654 indexed papers · 430 research notes

Research archive

2025-08-12 · 2508.08768v1

Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots

Seok-Jun Chang, Max Gronke, Jorryt Matthee, et al.

The authors run 3D Monte Carlo radiative transfer to test how resonance, Raman, and Thomson scattering sculpt Balmer lines in Little Red Dots. Resonance scattering in an n=2–populated H I medium drives strong departures from Case B and distinct Hα vs Hβ shapes, but Hβ is funneled into Paα, preventing broad Hβ wings. Raman scattering of higher Lyman-series emission can explain Hα/Hβ wing-width ratios ≳1.28, whereas Ramanization of a UV continuum is disfavored by the near-constant FWHM across transitions. Thomson scattering with Te≈10^4 K and electron column ≈10^24 cm−2 reproduces the ≳1000 km s−1 wings and implies virial BH masses can be overestimated by ≳10 if widths are taken at face value.

LRD broad Balmer simulation overmassive BH spectroscopy

2025-08-04 · 2508.02792v1

Luminous Mid-IR Selected Obscured Quasars at Cosmic Noon in SDSS Stripe82 II: Spectroscopic Diversity and Broad H$α$ Emissions

Ben Wang, Yuzo Ishikawa, Joseph F. Hennawi, et al.

Download highlighted PDF arXiv abstract

Survey of 24 WISE W4–bright, optically faint/red SDSS Stripe 82 candidates confirms 23 luminous Type‑2 quasars at z = 0.88–3.49 using Gemini/GNIRS plus Keck/LRIS and KCWI spectra. About one‑third (8/23) unexpectedly show broad Hα (FWHM > 2000 km/s) while sharing SEDs with JWST “little red dots,” marking them as lower‑z analogues of heavily obscured broad‑line AGN. The sample also exhibits relatively weak [O III] λ5007 given their high bolometric luminosities, and the authors construct a new Type‑2 QSO composite spectrum. Results demonstrate that simple mid‑IR plus extreme r−W4 color selection efficiently recovers a spectroscopically diverse obscured quasar population at cosmic noon, informing SMBH growth demographics that connect to the LRD population.

QSO obscured AGN broad Balmer spectroscopy low-z demographics

2025-08-02 · 2508.01372v1

A Nitrogen-rich AGN Powering a Large Ionizing Bubble at z=8.63

Takahiro Morishita, Massimo Stiavelli, Charlotte A. Mason, et al.

arXiv abstract

New NIRSpec/MSA G140H/F070LP data reveal broad Lyα in CANUCS-LRD-z8.6 (z=8.63) centered near systemic (FWHM 1540±260 km/s), implying transmission through a large reionized region. Simple Strömgren modeling of the line shape yields an ionized-bubble radius Rb=1.5^{+0.3}_{-0.2} pMpc and a Lyα escape fraction fesc=11±3%. The intrinsic width is even broader (≈2200±280 km/s), consistent with a BLR in a low-luminosity AGN, while high N IV]/C IV and N IV]/O III] ratios from PRISM indicate nitrogen enrichment. A mild local overdensity (δ≈1.8) suggests neighboring galaxies may help sustain the bubble, linking this LRD to the emerging class of nitrogen-rich systems like GN-z11 and GHZ2/GLASSz12.

LRD broad-line AGN reionization spectroscopy high-z

2025-07-30 · 2507.23066v1

SHELLQs-JWST perspective on the intrinsic mass relation between supermassive black holes and their host galaxies at z > 6

John Silverman, Junyao Li, Xuheng Ding, et al.

Download highlighted PDF arXiv abstract

Using nine SHELLQs quasars at 6.18<z<6.4 with NIRCam host detections and NIRSpec Balmer-line M_BH, the authors infer the intrinsic M_BH–M_* relation via forward modeling that accounts for selection and measurement systematics, with the slope fixed to 1.61 and acknowledging parameter degeneracies. The sample (log M_BH≈8–9; log M_*≈9.5–11) is consistent with a non-evolving relation but with markedly larger intrinsic scatter, σ≈0.80 dex. The preferred model implies an active UV-unobscured AGN fraction of ~2.3% at z≈6 and predicts many lower-mass AGN soon to be found. An overmassive normalization is disfavored, as it would require unrealistically small scatter (~0.22 dex) and a very low AGN fraction (~0.6%).

QSO high-z spectroscopy demographics JWST AGN

2025-07-28 · 2507.20684v1

A deep dive down the broad-line region: permitted OI, CaII and FeII emission in an AGN Little Red Dot at z=5.3

Roberta Tripodi, Maruša Bradač, Francesco D'Eugenio, et al.

Download highlighted PDF arXiv abstract

JWST/NIRCam imaging and NIRSpec prism spectroscopy of the Bullet‑cluster LRD Bz5.3 (zspec=5.2907) reveal broad Balmer emission plus strong low‑ionization Fe II, O I, and Ca II triplet lines, confirming a bona fide BLR around an accreting SMBH. The work reports the first high‑z detection of the O I λ1304 bump (O I+Si II), alongside prominent O I λ8446 and Ca II λλ8498,8542,8662. A markedly low O I λ1304/λ8446 photon ratio (0.1–0.3) implies internal dust with AV≈0.4–1.0 and points to Lyβ fluorescence as the dominant excitation, consistent with high EW O I λ8446 and weak O I λ7774. Photoionization modeling of O I and Ca II favors multiple BLR gas phases with distinct densities/ionization states, supporting a stratified BLR at early times.

LRD broad-line AGN broad Balmer spectroscopy high-z

2025-07-14 · 2507.10674v1

BASS. XLIX. Characterization of highly luminous and obscured AGNs: local X-ray and [NeV]$λ$3426 emission in comparison with the high-redshift Universe

Alessandro Peca, Michael J. Koss, Kyuseok Oh, et al.

Download highlighted PDF arXiv abstract

A BAT-selected local analog set of 21 highly luminous, obscured Seyfert 1.9–2 AGN at z<0.6 (log L_X,2–10keV>44.6) is modeled with NuSTAR, XMM-Newton, Suzaku, and Chandra to recover N_H, Γ, intrinsic L_X, covering factor, Fe Kα, and [NeV] λ3426. The sample is highly variable: 82% vary overall (73% in 2–10 keV flux; 33% in line-of-sight N_H), and 6/12 with M_BH estimates fall in the N_H–λ_Edd “forbidden region,” where they also show enhanced N_H variability/outflow signatures—consistent with a clearing phase. [NeV] λ3426 is detected in 85% and, when renormalized to the same [OIII] peak, is significantly stronger than in JWST-selected z=2–9 narrow-line AGN. These local benchmarks calibrate [NeV]-based obscured AGN searches and frame expectations for future high‑z X-ray follow-up.

obscured AGN X-ray low-z variability outflows spectroscopy

2025-07-11 · 2507.08929v1

Ruling out dominant electron scattering in Little Red Dots' Rosetta Stone using multiple hydrogen lines

Matilde Brazzini, Francesco D'Eugenio, Roberto Maiolino, et al.

Download highlighted PDF arXiv abstract

Targets the LRD “Rosetta Stone” GN-28074 (z=2.26) and tests whether broad Balmer/Paβ wings are dominated by wavelength-independent electron scattering. Using JWST/NIRSpec MSA medium-resolution data (∼1.7 hr), the authors compare Hα, Hβ, and Paβ profiles in velocity space and find mismatched wing shapes, contrary to the electron-scattering prediction of identical profiles. Joint fits with Gaussian BLR components plus exponential scattering wings cannot simultaneously match all three lines with physically plausible parameters. Result: dominant electron scattering around the BLR is ruled out for GN-28074, arguing against a universal systematic BH-mass overestimation in LRDs.

LRD broad Balmer spectroscopy

2025-07-11 · 2507.08298v1

Obscured and unobscured X-ray AGNs I: Host galaxy properties

Carlos G. Bornancini, Gabriel A. Oio, Georgina Coldwell

Download highlighted PDF arXiv abstract

X-ray selected AGNs from zCOSMOS (0.5<z<0.9) are split by obscuration (NH) and excitation (log[OIII]/Hβ>0.5) to compare host properties. Unobscured sources show a clearer rise of the ionization index O32=[OIII]/[OII] with L2–10 keV than obscured ones, while high-excitation obscured AGNs reach higher X-ray luminosities on average. High-excitation systems also have elevated R23, implying lower gas metallicities reminiscent of z~4–6 galaxies. λsBHAR positively correlates with NH, O32, and R23, linking high specific accretion to harder radiation fields in less enriched environments.

obscured AGN X-ray spectroscopy demographics low-z

2025-07-09 · 2507.07160v1

Empirical Calibration of Na I D and Other Absorption Lines as Tracers of High-Redshift Neutral Outflows

Lorenzo Moretti, Sirio Belli, Gwen C. Rudie, et al.

Download highlighted PDF arXiv abstract

A cleverly aligned system lets the authors directly calibrate neutral outflow tracers: a massive quiescent galaxy J1439B at z=2.4189 sits 38 kpc from the sightline to QSO J1439+1117, where its outflow appears as a sub-DLA enabling an H I column density measurement. New Magellan/FIRE spectra detect Na I D, Mg II, Mg I, and Fe II in the quasar spectrum and tie their column densities to N(H I), delivering empirical conversions usable for JWST-selected neutral outflows. The Na I calibration is just ~30% below the Milky Way relation commonly assumed at high z, supporting large neutral mass outflow estimates relevant to quenching. In contrast, applying the local Mg II calibration would err by an order of magnitude, likely due to dust depletion variations.

outflows high-z spectroscopy

2025-07-08 · 2507.06339v1

High-Resolution Optical IFU Spectroscopy of the Complex Galaxy Merger II Zw 096

C. Riesco, E. Treister, G. Venturi, et al.

Download highlighted PDF arXiv abstract

Using VLT/MUSE in both NFM and WFM, this work resolves II Zw 096 into three or more interacting galaxies and maps ionized-gas morphology, kinematics, and excitation across the system. Velocity fields show rotation with strong deviations and widespread shocks, consistent with a collapsing small-group scenario and intense star formation. A compact D1 knot (≤175 pc) that contributes 40–70% of the IR luminosity shows strong multiwavelength evidence for a heavily obscured AGN. Multi-component fits to Hα+[N II] and continuum mapping clarify the internal structure and current merger stage.

obscured AGN low-z spectroscopy

2025-07-07 · 2507.05381v1

Escape fractions from unattenuated Ly$α$ emitters around luminous $z>6$ quasars

Minghao Yue, Anna-Christina Eilers, Jorryt Matthee, et al.

Download highlighted PDF arXiv abstract

JWST/NIRSpec-MSA spectroscopy in the J0100+2802 and J1148+5251 fields measures Lyα for 50 galaxies at 6<z<7 (median M_UV=−19.97), including 15 within Δv<2500 km s−1 of the quasars. Galaxies in the quasar proximity zones show clear blue-side Lyα flux and higher equivalent widths than similar-redshift field galaxies, implying little to no evolution in the LAE fraction from z≈6.4 to z≈5. Using the low IGM opacity near the quasars, the authors infer an average Lyα escape fraction of 0.14±0.04 at ⟨z⟩≈6.4. This supports reionization scenarios with low LyC escape in luminous galaxies (f_esc^LyC≲0.1), suggesting bright galaxies contribute modestly to the ionizing budget.

luminous quasar high-z reionization spectroscopy

2025-07-07 · 2507.05354v1

JWST MIRI/MRS observations of hot molecular gas in an AGN host galaxy at Cosmic Noon

D. Kakkad, V. Mainieri, Takumi S. Tanaka, et al.

Download highlighted PDF arXiv abstract

Using JWST/MIRI MRS, the authors detect ro‑vibrational H2 in the z≈2.2 X‑ray AGN cid_346, measuring 1‑0 S(1) (and S(0)) and inferring a hot H2 mass of ≈8×10^5 M⊙. They map hot molecular emission and CO(3‑2) to >10 kpc, and NIRCam imaging reveals two nearby satellites at ≈3.3 and 7.4 kpc, pointing to an interacting environment. The hot phase is 10^5–10^6× less massive than the cold reservoir, but the authors argue H2 ro‑vibrational lines effectively trace locally heated/shocked gas where CO may be faint. Ionized gas shows [O III] extension and a blue wing toward the SE, consistent with outflow activity shaping the multiphase medium.

JWST AGN X-ray outflows ALMA/mm spectroscopy

2025-07-02 · 2507.01952v1

The Lockman-SpReSO project. Spectroscopic analysis of Type 1 AGN

Castalia Alenka Negrete, Hector J. Ibarra-Medel, Erika Benitez, et al.

Download highlighted PDF arXiv abstract

First optical–UV spectral analysis of 30 faint (mB=19.6–21.8) Type 1 AGN from the Lockman‑SpReSO survey spanning 0.33<z<4.97, using Quasar Main Sequence–based deblending of the principal UV/optical broad‑line regions. Derived ranges are 44.85<log Lbol<47.87, 7.59<log MBH<9.80, and −1.70<log REdd<0.56; 18 high‑z sources fall in Population B, with a few A/B1/B1+ at low z, and none are extreme accretors. CIV c(1/2) indicates modest winds (941 to −1587 km s−1) and the Baldwin effect shows a slope of −0.23±0.03, consistent with comparable samples. Twelve spectra overlap with SDSS DR17 and show no variability, providing a stable benchmark for FIR/X‑ray–selected quasar demographics.

broad-line AGN spectroscopy X-ray QSO

2025-07-02 · 2507.01355v1

The birth of young radio jets in changing-look AGN: a population study

Sufia Birmingham, Charlotte Ward, Kristina Nyland, et al.

Download highlighted PDF arXiv abstract

A population study of 474 spectroscopically confirmed changing-look AGN tracks their radio behavior with ASKAP VAST and VLASS to test whether optical state changes spawn newborn radio jets. Across 20 VAST-detected CLAGN, the authors see no Mrk 590– or 1ES 1927+654–like radio fading within ~10 years of the changing-look epoch, and for six low‑z, high‑mass objects they rule out a Mrk 590–like flare. Population-wide, CLAGN show higher VAST/VLASS detection and 1 GHz variability rates but lower radio‑loud fractions than a control AGN sample, and VLA SEDs plus Magellan spectra do not support a link to VLASS sources that transitioned from radio‑quiet to radio‑loud. The results imply enhanced accretion episodes often stir compact radio activity but rarely mirror the decadal jet turn‑on channel seen in RL-transition systems, constraining when and how young radio jets are born.

radio variability broad Balmer broad-line AGN spectroscopy

2025-06-26 · 2506.20896v1

Blowing star formation away in AGN Hosts (BAH) -- IV: Feeding and feedback in 3C 293 observed with JWST NIRSpec

Maitê S. Z. de Mellos, Rogemar A. Riffel, Gabriel L. Souza-Oliveira, et al.

Download highlighted PDF arXiv abstract

JWST/NIRSpec IFU mapping of 3C 293’s inner ~2 kpc separates the gas into a rotating disk (σ ~100 km s−1), a blueshifted broad outflow (σ ~250 km s−1), and a very broad ionized outflow (σ ~640 km s−1). H2 2.12 μm, [Fe II] 1.64 μm, and Paα trace multiphase flows through heavy dust (A_V up to ~35), with H2 inflow along dust lanes at Ṁ_in ~4×10−4 M⊙ yr−1. Peak outflow rates reach 0.08±0.02 M⊙ yr−1 (hot H2) and 6.5±1.7 M⊙ yr−1 (ionized), and the jet-driven outflow carries ≈5% of the radio-jet power—sufficient to suppress star formation. The stellar field is a rotating disk whose kinematic center is offset by ~0.5 arcsec from the NIR continuum peak, consistent with a disturbed, post-merger nucleus.

JWST AGN outflows obscured AGN radio spectroscopy low-z

2025-06-17 · 2506.14870v1

JADES and BlackTHUNDER: rest-frame Balmer-line absorption and the local environment in a Little Red Dot at z = 5

Francesco D'Eugenio, Ignas Juodžbalis, Xihan Ji, et al.

Download highlighted PDF arXiv abstract

Reports a broad-line Little Red Dot at z=5.077 (JADES-GS+033223.41-275404.5/159717) with NIRSpec MSA+IFU, revealing multi-component Hα including two broad Gaussians. A virial black hole mass of log(MBH/M⊙)=7.65 and a narrow [O III] λ5007-based dynamical mass of log(Mdyn/M⊙)=9.1 imply a BH overmassive relative to its host. The source sits in a 7-kpc pool of ionized gas with three neighbors (a satellite, a possible satellite/gas cloud, and a tentatively detected spatially detached outflow). A deep rest-frame Hα absorber (deeper than the continuum; v=-13 km s−1, σ=120 km s−1) appears in G395H but not G395M, with tentative EW variability over two rest-frame months (2.6σ), underscoring resolution- and time-dependent incidence of absorbers in LRDs.

LRD broad Balmer overmassive BH spectroscopy outflows variability

2025-06-16 · 2506.13945v1

Euclid: The potential of slitless infrared spectroscopy: A z=5.4 quasar and new ultracool dwarfs

E. Bañados, V. Le Brun, S. Belladitta, et al.

Download highlighted PDF arXiv abstract

Euclid NISP slitless spectra demonstrate blind, space-based identification of both high‑z quasars and their chief photometric contaminants, ultracool dwarfs. The team reports a bright z=5.404 quasar, EUCL J181530.01+652054.0, flagged by strong broad CIII] and MgII in RGE (1206–1892 nm) with CIV/CIII] also in BGE (926–1366 nm) and confirmed by LBT optical data. It is a high‑excitation BAL quasar detected by LOFAR at 144 MHz (L144≈4×10^25 W/Hz), with Lbol≈3×10^12 Lsun and MBH≈3.4×10^9 Msun—an unexpectedly luminous find within only ~20 deg2. Cross-correlation of NISP spectra likewise yields new ultracool dwarfs (e.g., T3 EUCL J002516.31+491618.5; M6 EUCL J174429.80+672728.1), underscoring RGE’s ability to uncover bright quasars at z~5.5 and z>7 where photometric selection struggles.

luminous quasar QSO high-z spectroscopy radio

2025-06-13 · 2506.12141v1

A big red dot at cosmic noon

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

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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

2025-06-05 · 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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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

2025-06-03 · 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.

Download highlighted PDF arXiv abstract

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

2025-05-28 · 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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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 · 2505.20393v1

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.

Download highlighted PDF arXiv abstract

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

2025-05-21 · 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.

Download highlighted PDF arXiv abstract

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 · 2505.14676v1

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

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

Download highlighted PDF arXiv abstract

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.

arXiv abstract

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.

Download highlighted PDF arXiv abstract

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 · 2505.09542v1

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.

Download highlighted PDF arXiv abstract

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 · 2505.08870v1

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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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

2025-05-09 · 2505.06359v1

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

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

Download highlighted PDF arXiv abstract

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 · 2505.05942v1

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

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

Download highlighted PDF arXiv abstract

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

2025-05-07 · 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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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

2025-05-05 · 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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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

2025-04-15 · 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.

Download highlighted PDF arXiv abstract

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 · 2504.10596v1

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.

Download highlighted PDF arXiv abstract

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 · 2504.10573v1

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

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

Download highlighted PDF arXiv abstract

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 · 2504.08039v1

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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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.

arXiv abstract

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.

Download highlighted PDF arXiv abstract

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

2025-04-03 · 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.

Download highlighted PDF arXiv abstract

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.

Download highlighted PDF arXiv abstract

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

2025-04-01 · 2504.01103v1

JWST reveals the diversity of nuclear obscuring dust in nearby AGN: nuclear isolation of MIRI/MRS datacubes and continuum spectral fitting

Omaira González-Martín, Daniel J. Díaz-González, Mariela Martínez-Paredes, et al.

Download highlighted PDF arXiv abstract

The authors PSF-isolate nuclear mid-IR emission in 21 nearby (z<0.05) AGN with a new tool (MRSPSFisol) and fit the continuum using multiple dust libraries. Twelve nuclei achieve good fits (chi2/dof<2), typically with a flared-disk model combining clumpy and smooth dust and allowing grain size to vary; two prefer disk+wind and one the classical clumpy torus. About 40% resist all models because of extreme silicate profiles plus pervasive water-ice and aliphatic hydrocarbon absorption, pointing to missing chemistry. This establishes JWST/MRS as a clean nuclear isolator and shows that next-generation dust models must capture more complex compositions.

JWST AGN obscured AGN spectroscopy low-z

2025-04-01 · 2504.01079v1

HI 21-cm Absorption Associated with Foreground Galaxies on Top of Quasars

Labanya Kumar Guha, Raghunathan Srianand, Rajeshwari Dutta

arXiv abstract

Pilot uGMRT 21-cm searches toward three SDSS-identified Galaxies On Top Of Quasars (J0758+1136, J1159+5820, J1451+0857) yield a 100% detection rate of HI absorption at extremely small impact parameters. Combining with literature, the authors argue GOTOQs form a distinct absorber population with much higher detection rates than DLA- or metal-selected samples. They find a Milky Way–like reddening relation, ∫τ dv (km s⁻¹) = 13.58(+2.75/−2.35) E(B−V) + 0.68(+1.06/−1.27), and show both detection rate and optical depth drop rapidly with impact parameter. This demonstrates that fiber-selected GOTOQs efficiently trace cold HI close to star-forming galaxies and set the stage for a large, intervening 21-cm absorber sample with upcoming wide-field spectroscopy.

radio spectroscopy QSO

2025-03-21 · 2503.17183v1

Halfway to the Peak: ice absorption bands at $z\approx0.5$ with JWST MIRI/MRS

Anna Sajina, Alexandra Pope, Henrik Spoon, et al.

Download highlighted PDF arXiv abstract

JWST/MIRI–MRS spectroscopy of the dusty starburst–AGN composite SSTXFLS J172458.3+591545 (z=0.494) yields the first combined extragalactic detections of CO2, CO, XCN, and H2O ices, with gas‑phase CO alongside solid CO. Ice-band profiles match Galactic/local templates, and their decomposition (polar‑dominated XCN and CO complexes) plus the silicate depth imply a compact, dense, cold nucleus with n>10^5 cm^-3, T≈20–90 K, and A_V≈6–7; [NeV]/[NeVI] confirm a deeply buried AGN. The authors introduce τ_Si versus τ_CO2/τ_Si as a diagnostic that jointly traces total dustiness and dust clumpiness along the line of sight. Together, these results showcase MIRI’s power to map dust composition and geometry well beyond the local Universe.

obscured AGN spectroscopy low-z

2025-03-20 · 2503.16600v1

A remarkable Ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a Little Red Dot at $z=3.5$

Anna de Graaff, Hans-Walter Rix, Rohan P. Naidu, et al.

Download highlighted PDF arXiv abstract

JWST/NIRSpec+NIRCam+MIRI data on The Cliff, a luminous Little Red Dot at z=3.55, reveal an extreme Balmer break—about twice stronger than any previously seen at high-z—alongside broad Hα (FWHM∼1500 km s⁻¹) and He I emission but no significant metal lines. Stellar-population solutions (even with steep dust or IMF tweaks) fail, and their formal M*∼10^10.5 M⊙ with re∼40 pc would imply implausibly high stellar-collision rates. The spectra and continuum are instead best matched by a “black hole star” configuration: a powerful central ionizing source embedded in dense, absorbing gas that imprints the Balmer edge and Hα absorption while favoring an intrinsically red continuum over heavy dust. This makes The Cliff compelling evidence that at least some LRDs are not ultra-dense galaxies but compact, accretion-powered nuclei shrouded by dense gas.

LRD broad Balmer stellar envelope super-Eddington spectroscopy high-z

2025-03-19 · 2503.15317v1

Euclid Quick Data Release (Q1). First Euclid statistical study of galaxy mergers and their connection to active galactic nuclei

Euclid Collaboration, A. La Marca, L. Wang, et al.

Download highlighted PDF arXiv abstract

Using Euclid Q1 Deep Fields, the team builds a stellar‑mass–complete (M*>10^9.8 Msun) sample at 0.5<z<2, identifies major mergers with CNNs trained on simulations, and selects AGN via X‑ray, optical spectroscopy, MIR colours, and I_E‑band PSF decompositions. Across all AGN selections, mergers host an AGN excess by factors of 2–6, and the AGN merger fraction rises with point‑source contribution f_PSF up to ~0.55 before declining. In luminosity terms, f_merg increases with L_PSF, exceeding 50% for L_PSF>2×10^43 erg/s at z<0.9 and becoming dominant only above ~10^45 erg/s at z>0.9; for X‑ray AGN, f_merg also increases with L_bol, with AGN mostly in mergers at L_bol>10^45 erg/s. This ties major mergers to the most powerful, dust‑obscured SMBH growth phases, with spectroscopic trends weaker due to small samples.

demographics obscured AGN X-ray spectroscopy

2025-03-18 · 2503.14739v1

DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest

DESI Collaboration, M. Abdul-Karim, J. Aguilar, et al.

Download highlighted PDF arXiv abstract

DESI DR2 doubles the Lyα-forest dataset over DR1, analyzing both the Lyα auto-correlation and the Lyα–QSO cross-correlation from >820k quasar spectra and >1.2M quasar positions. It delivers sub‑percent BAO distances at zeff=2.33: 1.1% radial and 1.3% transverse, for 0.65% isotropic precision, measuring DH/rd=8.632±0.098(stat)±0.026(sys) and DM/rd=38.99±0.52(stat)±0.12(sys). The team details analysis upgrades, validation on improved synthetic data, and refined DLA identification. Motivated by nonlinear BAO shift studies, they include—for the first time in Lyα BAO—a dedicated systematic error term, strengthening high‑z expansion constraints.

QSO high-z spectroscopy

2025-03-14 · 2503.11752v1

BlackTHUNDER strikes twice: rest-frame Balmer-line absorption and high Eddington accretion rate in a Little Red Dot at $z=7.04$

Francesco D'Eugenio, Roberto Maiolino, Michele Perna, et al.

Download highlighted PDF arXiv abstract

BlackTHUNDER re-analyzes JWST/NIRSpec-IFS G395H data for the Little Red Dot Abell2744-QSO1 at z=7.04, focusing on the Hα region. The Hα profile is distinctly non-Gaussian, requiring at least two broad Gaussians plus a narrow component, and shows strong rest-frame Balmer-line absorption (EW ≈22 Å) centered at the systemic velocity of the broad line; the absorber’s dispersion (σ_abs ≈110 km s⁻¹) matches that inferred from the Balmer break, arguing for a long‑lived, non-flowing structure. An Hα-based virial mass of log(MBH/M⊙) ≈7.2 and a deconvolved narrow-line width σ_n ≈22 km s⁻¹ yield MBH/Mdyn = 0.15–1.2, confirming an overmassive black hole with limited room for a host galaxy. The revised mass implies high accretion, λ_Edd ≈0.7–1.6 (potentially super‑Eddington at the low‑mass end), tying Balmer-break strength directly to Balmer-line absorption in LRDs.

LRD broad Balmer stellar envelope overmassive BH super-Eddington spectroscopy

2025-03-10 · 2503.07074v1

JWST ASPIRE: How Did Galaxies Complete Reionization? Evidence for Excess IGM Transmission around ${\rm [O\,{\scriptstyle III}]}$ Emitters during Reionization

Koki Kakiichi, Xiangyu Jin, Feige Wang, et al.

Download highlighted PDF arXiv abstract

ASPIRE cross-correlates [O III] emitters from NIRCam/F356W grism with Lyα-forest pixels in five z>6.5 QSO fields (5.4<z<6.5). It finds 2σ excess Lyα transmission at ~20–40 cMpc around [O III] emitters (z=5.86) with small-scale absorption, implying highly ionized bubbles around galaxies embedded in overdense environments. Comparing to THESAN, the signal points to >50 cMpc ionized regions and a stronger UV background supplied by unseen faint galaxies; the observed [O III] sources near individual transmission spikes cannot by themselves maintain the ionization even if all hosted AGN with 100% LyC escape. Simulations underpredict the excess transmission, hinting at larger bubbles or stronger UV/temperature fluctuations, with current uncertainties dominated by cosmic variance.

reionization high-z spectroscopy simulation