654 indexed papers · 430 research notes

Research archive

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.

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

2025-03-02 · 2503.00998v1

Tentative detection of neutral gas in a Little Red Dot at $z=4.46$

Hollis B. Akins, Caitlin M. Casey, John Chisholm, et al.

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ALMA Band 3/4/5 spectroscopy targets CO(7–6) and [CI](2–1) in three Little Red Dots at z=3.10, 4.46, and 7.04, finding no CO and no far-IR continuum, implying conservative molecular gas limits ≲1–5×10^10 Msun. A2744-45924 (z=4.4655) shows a tentative 4.9σ [CI](2–1) line with a narrow FWHM ~80 km s−1. The [CI]-inferred dynamical mass is ≲10^10 Msun for conservative size assumptions, well below the local MBH–Mdyn relation and an order of magnitude under SED-based stellar mass. If confirmed, this points to LRD hosts unlike massive, gas-rich quasar hosts and lends weight to a non-stellar origin for the Balmer break.

LRD ALMA/mm spectroscopy high-z

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

2025-02-06 · 2502.03742v1

Radio emission from little red dots may reveal their true nature

Muhammad A. Latif, Ammara Aftab, Daniel J. Whalen, et al.

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Using the black-hole fundamental plane alongside star-formation radio scaling, the authors predict continuum fluxes for little red dots (LRDs) across BH mass, X-ray luminosity, SFR, and redshift (≈3–7). They find AGN radio fluxes are typically 10–100× the host stellar contribution at 3–8 GHz, and that a ≥500 nJy detection above 2 GHz at z ≥ 5 or ≥2000 nJy at z = 3–4 would be a clear AGN signature if SFR < 30 M⊙/yr. The analysis implies most LRDs are radio-quiet AGN, consistent with current survey non-detections. Forecasts show ngVLA and SKA could confirm typical LRD AGN in ~10–100 hr integrations, providing a dust-robust discriminator between starbursts and accretion.

LRD radio high-z X-ray

2025-01-29 · 2501.17925v1

Possible environmental quenching in an interacting little red dot pair at $z\sim7$

Rosa M. Mérida, Gaia Gaspar, Marcin Sawicki, et al.

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CANUCS NIRCam imaging behind Abell 370 reveals a compact z∼7 group with two little red dots only 3.3 kpc apart plus three satellites. SEDs show strong Balmer breaks implying recent (~100 Myr) quenching in the LRDs, while the satellites are consistent with a recent-onset (~100 Myr), ongoing burst. Modeling suggests a dust-free AGN produces the UV excess in LRD1 (with the optical dominated by an obscured post‑starburst and a subdominant AGN), and LRD2 is more ambiguous; in this picture the LRDs are massive (~10^10 M⊙, AV>1 mag) and the satellites are lower-mass (10^8–10^9 M⊙) with low attenuation. The tight configuration points to interaction-driven environmental bursting and quenching during reionization.

LRD high-z JWST AGN

2025-01-28 · 2501.16648v1

Three Brown Dwarfs Masquerading as High-Redshift Galaxies in JWST Observations

Zhijun Tu, Shu Wang, Xiaodian Chen, et al.

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From RUBIES NIRSpec PRISM/CLEAR (0.6–5.3 μm) spectra, the authors confirm three compact RUBIES sources (o005_s41280, o006_s00089, o006_s35616) are brown dwarfs rather than distant galaxies. Sonora Elf Owl fits yield Teff ≈2100–2300 K and 1800–2000 K for the two L-dwarf candidates and <1000 K for the late‑T object, with distances around 2 kpc; adding an extinction term notably improves Y/J/H residuals, especially for o006_s35616. NIRCam color–color planes place the cool T dwarf within the little red dot locus while the hotter L dwarfs sit among high‑z galaxy selections, implying ≈0.1% brown‑dwarf contamination in deep extragalactic surveys dominated by L dwarfs. The work pins down how specific substellar SED shapes infiltrate LRD/high‑z samples and shows that low‑resolution prism spectra efficiently weed them out.

LRD spectroscopy

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

2025-01-06 · 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