654 indexed papers · 430 research notes

Research archive

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

2025-05-05 · 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

2025-04-10 · 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

2025-04-04 · 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

2025-03-20 · 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.

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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

2025-03-20 · 2503.16596v1

A "Black Hole Star" Reveals the Remarkable Gas-Enshrouded Hearts of the Little Red Dots

Rohan P. Naidu, Jorryt Matthee, Harley Katz, et al.

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JWST/NIRSpec spectroscopy of the point-like source MoM-BH*-1, observed ~660 Myr after the Big Bang, reveals an enormous Balmer break, broad multi-peaked Hβ, and deep Balmer-line absorption. The authors model it as a “black hole star”: a supermassive black hole enshrouded by extremely dense, turbulent, dust-free gas whose atmosphere imprints the break and absorption while dominating the observed light; narrow [OIII] and residual UV are attributed to a faint host. The data are well matched by a simple Cloudy setup that reproduces the break strength, Balmer EWs, UV faintness, and MIRI continuum, with line ratios consistent with high densities that can collisionally suppress [OIII] and a hint of variability reinforcing the SMBH interpretation. They further argue that Little Red Dots can be explained as BH*s embedded in comparably bright hosts, implying current LRD black hole masses—derived with steep dust corrections and standard scaling relations—may be overestimated by orders of magnitude.

LRD BH seeds super-Eddington stellar envelope broad Balmer high-z

2025-03-20 · 2503.16595v1

Little red dots as young supermassive black holes in dense ionized cocoons

V. Rusakov, D. Watson, G. P. Nikopoulos, et al.

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Using the highest-S/N JWST/NIRSpec spectra of LRD-like broad-line sources, the authors show that Balmer-line wings are exponential and symmetric, as expected from electron scattering in a compact, Compton-thick ionized cocoon. Convolving a narrow Doppler core with this scattering kernel yields intrinsic widths of only a few hundred km/s, implying black holes of ~10^5–10^7 M⊙ accreting near the Eddington limit within light‑day–scale gas with mild outflows. Accounting for scattering lowers previous mass estimates by ~2 dex and naturally explains LRD traits, including very weak X-ray/radio via nebular reprocessing. This reframes LRDs as young, rapidly growing SMBHs rather than overmassive quasars for their hosts.

LRD broad Balmer nebular continuum super-Eddington high-z

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.

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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

2025-03-04 · 2503.02942v1

Spectroscopic AGN survey at $z$ $\sim$ 2 with NTT/SOFI for GRAVITY+ observations

D. J. D. Santos, T. Shimizu, R. Davies, et al.

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NTT/SOFI K-band spectroscopy vets 29 z≈2 type 1 quasars for GRAVITY+, measuring Hα fluxes and Balmer-line shapes to preview BLR kinematics. The Balmer profiles are strongly non-Gaussian with narrow cores plus broad wings, consistent with rotation plus turbulence or a two-zone BLR; two objects show tentative radial-motion dominance. Low FWHM/σ ratios yield small Hα virial factors, cautioning that single-epoch mass scalings can under-estimate MBH for these profiles. Predicted differential-phase signals guide VLTI/GRAVITY+ strategies to secure dynamical BLR masses at cosmic noon.

broad-line AGN QSO broad Balmer spectroscopy

2025-03-03 · 2503.02059v1

A confirmed deficit of hot and cold dust emission in the most luminous Little Red Dots

David J. Setton, Jenny E. Greene, Justin S. Spilker, et al.

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Deep MIRI imaging plus new ALMA continuum and [C II] spectroscopy on two luminous LRDs at z=3.1 (A2744-45924) and z=4.47 (RUBIES-BLAGN-1) set the tightest IR constraints yet. Rest-frame 1–4 μm detections show a flat IR slope, excluding hot (T≳500 K) dust, while far-IR non-detections exclude a cold (T≲75 K) component and typical [C II]-bright dusty starbursts. Empirical maximal SEDs require log(L_IR/L_sun) ≲ 12.2 (3σ), in strong tension with energy-balance predictions from reddened galaxy, AGN, or composite fits. The authors favor intrinsically red LRD SEDs over heavily dust-reddened blue engines, reshaping how these compact sources are interpreted.

LRD ALMA/mm v-shaped SED broad Balmer spectroscopy

2025-03-03 · 2503.01945v1

No [CII] or dust detection in two Little Red Dots at z$_{\rm spec}$ > 7

Mengyuan Xiao, Pascal A. Oesch, Longji Bing, et al.

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Two z_spec > 7 Little Red Dots in FRESCO GOODS-N (ID9094, ID2756) show v‑shape colors, compact morphologies, and broad Hβ (FWHM 2280±490 and 1070±240 km/s), marking them as Type‑I AGN candidates. Deep NOEMA follow-up finds no [CII] 158 μm or 1.3 mm continuum; a DSFG interpretation would have yielded strong detections (>16σ [CII] and >3σ 1.3 mm for ID9094; >5σ [CII] for ID2756). Using the 3σ FIR limits in UV–FIR SED fitting (with/without AGN) and comparison to the L_[CII]–SFR_tot relation, the data favor an AGN contribution, as a dust‑only model would require unusually high dust temperatures. The work shows FIR non‑detections can discriminate AGN‑dominated LRDs from DSFG impostors at z > 7, though a purely dusty origin cannot be fully excluded.

LRD v-shaped SED broad Balmer ALMA/mm spectroscopy high-z

2025-02-27 · 2502.20550v1

JWST's PEARLS: A z=6 quasar in a train-wreck galaxy merger system

Madeline A. Marshall, Rogier A. Windhorst, Giovanni Ferrami, et al.

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JWST/NIRSpec IFU prism data (0.6–5.3 μm, R≈100) on the z=5.89 quasar NDWFS J1425+3254 capture rest-UV/optical lines and spatially resolve its host environment. Broad Hα and Hβ yield MBH≈1.4×10^9 M⊙ and Lbol/LEdd≈0.3, while [O III] exposes a quasar-driven outflow with v≈6050 km s−1 and an ionized outflow rate ≈1650 M⊙ yr−1. The cube maps a “train-wreck” triple merger: an older, massive NE companion (M⋆≈3.6×10^11 M⊙, age≈65 Myr) linked to the host by a gas bridge, plus a very young SE companion (age≈6.7 Myr, M⋆≈1.9×10^10 M⊙) with ongoing star formation. These results argue for merger-triggered early SMBH growth; a likely foreground z=1.135 galaxy may modestly lens the quasar (1<μ<2; <0.75 mag).

luminous quasar QSO high-z broad Balmer outflows spectroscopy

2025-02-18 · 2502.12664v1

Where to search for supermassive binary black holes

Paola Marziani, Edi Bon, Natasa Bon, et al.

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This note argues that the best hunting ground for supermassive binary black holes is a specific, evolved segment of the quasar main sequence—Population B/B1 sources with weak Fe II and broad Balmer lines—where BLR kinematics most clearly betray companions. On a flux-limited sample, the authors decompose Hβ and Mg II with broad/very-broad components and measure centroids at multiple fractional intensities, finding characteristic offsets and asymmetries suggestive of perturbed BLR dynamics. In the M•–L plane, these targets cluster at low Eddington ratios (Population B), reinforcing a focused search strategy. They advocate time-domain spectroscopy to confirm periodic profile changes, cautioning that photometric periodicities alone are vulnerable to red-noise false positives.

broad Balmer QSO variability spectroscopy

2025-02-11 · 2502.07875v1

Investigating photometric and spectroscopic variability in the multiply-imaged Little Red Dot A2744-QSO1

Lukas J. Furtak, Amy R. Secunda, Jenny E. Greene, et al.

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Exploiting the three lensed images of the z=7.045 LRD A2744-QSO1 with 22 yr (observer; 2.7 yr rest) delays, the authors test variability using two NIRSpec epochs and multi-epoch NIRCam. Magnification-insensitive EWs of broad Hα and Hβ vary by up to 18±3% and 22±8%, respectively, over 875 d (2.4 yr) in the rest frame, coherently across images. No significant broadband photometric variability is detected beyond ≈0.3 mag systematics, so the EW changes cannot yet be tied to line- versus continuum-driven variability. A DRW model for MBH≈4×10^7 M⊙ matches the sparse sampling, bolstering the AGN interpretation and motivating continued monitoring.

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

2025-01-22 · 2501.13082v1

BlackTHUNDER -- A non-stellar Balmer break in a black hole-dominated little red dot at $z=7.04$

Xihan Ji, Roberto Maiolino, Hannah Übler, et al.

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BlackTHUNDER analyzes JWST NIRSpec-IFU plus archival MSA data of the triply imaged lensed LRD Abell2744-QSO1 at z=7.04, confirming a smooth Balmer break and a broad Hβ from the BLR. The narrow Hβ dispersion gives M_dyn < 4×10^8 Msun, capping the stellar contribution to <10% of the optical continuum and favoring a non-stellar Balmer break produced by an AGN continuum filtered by very dense (n_H ~ 10^10 cm^-3), nearly dust-free gas likely in/around the BLR; a tentative 3σ Hβ absorption appears in the R2700 spectrum. The black hole is overmassive relative to both stellar and dynamical masses, with hints of variability and an initial reverberation-mapping attempt. This picture alleviates the extreme stellar-density problem for LRDs and may generalize to similar V-shaped continua.

LRD v-shaped SED broad Balmer overmassive BH spectroscopy high-z

2025-01-17 · 2501.10574v1

A Large Systematic Search for Close Supermassive Binary and Rapidly Recoiling Black Holes -- IV. Ultraviolet spectroscopy

Jessie C. Runnoe, Michael Eracleous, Tamara Bogdanović, et al.

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HST UV spectra (COS/STIS) for 13 z<0.7 quasars with large H-beta velocity offsets are compared to contemporaneous optical Balmer profiles to test supermassive black hole binary (SBHB) versus single-BH disk-like BLR scenarios. The authors isolate broad components and ask whether UV resonance lines (e.g., Lyα, C IV) share the same velocity offset as Balmer lines set by [O III]. They find three objects with strong SBHB support, five tentative, one disfavored, and four inconclusive due to severely absorbed UV profiles. This cross-wavelength line-profile test tightens SBHB vetting by demanding consistent Doppler shifts across independent broad lines.

QSO broad-line AGN broad Balmer spectroscopy low-z

2025-01-06 · 2501.03309v1

Little Red Dots are Tidal Disruption Events in Runaway-Collapsing Clusters

Jillian Bellovary

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Proposes that Little Red Dots are recurrent tidal disruption events triggered during runaway collapse of the first dense star clusters, forming intermediate-mass black hole seeds. Matching JWST LRD number densities to seed-formation predictions implies a required TDE rate of ~10^-4 yr^-1; analytic (loss-cone) and simulation-based scalings show this rate is feasible in dense clusters. The scenario naturally explains compact, UV-bright emission with broad H-alpha and links LRDs to early black-hole growth. A top-heavy IMF may be needed to satisfy ΛCDM mass-function limits, and the hypothesis is testable via TDE-like variability in JWST follow-up.

LRD BH seeds broad Balmer variability