What Is the Nature of Little Red Dots and what Is Not, MIRI SMILES Edition
Barro, Guillermo;
Pérez-González, Pablo G.;
Bunker, Andrew J.;
Rodríguez Del Pino, Bruno;
Willott, Chris;
Johnson, Benjamin D.;
Ji, Zhiyuan;
Shivaei, Irene;
Lyu, Jianwei;
Rieke, George H.;
Annunziatella, Marianna;
Alberts, Stacey;
Egami, Eiichi;
Hainline, Kevin;
Rieke, Marcia;
Sun, Fengwu;
Tacchella, Sandro;
Williams, Christina C.;
Willmer, Christopher N. A.;
Baker, William M.;
Rujopakarn, Wiphu;
Robertson, Brant;
Puskás, Dávid
Spain, United States, United Kingdom, Thailand, Canada
Abstract
We study 31 little red dots (LRD) detected by JADES/NIRCam and covered by the SMILES/MIRI survey, of which ∼70% are detected in the two bluest MIRI bands and 40% in redder MIRI filters. The median/quartiles redshifts are z=6.95.97.7 (55% spectroscopic). The spectral slopes flatten in the rest-frame near-infrared, consistent with a 1.6 μm stellar bump but bluer than direct pure emission from active galactic nuclei (AGN) tori. The apparent dominance of stellar emission at these wavelengths for many LRDs expedites stellar mass estimation: the median/quartiles are logM⋆/M⊙=9.49.19.7 . The number density of LRDs is 10‑4.0±0.1 Mpc‑3, accounting for 14% ± 3% of the global population of galaxies with similar redshifts and masses. The rest-frame near-/mid-infrared (2–4 μm) spectral slope reveals significant amounts of warm dust (bolometric attenuation ∼3–4 mag). Our spectral energy distribution modeling implies the presence of <0.4 kpc diameter knots, heated by either dust-enshrouded OB stars or an AGN producing a similar radiation field, obscured by A(V) > 10 mag. We find a wide variety in the nature of LRDs. However, the best-fitting models for many of them correspond to extremely intense and compact starburst galaxies with mass-weighted ages 5–10 Myr, very efficient in producing dust, with their global energy output dominated by the direct (in the flat rest-frame ultraviolet and optical spectral range) and dust-recycled emission from OB stars with some contribution from an obscured AGN (in the infrared).
2024
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The Astrophysical Journal
JWST
eHST
117
