654 indexed papers · 430 research notes

Research archive

2025-06-13 · 2506.12141v1

A big red dot at cosmic noon

Federica Loiacono, Roberto Gilli, Marco Mignoli, et al.

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JWST reveals BiRD, a luminous little red dot at z=2.33 in the J1030 field, flagged as a bright outlier in the F200W−F356W vs F356W diagram. NIRCam/WFSS detects He I λ10830 and Paγ with both narrow and broad components (FWHM ≳ 2000 km s−1), plus a blueshifted He I absorption indicating dense outflowing gas with N(He I*, 2^3S) ≈ 0.5–1.2×10^14 cm−2 at Δv ≈ −830 km s−1; the source lacks X-ray and radio emission. The Paγ broad component implies MBH ≈ 10^8 M⊙ and Lbol ≈ 2.9×10^45 erg s−1, echoing GN-28074 and RUBIES-BLAGN-1 where similar He I absorption is seen. A first JWST-based census places the LRD space density at z<3 within a factor ∼2–3 of UV-selected quasars at comparable Lbol and MBH, arguing that LRDs contribute meaningfully to AGN demographics at cosmic noon and may trace rapid seed growth.

LRD broad-line AGN spectroscopy outflows demographics BH seeds

2025-06-13 · 2506.12124v1

JWST IFU observations uncover host galaxy continua in extremely red and obscured quasars

Yu-Ching Chen, Nadia L. Zakamska, Andrey Vayner, et al.

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JWST/NIRSpec IFU datacubes of six extremely red quasars at z=2.4–2.9 plus two lower‑z dust‑obscured quasars are decomposed across wavelength to isolate host‑galaxy continua and morphologies. The hosts are compact (Re = 1.4–2.9 kpc) with stellar masses 10^10.6–10.9 Msun, and many targets show quasar–host centroid offsets of 0.4–1.3 kpc suggestive of post‑merger dynamics or patchy obscuration. ERQs sit 0.5–2 dex above the local MBH–M* relation and appear more compact, lower‑n, and lower‑mass than HST‑based inferences, underscoring the leverage of IFU‑based continuum separation. The authors note that the apparent over‑massive black holes may reflect selection bias.

obscured AGN QSO spectroscopy overmassive BH

2025-06-06 · 2506.06418v1

The Identification of Two JWST/NIRCam-Dark Starburst Galaxies at $z=6.6$ with ALMA

Fengwu Sun, Jinyi Yang, Feige Wang, et al.

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Two extreme, dust-enshrouded starbursts at z=6.6 are identified in ASPIRE quasar fields: they are bright in ALMA 1.2 mm continuum and [C II] 158 µm, yet essentially disappear in JWST/NIRCam (F356W >28 AB). SEDs anchored to ALMA fluxes imply heavier obscuration than Arp 220 and star formation rates of ≃80–250 M⊙ yr⁻¹. Their inferred star-formation histories make them plausible progenitors of massive quiescent galaxies at z≳4 and descendants of UV-luminous z>10 systems, with an abundance as high as n≈10⁻⁵⋅⁵ Mpc⁻³ under a light halo-occupation model (~30% of those comparison populations). A key caveat is that number densities come from quasar-companion fields; analogous z∼8 systems may remain undetected (“JWST-dark”) at current survey depths.

2025-06-05 · 2506.05459v1

RUBIES: A Spectroscopic Census of Little Red Dots; All V-Shaped Point Sources Have Broad Lines

Raphael E. Hviding, Anna de Graaff, Tim B. Miller, et al.

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RUBIES delivers uniform NIRSpec PRISM+G395M spectroscopy for ~1500 z>3.1 sources, identifying 80 broad-Balmer emitters, including 28 (35%) at z>6. A coherent subpopulation of 36 shows v-shaped UV–to–optical continua with dominant rest‑optical point sources; these are defined as spectroscopic LRDs, the largest such sample to date. The key result is that every v‑shaped point source exhibits broad Balmer lines, tying continuum shape, compact morphology, and AGN kinematics together. Photometric LRD searches recover only 50–62% of these to F444W<26.5, implying current color cuts miss many due to faint rest‑UV, comparatively bluer rest‑optical colors, or uncertain photo‑z.

LRD broad Balmer v-shaped SED spectroscopy demographics high-z

2025-06-04 · 2506.04350v1

JWST Insights into Narrow-line Little Red Dots

Zijian Zhang, Linhua Jiang, Weiyang Liu, et al.

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Using NIRSpec medium/high-resolution data and line-free photometry, the authors isolate five narrow-line LRDs at z≈5 (H-alpha FWHM ≈250 km/s; one ≈475 km/s) from 32 LRDs with H-alpha coverage, and show that about 20% of color-selected LRD candidates fake a V-shape continuum via strong lines. Relative to normal star-forming galaxies, these objects have higher H-alpha widths and luminosities but smaller equivalent widths. SED fits allow either dusty, compact, high-M* and high-SFR galaxies or low-mass AGN with MBH≈10^5–10^6 Msun, plausibly in an early, super-Eddington phase; the BHs are slightly overmassive vs MBH–M* yet consistent/undermassive vs MBH–sigma and MBH–Mdyn within large errors. Nearly half of high‑z broad-line AGN show V‑shape SEDs, underscoring that LRD-like photometry does not uniquely imply broad-line activity.

LRD spectroscopy v-shaped SED super-Eddington overmassive BH high-z

2025-06-04 · 2506.04004v1

Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions

María Carranza-Escudero, Christopher J. Conselice, Nathan Adams, et al.

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Builds a 124-object little red dot sample at z≈3–10 from CEERS, NEP‑TDF, JADES, and JEMS, then tests SED fits with and without AGN components using BIC. Despite lower χ² when adding AGN templates, BIC generally prefers non‑AGN SEDs, especially when MIRI photometry is included. KS tests of projected environments show LRDs occupy sparser neighborhoods than comparison galaxies, and abundance matching yields conservative halo-mass upper limits. Together these point to most LRDs being compact galaxies or forming star clusters rather than AGN‑dominated, while allowing for a mixed population.

LRD demographics high-z

2025-06-03 · 2506.03244v1

Cosmic Outliers: Low-Spin Halos Explain the Abundance, Compactness, and Redshift Evolution of the Little Red Dots

Fabio Pacucci, Abraham Loeb

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Proposes that Little Red Dots are the visible outcomes of galaxies forming in the extreme low-spin tail of the halo angular-momentum distribution, using Mo–Mao–White scaling to link halo spin to compact disk sizes. Assuming progenitors in the lowest ~1% of spins at z ~ 5 reproduces both the observed number densities and compact effective radii of ~80–300 pc, without requiring a choice between BH- or star-dominated power. The observed redshift trend arises from the competition between an increasing compact-halo fraction and cosmological surface-brightness dimming, yielding an “LRDs Era” at 4 < z < 8; at z < 4 they are bright but rare, while at z > 8 they are common but faint. Agreement with current counts, plus excess small-scale clustering and spectral signs of extreme core densities, supports the low-spin origin.

LRD simulation compact red high-z demographics

2025-06-03 · 2506.03130v1

AGNBoost: A Machine Learning Approach to AGN Identification with JWST/NIRCam+MIRI Colors and Photometry

Kurt Hamblin, Allison Kirkpatrick, Bren E. Backhaus, et al.

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Introduces AGNBoost, an XGBoostLSS framework that ingests NIRCam+MIRI magnitudes, colors, and color-squared terms to jointly predict the mid-IR AGN power-law fraction (frac_AGN) and photometric redshift, trained on 10^6 CIGALE-simulated galaxies. On idealized mocks it attains low scatter (RMSE 0.045 in frac_AGN; NMAD 0.004 in z) with 1.63% and 0.15% outliers, remaining robust under realistic photometric errors (outliers ≈4.38% and 3.35%). It generalizes to empirical templates (recovering 92.6% of AGN with frac_AGN>0.3 and 100% with >0.5) and, on MEGA sources with spectroscopic redshifts, achieves σ_NMAD ≈ 0.056 with 19.79% outliers while yielding frac_AGN consistent with CIGALE (RMSE 0.178; 11.96% outliers). Fast retraining and easy band augmentation make it practical for wide-area JWST catalogs needing rapid AGN screening and photo-zs.

2025-06-03 · 2506.03121v1

EIGER VII. The evolving relationship between galaxies and the intergalactic medium in the final stages of reionization

Daichi Kashino, Simon J. Lilly, Jorryt Matthee, et al.

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Using the full EIGER program, the authors assemble 948 [O III]λ5008 emitters (−21.4≲MUV≲−17.2) at 5.33<z<6.97 from deep NIRCam 3.5 μm slitless spectroscopy along six quasar sightlines and cross-correlate them with Lyα/Lyβ transmission in high-resolution quasar spectra. They find a strong redshift evolution: overdense regions at z<5.50 show suppressed transmission and excess absorption within ~8 cMpc, while at 5.70<z<6.15 the transmission is enhanced on intermediate (~5–20 cMpc) scales, with a transitional regime between. Mock catalogs without galaxy–IGM coupling show these signals are unlikely by chance. The results support inside-out reionization, where local radiation around clustered galaxies dominates early and is later overtaken by a rising UV background that sets the IGM ionization state.

reionization spectroscopy high-z

2025-06-02 · 2506.02289v1

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

Lizhong Zhang, James M. Stone, Patrick D. Mullen, et al.

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Exascale AthenaK GRRMHD simulations solve full radiation transport to survey stellar-mass black hole accretion from sub- to highly super-Eddington, spanning spins and initial magnetic topologies. Super-Eddington runs build geometrically thick, radiation-supported disks with a narrow inner funnel, drive powerful equatorial outflows, and remain radiatively inefficient; near/sub-Eddington structure hinges on net vertical flux—forming a thin dense midplane plus magnetically dominated corona when present, versus magnetically dominated throughout without it. Even short of MAD, net-flux high-spin cases launch relativistic jets, connecting to ULXs (Cyg X-3, SS433) and offering a framework for interpreting JWST little red dots. Caveat: results use simplified opacities tailored to stellar-mass systems.

simulation super-Eddington outflows X-ray

2025-05-30 · 2505.24308v1

Inferring Obscured Cosmic Black Hole Accretion History from AGN Found by JWST/MIRI CEERS Survey

Cheng-An Hsieh, Tomotsugu Goto, Chih-Teng Ling, et al.

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Builds the obscured black hole accretion history from CEERS MIRI sources whose AGN components are identified via CIGALE SED fitting, then converts accretion power and MIR luminosity functions into BHAD across 0<z<4.25. By summing BHARs for composites+AGNs and by integrating LFs (modified Schechter and double power law) down to 1e7 L_sun—two orders fainter than pre-JWST—the authors find BHAD peaking at z≈1–2 (ρ_Ldisk, DPL) or z≈2–3 (modified Schechter). At z≈3 their MIR-inferred BHAD lies above X-ray estimates, hinting at obscured growth missed in X-rays. The new depth strengthens the census of faint, dusty accretion, though the z≈3 excess is within current uncertainties and awaits larger samples.

obscured AGN JWST AGN demographics X-ray

2025-05-28 · 2505.22600v1

Dust Budget Crisis in Little Red Dots

Kejian Chen, Zhengrong Li, Kohei Inayoshi, et al.

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Re-assessing LRD dust, the authors forward-model UV–IR SEDs across multiple extinction laws and dust geometries, then demand consistency with JWST/MIRI, Herschel, and ALMA fluxes and limits. They find A_V ≲ 1.0–1.5 mag under an SMC law for A2744-45924, RUBIES-BLAGN-1, and stacked LRD SEDs, with only slightly weaker bounds for gray UV extinction. These moderate extinctions alleviate the “dust budget crisis” for hostless/low-mass systems and imply ≈10% radiative efficiencies, easing Sołtan-argument tension. The work predicts testable far-IR reprocessed spectra, reframing early black-hole growth pathways for LRDs.

2025-05-28 · 2505.22567v1

A black hole in a near-pristine galaxy 700 million years after the Big Bang

Roberto Maiolino, Hannah Uebler, Francesco D'Eugenio, et al.

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JWST/NIRSpec-IFS dissects the triply imaged Little Red Dot Abell2744-QSO1 at z=7.04, isolating the narrow Hβ to map line ratios. [OIII]5007 is exceptionally weak—[OIII]/Hβn ≈ 0.6 within r<150 pc and <0.32 at 150–300 pc—implying Z ≈ 8×10^-3 Z⊙ centrally and Z<6×10^-3 Z⊙ in the extended gas, while broad Balmer lines/variability yield MBH ≈1.5×10^7 M⊙ in a host with Mdyn ≈10^7.1–10^8 M⊙. This places a massive black hole in an almost pristine, very low-mass galaxy only ~700 Myr post-Big Bang. The chemistry and mass budget strain heavy-seed or super‑Eddington growth paths, motivating alternatives such as primordial black-hole seeds that remain to be fully tested.

LRD high-z BH seeds overmassive BH spectroscopy broad Balmer

2025-05-27 · 2505.20821v1

A candidate for True Type-2 AGN without hidden central BLRs Identified by central Tidal Disruption Event

Gu Ying, Zheng Qi, Cheng Peizheng, et al.

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Reports SDSS J233454.07+145712.9 as a candidate true type‑2 AGN uncovered via a central TDE singled out in 20‑year optical light curves (CSS/PTF/PanSTARRS/ZTF), with a 2009–2013 outburst showing the steep‑rise/smooth‑decline template and otherwise quiescent behavior. TDE modeling (TDEFIT/MOSFIT) favors disruption of a 4.7 Msun main‑sequence star by a 1.17×10^7 Msun black hole, implying an unobscured line‑of‑sight to within ≈20 light‑days of the nucleus. Spectroscopy shows only narrow lines and BPT AGN classification; hypothetical broad Balmer components yield virial masses inconsistent with M–sigma at >6σ, disfavoring hidden BLRs. Together this positions SDSS J2334 as a TT2AGN candidate and demonstrates TDE flares as a practical route to identify BLR‑less nuclei among type‑2 spectra.

obscured AGN variability spectroscopy low-z

2025-05-26 · 2505.20439v1

The Properties of Little Red Dot Galaxies in the ASTRID Simulation

Patrick LaChance, Rupert A. C. Croft, Tiziana Di Matteo, et al.

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Using the ASTRID cosmological simulation, the authors generate mock NIRCam-like views at z=5–8 and identify 17 systems that meet little red dot color-plus-size cuts. These ASTRID LRDs are massive, compact, and dusty—log(M*/Msun)≥9.7, log(MBH/Msun)≥6.8, r_half,*=325–620 pc, with F444W attenuation >1.25—and are bright at F444W=23.5–25.5. Their recent quenching and a dust-obscured AGN produce a steep rest-optical red slope while UV light is star-dominated, pointing to an AGN-feedback-driven miniquenching phase. Lower-mass/fainter galaxies lack sufficient central dust, and many highest-Eddington BH hosts are not LRDs because high SFRs and low attenuation yield flatter spectra; the paucity of low-mass LRDs may partly reflect limited resolution.

LRD simulation obscured AGN compact red high-z

2025-05-26 · 2505.20393v1

NEXUS: A Spectroscopic Census of Broad-line AGNs and Little Red Dots at $3\lesssim z\lesssim 6$

Ming-Yang Zhuang, Junyao Li, Yue Shen, et al.

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Using NIRCam/WFSS F322W2+F444W in the central 100 arcmin² of NEXUS, the team secures a spectroscopic census of 23 BLAGNs at 3≲z≲6, 15 of which satisfy Little Red Dot criteria. The sample spans L(Hα)≈10^{42.2}–10^{43.7} erg s⁻¹, M_BH≈10^{6.3}–10^{8.4} M_⊙, and λ_Edd≈0.1–1 (median 0.4); about half of the LRDs show strong Balmer absorption indicating dense gas near the emission region. Most LRDs reveal extended (hundreds of parsec) rest-UV/optical host emission that significantly or dominantly contributes to the UV, explaining the characteristic UV upturn, and the LRD number density is ≈10⁻⁵ cMpc⁻³ with a mild decline toward lower z. Small-scale (≲1 cMpc) cross-correlations give a BLAGN bias of ~3.3 and halo masses of a few×10¹¹ h⁻¹ M_⊙, while LRD clustering appears overly strong for their space density, hinting at excess small-scale clustering; the single-epoch M_BH and λ_Edd carry large systematics.

LRD broad-line AGN spectroscopy broad Balmer demographics high-z

2025-05-24 · 2505.18873v1

An upper limit of 10$^6$ M$_\odot$ in dust from ALMA observations in 60 Little Red Dots

Caitlin M. Casey, Hollis B. Akins, Steven L. Finkelstein, et al.

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ALMA Band-6 (1.3 mm) continuum follow-up of 60 of the reddest and brightest COSMOS-Web little red dots—preselected with MIRI F770W detections—finds no individual detections and a non-detection in the stack. The data reach a mean σ_rms≈22 μJy, with a stacked flux of S_1.3mm=2.1±2.9 μJy, implying 3σ limits of Mdust<10^6 M⊙ and Ldust≲10^11 L⊙, about 10× deeper than previous submm stacks. These results disfavor large, cold dust reservoirs in typical LRDs. They are consistent with compact, modest dust columns (A_V~2–4) or extreme Balmer breaks from very dense gas (n>10^9 cm^-3) enshrouding a central black hole.

2025-05-21 · 2505.15923v1

Discovery and characterization of 25 new quasars at 4.6 < z < 6.9 from wide-field multi-band surveys

Silvia Belladitta, Eduardo Bañados, Zhang-Liang Xie, et al.

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Targeted optical/IR/radio selections across wide-area surveys yield 25 new luminous quasars at 4.6<z<6.9 (six at z≥6.5; M1450 −25.4 to −27.0), plus new spectra for six independently discovered z>6.5 sources. Three are strong radio emitters, including a z=4.71 object with blazar-like traits (flat spectrum, radio-loudness ~1000, multi-frequency variability) and an SRG/eROSITA X-ray detection (f0.2–2.3 keV ≈1.3×10^−13 erg s^−1 cm^−2). NIR spectroscopy for seven 6.3<z<6.9 quasars gives MgII-based black hole masses of 10^8.58–10^9.14 Msun and Eddington ratios 0.74–2.2, with one source showing an extreme CIV–MgII velocity offset of ~9000 km s^−1. The sample also includes three HiBALs, one with a potential 48,000 km s^−1 outflow, expanding the rare jetted/outflowing quasar census that constrains early SMBH growth and feedback.

QSO luminous quasar high-z spectroscopy radio outflows

2025-05-20 · 2505.14768v1

X-ray properties of massive compact relic galaxies

Orsolya E. Kovacs, Norbert Werner, Akos Bogdan, et al.

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Chandra and XMM-Newton data are used to map hot atmospheres around seven local compact ellipticals selected as red‑nugget analogs, probing BH–bulge–halo coupling. Only MRK 1216 and PGC 32873 show luminous, spatially extended halos enabling radial thermodynamic profiles, with MRK 1216’s RGS spectrum hinting at super‑solar α/Fe. The others have faint or undetected halos, several instead showing AGN‑like power‑law emission. On galaxy scaling planes, cEGs follow a slightly steeper M⋆–LX and sit on the lower edge of M⋆–Mvir, implying red nuggets—and possibly their LRD progenitors—host a diverse range of halo atmospheres.

X-ray compact red low-z

2025-05-20 · 2505.14676v1

A JWST View of the Overmassive Black Hole in NGC 4486B

Behzad Tahmasebzadeh, Matthew A. Taylor, Monica Valluri, et al.

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Using JWST/NIRSpec IFU stellar kinematics plus archival long-slit data, the authors model the compact elliptical NGC 4486B and resolve a double nucleus with a velocity-dispersion peak offset from the photometric center. Axisymmetric Schwarzschild modeling of the full LOSVD yields M_BH = 3.6 ± 0.7 × 10^8 M_sun and a host ratio M_BH/M_* ≈ 4–13%, firmly placing the black hole in the overmassive regime. Dark matter within 1 kpc is weakly constrained (M_DM/M_* < 0.5), and the inferred M_BH is unchanged with or without a halo. The system’s location deep in Virgo supports a stripped-core origin, with the caveat that non-equilibrium double-nucleus dynamics are not modeled, so the mass may be a lower limit.

overmassive BH spectroscopy low-z

2025-05-20 · 2505.14025v1

Quasar identifications from the slitless spectra: a test from 3D-HST

Yuxuan Pang, Xue-Bing Wu, Yuming Fu, et al.

Pang et al. build a slitless-spectrum QSO selector on 3D-HST/G141 by first flagging >6,000 sources with apparently broad lines and then using forward modeling to test whether the “broad” features require a point-like QSO component rather than size-broadened ELG lines. Calibrated on known QSOs, ELGs, and simulations, the criterion recovers ~90% of point-like QSOs with Hα/Hβ while keeping ELG contamination at ~5%. Applied to clean emission-line sources, it yields 19 QSO candidates at z=0.12–1.56 (12 X-ray detections) with broader UV colors and redder optical slopes than SDSS QSOs and MBH≈10^6.9–10^8.3 M⊙, consistent with normal QSOs rather than little red dots. The method boosts QSO completeness at z≈0.8–1.6 in 3D-HST and is directly portable to Euclid and CSST slitless surveys.

QSO spectroscopy broad-line AGN X-ray low-z

2025-05-19 · 2505.12719v1

Composite spectrum of Little Red Dot from a standard inner disk and an unstable outer disk

Chenxuan Zhang, Qingwen Wu, Xiao Fan, et al.

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Builds SEDs for 29 broad-line LRDs and finds uniformly V-shaped continua with a narrow break around ν_b ≃ 10^{14.96±0.06} Hz (λ ≈ 2600–3800 Å). Models the SEDs as a composite of an inner standard thin disk plus an outer gravitationally unstable disk (Q≈1) that self-regulates to T≈2000–4000 K, naturally producing the near-IR/optical bump without invoking extreme dust. MCMC fits anchored by MBH from broad lines reproduce individual SEDs, including UNCOVER 25119 and PRIMER 33823 (whose MIRI 4.9–27.9 μm points trace the bump). Allowing for dense gas to explain strong Balmer breaks suppresses intrinsic optical–UV by only ≲2–3×, implying most LRDs are sub-Eddington and intrinsically weak.

LRD v-shaped SED broad-line AGN spectroscopy high-z

2025-05-14 · 2505.09703v1

SCUBADive II: Searching for $z>4$ Dust-Obscured Galaxies via F150W-Dropouts in COSMOS-Web

Sinclaire M. Manning, Jed McKinney, Katherine E. Whitaker, et al.

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SCUBADive II systematically compiles 60 F150W-dropout, far-IR–bright galaxies in COSMOS-Web by cross-matching JWST non-detections at 1.5 μm with SCUBA-2 and ALMA counterparts, motivated by the benchmark AzTECC71. A core subset of 16 AzTECC71-like sources shows faint F444W (>24 mag) and no COSMOS2020 IDs. SED fits give ⟨SFR⟩=550+500−360 M⊙ yr⁻1 and ⟨log10(M⋆)⟩=11.2+0.5−0.4, with offsets indicating they are not unusually elevated above the star-forming main sequence. Crucially, such heavily obscured systems constitute roughly 20% across mass bins and could account for up to 60% of the z>4 high-mass end (log10 M⋆>11), quantifying a major, previously missed component of the early galaxy census.

ALMA/mm high-z demographics

2025-05-14 · 2505.09669v1

Chandra Rules Out Super-Eddington Accretion Models For Little Red Dots

Andrea Sacchi, Akos Bogdan

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Stacks Chandra data for 55 JADES/NGDEEP-selected little red dots in the 7 Ms CDF-S, reaching ~390 Ms effective exposure, yet finds no soft- or hard-band signal. The resulting flux limits translate to bolometric luminosities more than an order of magnitude below those inferred from JWST, directly ruling out current super-Eddington SED models tailored for LRDs. The non-detections are instead consistent only with extreme obscuration, requiring NH ≳ 10^25 cm^-2. The authors therefore argue the SMBHs in LRDs are likely less massive and/or less luminous than currently claimed.

LRD X-ray obscured AGN super-Eddington high-z

2025-05-14 · 2505.09542v1

A weak Ly$α$ halo for an extremely bright Little Red Dot: Indications of enshrouded SMBH growth

Alberto Torralba, Jorryt Matthee, Gabriele Pezzulli, et al.

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Deep VLT/MUSE mapping around the ultra-luminous LRD A2744-45924 (z=4.464, μ=1.8; L_Hα≈10^44 erg s^-1) reveals a modest, spatially offset Lyα halo with exponential scale length ≈5.7 pkpc and a narrow line (FWHM 270±15 km s^-1) whose flux is only 7% of Hα. Compact N IV] λ1486 coincides with the point-like Hα seen by JWST, while the far-UV continuum centroid shifts with the Lyα offset. The authors argue Hα traces the AGN whereas Lyα is powered by star formation; four neighboring Lyα halos (Δz<0.02, Δr<100 pkpc) show no luminosity excess indicative of AGN illumination. Altogether this points to a dense, near-unity covering-factor cocoon that shrouds the SMBH, suppressing UV/ionizing escape and signaling enshrouded early black-hole growth.

LRD obscured AGN spectroscopy broad Balmer high-z

2025-05-13 · 2505.08885v1

XMM-Newton Conclusively Identifies an Active Galactic Nucleus in a Green Pea Galaxy

Peter G. Boorman, Jiří Svoboda, Daniel Stern, et al.

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Deep XMM-Newton monitoring of the Green Pea SDSS J082247.66+224144.0 (z=0.216) tests for an elusive low-luminosity AGN long hinted by its Γ≈2, L2–10 keV≈10^42 erg s^-1 spectrum. Across 6.2 years (rest-frame), the hard 2–10 keV luminosity remains stable while the soft 0.5–2 keV flux drops by ~60%, yielding a markedly harder second epoch. Swapped-epoch spectral posterior checks and SDSS line decomposition (requiring a broad Hα despite BPT star-forming narrow lines) point to transient, low-column obscuration as the only viable explanation. This work delivers the first conclusive X-ray AGN identification in a Green Pea, strengthening the case that faint AGN could have contributed to reionisation and clarifying local analogs of JWST Little Red Dots.

X-ray low-z obscured AGN variability broad Balmer reionization

2025-05-13 · 2505.08870v1

Galaxies in the Epoch of Reionization Are All Bark and No Bite -- Plenty of Ionizing Photons, Low Escape Fractions

Casey Papovich, Justin W. Cole, Weida Hu, et al.

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Using JWST imaging plus NIRSpec/prism spectra for hundreds of galaxies at 4.5<z<9 from JADES and CEERS, the authors fit joint stellar+nebular SEDs with f_esc as a free parameter to infer both ξ_ion and the ionizing escape fraction. They find ξ_ion rises toward higher redshift and fainter UV luminosity with ~0.3 dex scatter, while the population-averaged escape fractions remain low: ⟨f_esc⟩ ≈ 2.6±1.4% at 6<z<9 and 6.5±2.2% at 4.5<z<6, with little evolution. Propagating these distributions through reionization models yields x_e≈0.5 at z≈5.3–5.8 for M_UV<−16 (possibly late vs. QSO constraints), but consistent timing (x_e≈0.5 at z≈6.0–8.1) once galaxies down to M_UV<−14 are included. Bottom line: EoR galaxies make plenty of ionizing photons, yet low f_esc—likely tied to dense gas and bursty SFHs—keeps most of them trapped.

reionization high-z spectroscopy demographics

2025-05-12 · 2505.07749v1

Emission Line Diagnostics for IMBHs in Dwarf Galaxies: Accounting for BH Seeding and ULX Excitation

Chris T. Richardson, Jordan Wels, Kristen Garofali, et al.

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Builds a multi-wavelength photoionization grid that co-models IMBH accretion and ULX populations in metal-poor, highly star-forming dwarfs, with BH mass tied to seeding channel and metallicity and ULXs evolving with post-starburst age and Z. Finds broadband X-rays and common UV lines carry little leverage on MBH and cannot reliably separate ULXs from IMBHs, while many optical diagrams also fail. Redefines optical cuts using He II λ4686 and [O I] λ6300, and highlights mid-IR ratios (e.g., [Ar II] 6.98μm, [Ne V] 14.3μm, [O IV] 25.9μm) as the cleanest discriminants with sensitivity to MBH and fAGN. Implication: relying on strong-line diagrams alone biases dwarf AGN demographics and may inflate claims of over-massive BHs in some JWST-selected high-z samples.

BH seeds simulation spectroscopy X-ray

2025-05-11 · 2505.06965v1

Black Hole Envelopes in Little Red Dots

Daisaburo Kido, Kunihito Ioka, Kenta Hotokezaka, et al.

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Proposes that little red dots host super-Eddington black holes wrapped in a massive, optically thick envelope that gravitationally confines otherwise destructive winds, effectively making outflows a no-go. The envelope radiates near the system Eddington limit with a photosphere at 5000–7000 K, naturally producing the red optical continuum and the hallmark V-shaped SED while explaining weak X-ray/radio and low short-term variability. A sustained ISM infall of ~1 M_sun/yr feeds the envelope, and a photospheric radius ~0.01 pc sets year-scale variability, linking LRD nuclear structure to Hayashi-limit physics. The envelope both regulates feedback and provides a reservoir enabling rapid early BH growth.

LRD stellar envelope v-shaped SED super-Eddington variability high-z

2025-05-09 · 2505.06359v1

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

Mengtao Tang, Daniel P. Stark, Adèle Plat, et al.

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Deep NIRSpec R=2700 spectroscopy of 53 new z>4 galaxies, plus a census of 851 archival spectra, is used to track high-ionization UV lines. The team reports narrow NV λ1240 in two systems—CEERS‑7902 (z=6.98; an LRD with broad Hβ) and CEERS‑1025 (z=8.72; narrow-line)—while CIV and He II are absent, yielding extreme NV/CIV and NV/He II. The inferred incidence of narrow high-ionization UV lines is 12.5(+23.7/−10.4)% in LRDs and 2.2(+1.7/−1.0)% in UV-selected galaxies at z>4, implying hard radiation fields in a small subset and that dense H I may not fully cover some LRD nuclei. The line ratios and non-detections argue for extending searches down to the NV doublet, though statistics remain limited by the number of deep rest-UV spectra.

LRD spectroscopy high-z broad Balmer demographics

2025-05-09 · 2505.06198v1

The "Dark-Matter Dominated" Galaxy Segue 1 Modeled with a Black Hole and no Dark Halo

Nathaniel Lujan, Karl Gebhardt, Richard Anantua, et al.

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Orbit-based dynamical models of Segue 1 favor a central intermediate-mass black hole of 4 ± 1.5 × 10^5 M⊙, reproducing the stellar kinematics with a near-isotropic orbital structure. Zero–black-hole models both fit worse and require an extremely compact dark halo (scale radius ~100 pc) plus highly radial stellar orbits, while the BH model is also supported by a central rotation spike of 9.0 ± 2.4 km s−1. The tracer profile is built from number counts with tidal-stream subtraction and deprojection, and the stellar mass-to-light ratio remains poorly constrained, underscoring non-stellar mass dominance. Taken together, Segue 1 looks like a tidally stripped nuclear remnant and a nearby analog of Little Red Dots with overmassive black holes.

overmassive BH low-z

2025-05-09 · 2505.05942v1

Green Flash: Residual Emissions Enshrouded in Low-mass Balmer-break Galaxies at $z\sim5$

Kosuke Takahashi, Takahiro Morishita, Tadayuki Kodama, et al.

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JWST/NIRCam+NIRSpec data are used to isolate four low-mass Balmer-break galaxies in Abell 2744 at z=5.10–5.78 and fit their SEDs, showing they have been largely quiescent for ~100 Myr despite residual strong lines. All four require higher nebular than continuum attenuation, pointing to dusty star-forming pockets or obscured AGN as a lingering signature of quenching. For one galaxy with medium-band leverage, an Hβ+[O III] map shows centrally concentrated emission (Re≈0.7 kpc) that is more compact than the stellar body (Re≈0.9 kpc), favoring an outside-in quenching picture. Notably, one object (ID52153) sits on the z~5 main sequence even with a Balmer break, underscoring obscuration/bursty residual activity.

high-z spectroscopy

2025-05-08 · 2505.05556v1

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

Giada Quadri, Alessandro Trinca, Alessandro Lupi, et al.

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Zoom-in cosmological simulations of a quasar host including super-Eddington accretion track how MBH feedback shapes gas, star formation, and emergent spectra. Outflows usually vent perpendicular to the disc and only moderately suppress the SFR, but after rapid super-Eddington growth the galaxy spends ≈10% of its lifetime in a distinct quenched state. This phase culminates in a powerful jet+disc-wind event that couples to the disc and excavates a central cavity. Across its history the system’s spectra can look like little red dots or quenched galaxies, implying both are transient stages in early quasar hosts.

simulation super-Eddington outflows LRD high-z QSO

2025-05-07 · 2505.04826v1

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) XXII. Chandra observations of narrow-line quasar candidates at z>6

K. Iwasawa, R. Gilli, F. Vito, et al.

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Chandra followed up four z>6 SHELLQs narrow-line quasar candidates chosen for luminous Lyα and faint UV continua, and found no X-ray detections, placing L2–10 keV < 2×10^44 erg/s (2σ; Γ=2). JWST/NIRSpec reveals weak broad Balmer bases beneath narrow cores, while strong [O III] would predict Lx ≈ 10^45 erg/s from low‑z scaling, in stark tension with the Chandra limits. The authors argue for heavily buried nuclei—either Compton-thick columns in dense ISM or an inclined, inflated inner disc in supercritical accretion—making these sources higher-luminosity analogs of JWST-selected broad-line AGN at reionization. The work clarifies how extreme Lyα–bright, UV-faint quasars can hide powerful engines early on.

obscured AGN X-ray luminous quasar high-z spectroscopy

2025-05-07 · 2505.04825v1

SHELLQs. Bridging the Gap: JWST Unveils Obscured Quasars in the Most Luminous Galaxies at z > 6

Yoshiki Matsuoka, Masafusa Onoue, Kazushi Iwasawa, et al.

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From the SHELLQs wide-field UV survey, the team followed 13 z>6, Lyα-luminous galaxies with JWST/NIRSpec and uncovered obscured quasars. Seven of eleven narrow‑Lyα systems show broad H I Balmer and He I components—but not in [O III]—with Balmer decrements indicating mild obscuration (0<Av<3), identifying them as UV‑obscured counterparts of luminous EoR quasars. Virial lines imply MBH≈10^(7.8–9.1) Msun with sub‑Eddington to Eddington accretion; most BL sources are unresolved and display LRD‑like blue‑UV/red‑optical colors. The AGN incidence among similarly bright Lyα emitters (≥2×10^−8 Mpc^−3) is comparable to classical quasar densities, implying a substantial obscured SMBH population previously missed by UV‑bright surveys.

obscured AGN luminous quasar high-z broad Balmer spectroscopy JWST AGN

2025-05-07 · 2505.04609v1

CAPERS-LRD-z9: A Gas Enshrouded Little Red Dot Hosting a Broad-line AGN at z=9.288

Anthony J. Taylor, Vasily Kokorev, Dale D. Kocevski, et al.

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CAPERS-LRD-z9 is a PRIMER-selected little red dot spectroscopically confirmed with NIRSpec/PRISM as a z=9.288 broad-line AGN via a ~3500 km s−1 Hβ plus narrow [O III] λλ4959,5007. The broad Hβ implies a canonical black-hole mass log(MBH/M⊙)=7.58±0.15 (allowing 6.65–8.50 with systematics). A pronounced Balmer break requires a dense (~10^10 cm−3) neutral-gas cocoon around the nucleus; SED modeling (CLOUDY+bagpipes) limits the host to M*<10^9 M⊙, hinting at MBH/M* possibly >5% and a UV continuum that may be AGN-dominated. Together, these properties push early BH growth scenarios toward massive seeds or super‑Eddington episodes within ≲500 Myr of cosmic time.

LRD broad-line AGN high-z broad Balmer spectroscopy BH seeds

2025-05-06 · 2505.03183v1

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

Chang-Hao Chen, Luis C. Ho, Ruancun Li, et al.

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This Letter decomposes NIRCam imaging in 8 broad and 9 medium bands to isolate off-centered emission around four LRDs in Abell 2744 (UNCOVER + MegaScience). Three blobs are confirmed to be physically associated with their LRDs, with two showing medium-band excess consistent with very strong [O III] λλ4959,5007. While all three SEDs can be fit as ~10^8 Msun star-forming systems, the two [O III]-extreme cases are best explained as pure nebular emission from low-density, low-metallicity gas photoionized by the nearby LRD. Adopting LRD halo masses, the implied baryonic halo accretion rates are ~2–9 Msun/yr, suggesting growth to ~10^9 Msun by z≈4 if sustained at 10% star-formation efficiency.

LRD nebular continuum

2025-05-05 · 2505.02908v1

Early Shock-Cooling Observations and Progenitor Constraints of Type IIb SN 2024uwq

Bhagya M. Subrayan, David J. Sand, K. Azalee Bostroem, et al.

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Early multiwavelength follow-up of the Type IIb SN 2024uwq captures the shock-cooling bump and the subsequent second peak, with early spectra showing broad H-alpha (~15,500 km s^-1) and He I P-Cygni features of comparable strength that evolve toward stronger He and fading H. Modeling of the shock-cooling phase and a bolometric light-curve fit (two-component Arnett) favor a partially stripped progenitor with radius 10–60 R_sun and a residual hydrogen envelope of 0.7–1.35 M_sun. The inferred ZAMS mass of 12–20 M_sun and likely binary stripping place SN 2024uwq between compact and extended IIb events. The work underscores the value of very-early UV/optical coverage for mapping the continuum of stripped-envelope progenitors.

broad Balmer spectroscopy stellar envelope

2025-05-05 · 2505.02895v1

Abundant Population of Broad H$α$ Emitters in the GOODS-N Field Revealed by CONGRESS, FRESCO, and JADES

Junyu Zhang, Eiichi Egami, Fengwu Sun, et al.

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Using JWST/NIRCam WFSS from FRESCO and CONGRESS plus JADES imaging, the authors conduct a GOODS‑N search for broad Hα at z≈3.7–6.5 and confirm 19 emitters at z≈4–5.5, including nine new ones. Their broad Hα LF aligns with other JWST BLAGN results, and virial BH masses with bolometric corrections imply ≈0.1 Eddington accretion and elevated MBH/M* relative to local relations. Color comparisons show LRD cuts miss 42% of these spectroscopic AGN—many lack the steep rest‑optical red slope—and average SEDs indicate some LRD red slopes are line‑boosted. Notably, 68% of color‑selected LRDs with Hα detections lack broad lines in the grism data, potentially due to sensitivity limits, underscoring the LRD population’s mixed nature.

broad-line AGN broad Balmer spectroscopy demographics LRD high-z

2025-05-02 · 2505.01499v1

An extremely metal-poor Lyman $α$ emitter candidate at $z=6$ revealed through absorption spectroscopy

Dominika Ďurovčíková, Anna-Christina Eilers, Robert A. Simcoe, et al.

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Archival VLT/MUSE data reveal a Lyα emitter at z=6.0323 just 29 pkpc in front of the quasar PSO J158-14 (z=6.0685), previously missed because it leaves no metal absorption in the quasar spectrum. The Lyα line sits at the edge of the quasar proximity zone, and a proximate sub-DLA with log N_HI≈19.7 reproduces the observed damping wing. Deep (>10 hr) FIRE+X-shooter spectroscopy yields [Z/H] < −3 after ionization-correction modeling, marking this source as an extremely metal-poor galaxy candidate. This system offers a rare window on near-pristine gas and potential Population III signatures during reionization.

high-z reionization spectroscopy

2025-04-28 · 2504.20299v1

The Cosmic Evolution of CIV Absorbers at $1.4<z<4.5$: Insights from $100,000$ Systems in DESI Quasars

Abhijeet Anand, J. Aguilar, S. Ahlen, et al.

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From 300,637 DESI quasar spectra, the team assembles the largest C IV absorber catalog to date—101,487 systems across 1.4<z<4.5—via an automated matched‑kernel finder with adaptive S/N thresholds. After Monte Carlo completeness corrections (50% complete at EW_CIV ≥ 0.4 Å), the EW frequency distribution declines exponentially with weak redshift evolution, while the incidence per comoving path rises by a factor of 2–5 toward z≈1.4, most strongly for the strongest systems. Apparent‑optical‑depth column densities yield Ω_CIV increasing by ~3.8×, from (0.82±0.05)×10^-8 at z≈4.5 to (3.16±0.2)×10^-8 at z≈1.4. Interpreting Ω_CIV as enrichment, they infer a lower limit log(Z_IGM/Z⊙) ≳ −3.25 at z≈2.3, tracking cosmic SFR and He II photoheating and providing a foundation to link CGM metals to galaxy growth near cosmic noon.

demographics QSO spectroscopy

2025-04-25 · 2504.18616v1

Insights on Metal Enrichment and Environmental Effect at $z\approx5-7$ with JWST ASPIRE/EIGER and Chemical Evolution Model

Zihao Li, Koki Kakiichi, Lise Christensen, et al.

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Using JWST/NIRCam WFSS across 26 quasar fields (ASPIRE+EIGER), the authors build a [O III]-selected sample of 604 galaxies at z=5.34–6.94 and flag 204 protocluster members via a friends-of-friends search. Stacked spectra detect Hγ and [O III] λ4363, giving Te=2.0(+0.3,-0.4)×10^4 K and a metal-poor median 12+log(O/H)=7.65(+0.26,-0.15). With NIRSpec-anchored strong-line calibrations, the MZR shows ≈0.2 dex higher metallicity at the high-mass end in overdense regions, while the full z>5 sample sits ≈0.2 dex below the local FMR. A simple chemical-evolution model points to dilution from intense gas accretion, with protocluster galaxies closer to gas equilibrium—evidence for accelerated early enrichment during protocluster assembly at z≈5–7.

high-z spectroscopy

2025-04-23 · 2504.17007v1

The First Photometric Evidence of a Transient/Variable Source at z>5 with JWST

Christa DeCoursey, Eiichi Egami, Fengwu Sun, et al.

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Reports AT 2023adya, a transient/variable source in a z_spec=5.274 GOODS-N galaxy, detected via a 0.19 mag fade in F356W over ~2 rest-frame months with a significant difference-image residual (SN_var≈6). No contemporaneous variability is seen in the rest-UV (F090W/F115W), and the rest-frame V-band absolute magnitude is MV≈−18.48. NIRCam/Grism data show no broad Hα (FWHM=130±26 km s−1), disfavoring an AGN origin; Ia is possible but unlikely given low high‑z rates, with CCSN remaining plausible while TDEs are disfavored by low event rates. The result establishes practical JWST sensitivity to transient/variable phenomena beyond z>5, nudging discovery space toward the reionization era.

variability high-z spectroscopy

2025-04-22 · 2504.15913v1

A Massive Gas Outflow Outside the Line-of-Sight: Imaging Polarimetry of the Blue Excess Hot Dust Obscured Galaxy W0204-0506

Roberto J. Assef, Marko Stalevski, Lee Armus, et al.

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VLT/FORS2 imaging polarimetry of the blue-excess Hot DOG WISE J020446.13–050640.8 (W0204–0506) finds a spatially integrated UV polarization of 24.7 ± 0.7% in R_Special, clinching a scattered-light origin for the faint blue continuum. The source is resolved, showing a polarization fraction and angle gradient aligned with the HST/WFC3 morphology, which SKIRT radiative-transfer models reproduce with a dusty conical polar outflow that starts at the sublimation radius, has half-opening angle ≤50°, and is viewed at inclination ≥45°, favoring graphite-rich dust. Inferred gas mass and outflow velocity fall within ranges seen for [O III] outflows in other Hot DOGs, though the feedback impact on the host remains uncertain. The work showcases imaging polarimetry as a geometry probe for dusty quasar outflows complementary to spectroscopy.

obscured AGN outflows luminous quasar

2025-04-18 · 2504.13658v1

SRGAJ230631.0+155633: an extremely X-ray luminous, heavily obscured, radio-loud quasar at z=0.44 discovered by SRG/ART-XC

Grigory Uskov, Sergey Sazonov, Igor Lapshov, et al.

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SRGA J230631.0+155633 is a z=0.4389, type 2, radio‑loud quasar uncovered by SRG/ART‑XC (4–12 keV) and followed up near‑simultaneously with ART‑XC and Swift/XRT in June 2023, revealing heavy absorption with N_H ≈ 2×10^23 cm^-2. Its intrinsic 2–10 keV luminosity declined from (6^{+6}_{−3})×10^45 erg s^-1 during the 2020–2021 all‑sky scans to (1.0^{+0.8}_{−0.3})×10^45 erg s^-1 in 2023, indicating strong rest‑frame ~1 yr variability while remaining quasar‑luminous. Radio imaging shows a core plus two extended lobes consistent with a giant FR II radio galaxy. Multi‑wavelength constraints imply L_bol ~6×10^46 erg s^-1 and M_BH ~1.4×10^9 M_⊙ (λ_Edd ~0.3), making this one of the most luminous obscured quasars out to z ≈ 0.5 and a nearby laboratory for buried SMBH growth.

obscured AGN luminous quasar X-ray radio variability low-z

2025-04-15 · 2504.11566v1

Tracking the assembly of supermassive black holes: a comparison of diverse models across cosmic time

Antonio J. Porras-Valverde, Angelo Ricarte, Priyamvada Natarajan, et al.

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The authors cross-compare SMBH assembly across semi-analytic, empirical, and hydro frameworks (Dark Sage, Santa Cruz SAM, RN18, TRINITY, TNG300) over MBH ≈ 10^6–10^10 Msun. Physics-based models diverge from observationally inferred local BHMFs due to stellar-mass-function and scaling-relation systematics, but converge at z ~ 1–4 and broadly match JWST broad-line AGN BHMFs at z = 4–5. Dark Sage uniquely produces a strong knee in the bolometric AGN luminosity function near Lbol ~ 10^46 erg s^-1 that overlaps the inferred luminosities of JWST “Little Red Dots” at z = 5–6 if the emission is AGN-dominated. Within Dark Sage, SMBHs grow mainly via secular disk instabilities and merger-driven cold gas accretion, while BH–BH mergers contribute ~60% of the mass only for the most massive systems by z = 0; super-Eddington accretion is allowed.

simulation demographics high-z super-Eddington

2025-04-15 · 2504.11531v1

Oxyster: A Circumgalactic Low-ionization Oxygen Nebula next to a Starburst Galaxy at $z\sim1$

Pengjun Lu, Mingyu Li, Dalya Baron, et al.

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Subaru/HSC narrow-band NB718/NB973 imaging plus Magellan LDSS3 follow-up reveal “Oxyster,” a CGM oxygen nebula next to a disturbed, interacting starburst at z=0.924, extending ~30 kpc in [O II] and ~20 kpc in [O III]. On the luminosity–size plane it outscales low‑z ENLRs and evokes a high‑z Voorwerp analog, but shows uniformly low O32 and no Hβ. HST/JWST imaging and SED fitting place the 2–6×10^10 Msun host above the main sequence with <5% AGN contribution and no X-ray/radio AGN, while standard photoionization/shock models cannot reproduce the luminosities, low O32, and Hβ non‑detection. The authors favor a recent (<10^8 yr) starburst plus a low‑luminosity AGN (~10^42 erg s^-1), underscoring narrow-band searches as a route to CGM mapping around non‑AGN systems near z~1.

spectroscopy low-z

2025-04-14 · 2504.10731v1

Unveiling faint X-ray AGN populations in the NewAthena era: Insights from cosmological simulations

Nuno Covas, Israel Matute, Stergios Amarantidis, et al.

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From a TNG300-based 10 deg^2 SMBH light cone with post-processed X-ray properties, the authors run end-to-end NewAthena/WFI simulations via SIXTE to stress-test faint and high‑z AGN performance. The mock predicts a 5× excess of faint AGN versus current X‑ray constraints, plausibly reconciled by a higher Compton‑thick fraction and intrinsic X‑ray weakness hinted by recent JWST work. The simulated survey yields ~250,000 AGN (≈20,000 at z>3) and ~35 at z>6, with only log L_X ≳ 43.5 detectable in the EoR and a significant CTK component out to z>4. These results argue NewAthena can directly probe early SMBH growth while informing instrument trades and survey tiling.

X-ray simulation high-z obscured AGN demographics

2025-04-14 · 2504.10596v1

An obscured quasar census with the 4MOST IR AGN survey: design, predicted properties, and scientific goals

Carolina Andonie, David M. Alexander, Claire Greenwell, et al.

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Introduces the 4MOST IR AGN survey, a ~10,000 deg^2, rAB≤22.8 program targeting ≈212k mid-IR–selected obscured AGN via unWISE colors plus an r−W2≥5.9 mag cut. Using X-ray spectral constraints and UV–far-IR SEDs in four deep fields, they forecast 80–87% AGN purity with ≈70% obscured (NH>10^22 cm−2) and that ≈80% of targets will evade even the deepest eROSITA exposures. About 55% will be quasar-luminous (LAGN,IR>10^45 erg s−1) at z≈0.5–3.5 in massive (10^10–10^12 M⊙) hosts, with ≈33% in starbursts. This 100× expansion over prior spectroscopic obscured-IR samples will deliver a uniform census of heavily absorbed, X-ray–faint quasars complementing the 4MOST X-ray AGN survey.

obscured AGN demographics spectroscopy luminous quasar

2025-04-14 · 2504.10581v1

Massive Black Hole Seed Formation in Strong X-ray Environments at High Redshift

Kazutaka Kimura, Kohei Inayoshi, Kazuyuki Omukai

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Semi-analytic merger-tree modeling with observationally calibrated X-ray irradiation (guided by HERA’s 21 cm non-detections) shows that strong X-ray backgrounds boost H2 formation, steering most overdense halos off the classic direct-collapse path. Including baryonic streaming motion preserves an atomic-cooling route in a subset of cases, still yielding massive seeds. The model predicts seeds with M_BH ≳ 10^4 Msun by z ≃ 15 and an abundance ≈10^-4 Mpc^-3, sufficient to account for SMBHs verified by JWST spectroscopy at 3<z<6. X-ray ionization prevents formation of extremely overmassive BHs comparable to their hosts, while establishing BH-to-stellar mass ratios ≃0.01–0.1 at seeding.

BH seeds simulation high-z reionization X-ray

2025-04-14 · 2504.10573v1

High-$z$ radio Quasars in RACS I: Selection, identification, and multi-wavelength properties

L. Ighina, A. Caccianiga, A. Moretti, et al.

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Cross-matching RACS-low (888 MHz) with DES and Pan-STARRS, the authors selected 45 bright radio/optical-dropout candidates (S_888MHz>1 mJy, z_mag<21.3) over 16,000 deg^2 and spectroscopically confirmed 24 new quasars, 13 at 4.5<z<5 and 11 at z>5. Including comparable literature objects, the z>5 RACS set reaches 33 powerful radio quasars with νL_1.4GHz≈10^41.5–10^44.4 erg s^-1 and is ~90% complete at the stated flux and magnitude limits. Multi-band radio plus new X-ray coverage (Chandra, uGMRT, MeerKAT, ATCA) reveal predominantly flat spectra (22 with −0.5<α_r<0.5) and X-ray luminosities exceeding coronal expectations. The combined evidence points to many blazar-like, jet-aligned systems, delivering a bright, homogeneous anchor sample for population studies of early SMBH growth.

QSO radio high-z spectroscopy X-ray luminous quasar

2025-04-10 · 2504.08067v1

Disk-jet coupling across the spectral transition in supermassive black holes

Jia-Lai Kang, Chris Done, Scott Hagen, et al.

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Stacks of VLASS images for eROSITA-selected, unobscured AGN in a single mass bin (log M/M☉=8–8.5) track radio behavior across the spectral transition identified from optical/UV–X-ray SEDs. After subtracting matched host-galaxy star-formation radio, the residual core radio stays roughly constant through the transition while the mean accretion rate rises by ~6× and the UV disk brightens by ~100×; the X-rays change by only ~2×, yielding an approximately constant radio/X-ray ratio consistent with the Fundamental Plane. The result favors a persistent, compact jet coupled to the X-ray hot flow (not the thin disk), explaining why radio-loudness flips mainly reflect optical/UV changes rather than jet quenching. Compared to binaries, AGN retain strong coronal X-rays in the disk-dominated state, accounting for the continued radio–X coupling.

2025-04-10 · 2504.08039v1

Bridging Quasars and Little Red Dots: Insights into Broad-Line AGNs at $z=5-8$ from the First JWST COSMOS-3D Dataset

Xiaojing Lin, Xiaohui Fan, Feige Wang, et al.

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From the first 10% (≈127 arcmin²) of COSMOS-3D NIRCam grism WFSS, the team identifies 13 broad-line AGNs at z=5–8 via Hα/Hβ, including a z=7.646 Hβ source at F444W=23.6, among the brightest z>7.5 BL AGN. Most (10/13) show reddened optical continua with β_opt>0, while three have quasar-like SEDs that are less blue than unobscured QSOs; two objects have 7.7–18 μm MIRI points constraining rest-NIR, and no significant F115W UV variability is seen over Δt_rest≈60 days. The Hα luminosity functions at z≈5–6 hint at evolution relative to z≈4–5. An Hβ LF at z∼8 implies number densities ~100× above UV-selected quasar LFs, pointing to a populous bridge between UV-bright quasars and LRD-like BL AGN.

JWST AGN broad-line AGN high-z spectroscopy demographics broad Balmer

2025-04-10 · 2504.08032v1

Counting Little Red Dots at $z<4$ with Ground-based Surveys and Spectroscopic Follow-up

Yilun Ma, Jenny E. Greene, David J. Setton, et al.

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Using ~3.1 deg^2 of ultra-deep HSC plus (near-)IR imaging, the authors assemble a ground-based sample of Little Red Dots at 2≲z≲4 and measure their abundance for M5500<-22.5. They find a sharp decline in number density from ~10^-4.5 cMpc^-3 at z>4 to ~10^-5.3 at 2.7<z<3.7 and ~10^-5.7 at 1.7<z<2.7, extending LRD demographics below z~4. A Magellan/FIRE spectrum of DEEP23-z2LRD1 (z_spec=2.26) shows broad Hα (FWHM≈2400 km s^-1) plus nearly symmetric narrow Hα absorption and extremely narrow [OIII] (FWHM≈140 km s^-1), consistent with an accreting BH in a low-mass host. Because ground-based resolution limits can admit contaminants, the paper stresses that spectroscopy is required to firm up the z<4 LRD number densities.

LRD demographics spectroscopy broad Balmer low-z

2025-04-09 · 2504.07196v1

Joint Survey Processing. III. Compact Oddballs in the COSMOS Field -- Little Red Dots and Transients

Yu-Heng Lin, Andreas L. Faisst, Ranga-Ram Chary, et al.

HST/ACS G800L grism follow-up of seven compact, 8000 Å–dropout COSMOS point sources tests the faint z≈6 AGN candidate pool. Only one object (772319) is detected in multiple bands with a V-shaped, LRD-like SED and is ~3 mag brighter than typical JWST LRDs; no Lyα or other common lines appear in the grism. From the non-detections they place an upper limit on the AGN UV luminosity function of Φ=1.1×10^-7 Mpc^-3 mag^-1 at M_UV=−21. The remaining sources show F814W vs Subaru i+z flux mismatches not attributable to emission lines, implying long-lived transients with observed-frame decay timescales ≤6 years and highlighting transient contamination of faint-AGN searches.

LRD v-shaped SED high-z spectroscopy demographics

2025-04-04 · 2504.03848v1

Large-scale surveys of the quasar proximity effect

Rupert A. C. Croft, Patrick Shaw, Ann-Marsha Alexis, et al.

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Develops a CDM halo-model framework for the quasar proximity effect that explicitly includes overdense quasar environments and fits individual Lyα spectra for the radiation-equality radius r_eq and large-scale quasar bias b_q, validated on the ASTRID hydrodynamic simulation. Demonstrates that r_eq can be recovered without bias from a single spectrum with 25–50% statistical uncertainty. Scaling to DESI-sized samples enables precise measurements of the UV background intensity and its redshift evolution. Using the Uchuu simulation, shows that proximity-effect measurements could map spatial UV radiation fluctuations and measure their power spectrum on 100–1000 h−1 Mpc scales, making the radiation field a cosmological observable alongside density.

QSO reionization simulation high-z spectroscopy

2025-04-04 · 2504.03551v1

JADES: comprehensive census of broad-line AGN from Reionization to Cosmic Noon revealed by JWST

Ignas Juodžbalis, Roberto Maiolino, William M. Baker, et al.

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Using JADES spectroscopy, the authors assemble a uniform census of 34 broad-line (Type 1) AGN spanning 1.5<z<9 with virial black-hole masses of 10^6–10^9 M⊙ and bolometric luminosities down to 10^43 erg s^-1, generally at sub-Eddington rates (<0.5 L_Edd). These AGN are typically in low-mass (M⋆≈10^8 M⊙) hosts whose black holes are overmassive relative to the local M_BH–M⋆ relation yet consistent with the local M_BH–σ⋆ relation, enabling a view of how these scalings emerge across cosmic time. The team shows that standard narrow-line diagnostics would miss many counterparts—especially at low metallicity or with attenuated/soft ionizing continua—complicating Type 2 selection. They also find strong cosmic-variance sensitivity in the UV luminosity function and rule out electron/Balmer scattering as the origin of broad Balmer components, arguing BH masses are not severely overestimated.

broad-line AGN JWST AGN broad Balmer demographics overmassive BH high-z

2025-04-04 · 2504.03422v1

XXL-HSC: Host properties of X-ray detected AGNs in XXL clusters

E. Drigga, E. Koulouridis, E. Pouliasis, et al.

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Using 82 X-ray AGN within 4 r500 of 164 XXL clusters (z ≲ 1) and deep HSC imaging, the authors classify host morphologies (Statmorph + visual) and assess obscuration and SFR via X-ray hardness ratios, optical spectra, and SEDs. They find a moderately significant excess of cluster AGN hosted by merging/disturbed galaxies relative to non-active cluster members and field AGN, with the signal concentrated in the outskirts (≈1–2 r500). Clusters also show a higher share of X-ray-hard (likely obscured) AGN than the field, especially in the outskirts. Together, the results point to mergers/interactions in cluster outskirts as key drivers of both AGN triggering and obscuration.

X-ray obscured AGN demographics low-z

2025-04-03 · 2504.02683v1

Probing patchy reionisation with JWST: IGM opacity constraints from the Lyman-$α$ forest of galaxies in legacy extragalactic fields

Romain A. Meyer, Guido Roberts-Borsani, Pascal Oesch, et al.

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Using public JWST/NIRSpec PRISM spectra of z≈4–7 galaxies, the authors detect the Gunn–Peterson trough in stacked galaxy spectra and derive the first galaxy-based IGM Lyα opacity measurements, plus intrinsic Lyβ opacity at 5<z<6. The galaxy-based opacities agree with state-of-the-art quasar Lyman-α forest constraints and will sharpen as JWST samples grow. In GOODS-South, a z=5.8–5.9 overdensity of galaxies and Lyα emitters coincides with an anomalously low Lyα IGM opacity, directly linking local large-scale structure to an over-ionised IGM patch. The required photo-ionisation rate can be produced by galaxies down to M_UV≲−10 if log10⟨ξion fesc⟩≈25 (e.g., log10 ξion=25.4 with fesc=0.4).

reionization spectroscopy high-z

2025-04-02 · 2504.01852v1

Deciphering the Nature of Virgil: An Obscured AGN Lurking Within an Apparently Normal Lyman-α Emitter During Cosmic Reionization

Pierluigi Rinaldi, Pablo G. Pérez-González, George H. Rieke, et al.

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JWST/MIRI imaging plus deep NIRSpec/PRISM place the LAE “Virgil” at z=6.6379 and reveal Little Red Dot–like photometry with an extreme color F444W−F1500W=2.84±0.04, and a strongly rising mid-IR SED. SED fits across multiple codes favor an obscured AGN whose IR slope and UV excess resemble blue-excess HotDOGs. The host shows subsolar metallicity, low–moderate dust, and high ionization/electron temperature; UV and Hα SFRs suggest Virgil is entering or fading a burst. High‑z line‑ratio diagnostics (e.g., O32–R23, Ne3O2) nominally flag AGN, though this is ambiguous after accounting for redshift evolution; a tentative broad Hα improves residuals only marginally, while the new 15 μm data strengthen the AGN case and highlight MIRI’s leverage on early black‑hole growth.

LRD obscured AGN JWST AGN high-z spectroscopy reionization