654 indexed papers · 430 research notes

Research archive

2025-05-11 · 2505.06965v1

Black Hole Envelopes in Little Red Dots

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

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

2025-04-09 · 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

2025-03-19 · 2503.15323v1

Euclid Quick Data Release (Q1). Extending the quest for little red dots to z<4

Euclid Collaboration, L. Bisigello, G. Rodighiero, et al.

Download highlighted PDF arXiv abstract

Using 63 deg² from Euclid’s Quick Data Release (Q1) plus IRAC and ground-based griz, the team fits two power laws to photometry to isolate little red dots with blue UV and red optical slopes while removing extended sources, strong line emitters, and artifacts. They assemble 3341 LRD candidates at z=0.33–3.6 (29 with IRAC), and derive a rest‑frame UV luminosity function that rises from high z down to z≈1.5–2.5 before declining toward lower redshift. Comparing to quasar UV LFs shows LRDs are not the dominant AGN population at z<4 for M_UV<-21. A noted caveat is that evolution inferred from the IRAC‑detected subsample is limited by small numbers and IRAC’s resolution, motivating follow‑up.

LRD v-shaped SED demographics low-z

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.

Download highlighted PDF arXiv abstract

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

2025-01-22 · 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