AGN.”
Figure 3 (simulations): Compare how Hα width and visibility change across host mass and Eddington ratio; identify the parameter space where broad lines become distinguishable at the survey’s noise and resolution.
Figure 4 (MBH–M* limits): Check positions of candidates versus local relations and the IFU-center vs full-galaxy detection thresholds; verify why prior JWST AGNs fall above the limits while these systems cluster at or below the local scaling.

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2509.03571v1

Do Little Red Dots Vary?

Amy Secunda, Rachel S. Somerville, Yan-Fei Jiang, Jenny E. Greene, Lukas J. Furtak, Adi Zitrin

Theme match 4/5

Digest

Simulated light curves for little red dots are generated under two variability prescriptions: an empirical sub‑Eddington DRW tuned to low‑z AGN and a radiation‑MHD–motivated super‑Eddington disk model. With today’s 2–4‑epoch JWST sampling, the DRW case would have produced far more rest‑UV/optical variability than is seen, while the super‑Eddington model naturally matches the near‑steady continua. The high‑cadence nexus imaging should yield Δm>1 mag if DRW holds, but only the lowest‑mass LRDs vary appreciably in the super‑Eddington scenario; meanwhile, twinkle spectroscopy is still expected to detect broad‑line variability if soft X‑rays can reach the BLR. Net result: super‑Eddington accretion neatly explains the missing continuum variability while allowing line changes.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Compare PSDs from the super‑Eddington simulations to a sub‑Eddington DRW—note how increasing ˙M suppresses UV/soft‑X variability and how the extrapolated optical PSD sits well below the DRW expectation.
Figure 2: Read off the simulated Δm distributions in F115W and F356W for past JWST/HST cadences vs nexus; see that DRW predicts detectable variability already, while the super‑Eddington tracks largely sit under the current photometric limits.
Figure 3: Inspect the percent broad‑line flux change histograms—only the soft‑X driven super‑Eddington case clears the twinkle detection threshold, highlighting the need for BLR‑reaching soft X‑ray irradiation.
Figure 4: Trend of Δm with black‑hole mass in F356W for nexus cadence—DRW rises above the detectability line broadly, but super‑Eddington variability is only detectable toward the lowest masses, quantifying where continuum changes might appear first.

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2509.03291v1

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

Krisztina Perger, Judit Fogasy, Sándor Frey

Theme match 4/5

Digest

The authors test whether little red dots can be explained as tidal disruption events by confronting 3 GHz stacking-based radio non-detections of LRDs with known TDE radio luminosities and volumetric rates. Converting the VLASS/GOODS-N/COSMOS stacking limits into rest-frame specific luminosities across the LRD redshift range, they find radio-quiet TDEs are fully consistent with the limits, while radio-loud TDEs fit only in restricted redshift–spectral-index regions. Forward-modeling fluxes for representative TDEs (RQ: XMMSL1 J0740−85, ASASSN-14li; RL: Sw J1112.82, Sw J2058+05) and comparing number densities shows that delayed, long-lived radio flares plus cosmological time dilation still keep a TDE origin plausible from the radio point of view. The single radio-detected LRD (PRIMER-COS 3866) also lies within the allowed parameter space.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Map the LRD radio-luminosity space against dashed/dotted contours for RL/RQ TDE exemplars; check where the RL/RQ boundary falls relative to the stacking-based luminosity ceiling and where PRIMER-COS 3866 sits.
Figure 2: For the two template TDEs (Sw J2058+05 and XMMSL1 J0740−85), read off the predicted 3 GHz fluxes versus redshift and spectral index; note which regions would have been excluded by current VLASS/GOODS-N stacking limits and which remain allowed.
Figure 3: Compare LRD volumetric densities to galaxy densities and TDE occurrence-rate curves; assess whether plausible TDE rates (RQ vs RL) can supply the observed LRD numbers as a function of redshift.
Table 1 (implied in text): Note the adopted peak radio luminosities and redshifts of the four comparison TDEs; these anchor the RL/RQ contours used in Figures 1–2.
PRIMER-COS 3866 reference lines (in Figs. 1–2): Verify how the lone radio detection compares to the RL/RQ threshold and stacking limits, testing consistency with an RQ-TDE interpretation.

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2509.03283v1

A two-phase model of galaxy formation: IV. Seeding and growing supermassive black holes in dark matter halos

Yangyao Chen, Houjun Mo, Huiyuan Wang

Theme match 4/5

Digest

Builds a seed-to-SMBH pathway inside a two-phase (fast/slow halo growth) framework: Pop III remnants are bred in mini-halos at the H2- (or delayed atomic-) cooling thresholds, then grow via nuclear-burst super-Eddington episodes, SGC sub-cloud capture, and finally mergers. Implemented on subhalo merger trees, the model produces a broad seed spectrum (10–10^5 Msun at z≈20–30) and a multi-piece, redshift-dependent M_BH–M_* relation set by the dominant channel. A key result is that early nuclear bursts enable rapid mass gain, naturally yielding compact accretors reminiscent of JWST little red dots before merger-dominated quiescence. The framework links LW background and halo assembly rate to BH demographics and matches current constraints.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Use the purple H2-/atomic-cooling and SGC-Jeans bands over halo assembly tracks to read off when/where Pop III collapse and BH seeding occur versus halo mass and growth rate; note how the seeding window shifts with concentration and accretion history.
Figure 2: Schematic connecting LW radiation and dynamical heating to the Pop III IMF and seed ‘flavors’ (CCSN, PISN, DCBH); trace how increasing delay to atomic-cooling raises the dominant-star mass and yields heavier seeds.
Figure 3: Collapse-threshold mass versus LW intensity and specific accretion rate, with simulation markers; inspect how the parameterized bands set the seeding delay and move seeds from H2- to atomic-cooling halos—inputs used in the merger-tree implementation.
Figure 4: Pop III IMFs for different first-star masses and the resulting remnant/seed masses; identify the CCSN–PISN–DCBH transitions that generate the 10–10^5 Msun seed spectrum feeding later growth channels.

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2509.05423v1

Another view into JWST-discovered X-ray weak AGNs via radiative dusty feedback

W. Ishibashi, A. C. Fabian, R. Maiolino, Y. Gursahani, C. S. Reynolds

Theme match 3/5

Digest

The authors revisit the X-ray weakness of JWST-selected AGN by mapping dusty gas dynamics onto the N_H–λ plane using the effective Eddington limit for dust. Varying metallicity, grain size, and composition shifts the critical boundary: low-Z, dust-poor gas resists radiation pressure, enabling long-lived nuclear absorption and heavy X-ray obscuration consistent with early JWST-AGN and LRDs. The blowout vs. stalling analysis shows that higher metallicity is needed to expel larger columns, whereas substantial columns stall at low Z, making metallicity a key regulator of obscuration. The framework also naturally links Balmer absorption features and weak radio emission to the same radiative dusty feedback physics.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1: N_H–λ boundary vs metallicity—inspect how decreasing Z shifts the curve right, shrinking the forbidden (blowout) region and enlarging the long-lived obscuration zone.
Panels varying dust grain size/composition—compare graphite vs silicate and MRN cutoffs to see how UV/IR opacities move the IR- and UV-limited segments of the boundary, and where the single-scattering regime causes overlap at intermediate N_H.
Blowout versus stalling map—read off the Z required to eject given N_H; note the region where N_H ≳ 10^23–10^24 cm^-2 stalls at low Z but is expelled at higher Z.
Application plot placing JWST-AGN/LRDs in the N_H–λ plane—locate typical λ and inferred/required N_H against the long-lived obscuration region to gauge consistency with X-ray non-detections and stacking limits.

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2509.02664v1

Little Red Dots Are Nurseries of Massive Black Holes

Fabio Pacucci, Lars Hernquist, Michiko Fujii

Theme match 3/5

Digest

Assuming the star-only interpretation of compact, red z∼5 Little Red Dots, the authors model ultradense cores where dynamical friction for 10 M⊙ stars in the inner 0.1 pc is <0.1 Myr, triggering rapid mass segregation. A Fokker–Planck core-evolution calculation, an analytic collisional-growth model, and direct N-body simulations all converge on runaway mergers that build a very massive star of 9×10^3–5×10^4 M⊙ within <1 Myr. The VMS then contracts on a ∼8000 yr Kelvin–Helmholtz timescale and collapses to an ∼10^4 M⊙ black hole. This route yields seed number densities above direct-collapse expectations and, with a dense residual core, can power elevated tidal disruption event rates.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Track the steepening of the central density and the four-order-of-magnitude mass gain inside the central parsec to see explicit core collapse while the outer profile remains static.
Figure 2: Compare pre/post-contraction dynamical friction times; the fall to <0.1 Myr in the inner 0.1 pc explains rapid mass segregation, while the rise in σ1D quantifies the collisional environment.
Figure 3: Read the VMS mass growth curve against the accretion and loss rates to see when net growth becomes runaway and why the final M_VMS is reached on a timescale comparable to the central t_df.
Figure 4: Use the N-body track—initial discrete mergers followed by a runaway phase completing within <1 Myr—to confirm the analytic prediction and visualize the stepwise assembly of the VMS.

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2509.01674v1

Understanding the Evolution of Black Hole Accretion and Dust out to z=4 with a Deep Imaging Extragalactic Survey with PRIMA

Andreas L. Faisst, Chian-Chou Chen, Laure Ciesla, Carlotta Gruppioni

Theme match 3/5

Digest

This Concept/Survey paper lays out PRIDES, a 1.6 deg^2 COSMOS-field program with PRIMA to fill the mid‑IR gap (24–240 μm) between JWST and ALMA and trace dust and black‑hole growth out to z≈4. With hyperspectral imaging and spectroscopy, PRIDES will constrain IR SED shapes, dust temperatures, and obscured SFRs while identifying dust‑obscured AGN via PAH and silicate features, detecting mid‑IR emission even beyond z>3. Simulations indicate photometric redshifts from PAH features with accuracy that degrades as the AGN contribution increases, and silicate strengths track AGN hardness. Together, these data will map the fraction of obscured star formation and the prevalence of buried SMBH accretion across environments in COSMOS.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Check which PAH and silicate rest‑frame windows PRIMA samples at z≈1–4 to see how it truly bridges JWST and ALMA and what diagnostics become accessible at each redshift.
Figure 2 (left): Read the PRIDES depth curves against Kirkpatrick SED templates and compare to CHAMPS/(Ex)MORA, SCUBA‑2, NIKA2, and legacy Spitzer/Herschel limits to gauge what L_IR and stellar‑mass regimes are newly reachable.
Figure 2 (right): Inspect the simulated Band‑1 spectra for 0% vs 80% AGN to see how silicate absorption/emission shifts the continuum and features, setting PRIMA’s leverage on obscured AGN fraction.
Figure 3: Note the PRIDES footprint relative to COSMOS‑Web and HST/ACS to understand synergy and the range of environments (voids to overdensities) sampled for dust/AGN demographics.
Figure 4: Examine how PAH‑based redshift precision varies with L_IR and AGN fraction to judge redshift reliability for dusty and AGN‑dominated sources.

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2509.05417v1

The Light Echo of a High-Redshift Quasar mapped with Lyman-$α$ Tomography

Anna-Christina Eilers, Minghao Yue, Jorryt Matthee, Joseph F. Hennawi, Frederick B. Davies, Robert A. Simcoe, Richard Teague, Rongmon Bordoloi, Gabriel Brammer, Yi Kang, Daichi Kashino, Ruari Mackenzie, Rohan P. Naidu, Benjamin Navarrete

Theme match 2/5

Digest

Deep JWST/NIRSpec MSA spectroscopy of twelve background galaxies behind the z_QSO ≈ 6.3 quasar J0100+2802 yields the first spectroscopic Lyα-tomography map of a quasar “light echo” in the transverse direction. Clear excess Lyα transmission at the quasar’s systemic redshift appears along multiple sightlines, enabling a 3D reconstruction of the ionized bubble and its ionization-cone orientation/inclination, and setting f_obsc < 91%. Modeling the light-travel geometry implies a UV-on timescale t_QSO = 10^{5.6+0.1}_{-0.3} yr (≈2–5×10^5 yr), far shorter than required for continuous thin-disk growth to the observed SMBH mass. This disfavors purely geometric obscuration as the sole cause of short lifetimes and points to radiatively inefficient or initially enshrouded accretion phases in early SMBH growth.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Use the [O III]-emitter catalog and F115W magnitudes/SNR vs. redshift to see which background sightlines were prioritized and the continuum quality that underpins Lyα-forest transmission measurements.
Figure 2: Inspect the two example 2D/1D spectra where the transverse proximity effect is most obvious at the quasar systemic redshift; note the [O III]-based galaxy redshifts and the continuum power-law fits used to derive Lyα transmission/optical depth.
Figure 3: Compare the ten additional galaxy spectra to assess how consistently the transmission spike at z_QSO recurs across independent sightlines and how its strength varies, informing the inferred cone geometry.
Figure 4: Check the stacked 2D and continuum-normalized 1D spectra centered on z_QSO to verify the ensemble detection of enhanced Lyα transmission and its spatial/velocity extent used in the light-echo modeling.