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arxiv: 2401.08782 · v2 · pith:TQV6YPOZnew · submitted 2024-01-16 · 🌌 astro-ph.GA · astro-ph.IM

What is the nature of Little Red Dots and what is not, MIRI SMILES edition

classification 🌌 astro-ph.GA astro-ph.IM
keywords miriemissionspectralstarsstellardustlrdsmid-infrared
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We study little red dots (LRD) detected by JADES and covered by the SMILES MIRI survey. Our sample contains 31 sources, $\sim70$% detected in the two bluest MIRI bands, 40% in redder filters. The median/quartiles redshifts are $z=6.9_{5.9}^{7.7}$ (55% spectroscopic). We analyze the rest-frame ultraviolet through near/mid-infrared spectral energy distributions of LRDs combining NIRCam and MIRI observations, using a variety of modeling techniques that include emission from stars, dust, and (un)obscured active galactic nuclei (AGN). The NIRCam$-$MIRI colors, for $\geq10$ $\mu$m, are bluer than direct pure emission from AGN tori; the spectral slope flattens in the rest-frame near-infrared, consistent with a 1.6 $\mu$m stellar bump. Both observations imply that stellar emission makes the dominant contribution at these wavelengths, expediting a stellar mass estimation: the median/quartiles are $\log \mathrm{M_\star/M_\odot}=9.4_{9.1}^{9.7}$. The number density of LRDs is $10^{-4.0\pm0.1}$ Mpc$^{-3}$, accounting for $14\pm3$% of the global population of galaxies with similar redshifts and masses. The flat ultraviolet spectral range is dominated by young stars. The rest-frame near/mid-infrared (2-4 $\mu$m) spectral slope reveals significant amounts of dust (bolometric stellar attenuation $\sim3-4$ mag) heated by strong radiation fields arising from highly embedded compact sources. Our models imply $<0.4$ kpc heating knots, containing dust-enshrouded OB stars or an AGN producing a similar radiation field, obscured by $\mathrm{A(V)}>10$ mag. We conclude that LRDs are extremely intense and compact starburst galaxies with mass-weighted ages 5-10 Myr, very efficient in producing dust, their global energy output dominated by the direct and dust-recycled emission from OB stars, with some contribution from obscured AGN in the mid-infrared.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Little red dots as a cosmological probe: constraining $H_0$ with quasi-periodic pulsations

    astro-ph.GA 2026-06 unverdicted novelty 7.0

    Derives idealized P-L-T relation from hydrostatic envelope model for LRDs and uses sparse data to obtain preliminary H0 = 120.7 with large errors as proof-of-concept.

  2. Hidden in Pixels I: Discovery of dual "little red dots" indicates excess clustering on kilo-parsec scales

    astro-ph.GA 2024-12 unverdicted novelty 7.0

    Four dual LRD candidates at z~5.5 with kpc separations show 20-30x excess sub-arcsec clustering versus extrapolated AGN ACF, implying merger-driven SMBH growth.