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

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arxiv 2401.08782 v2 pith:TQV6YPOZ submitted 2024-01-16 astro-ph.GA astro-ph.IM

classification astro-ph.GAastro-ph.IM
keywords miriemissionspectralstarsstellardustlrdsmid-infrared
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abstract

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 3 Pith papers

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

  1. Where did all the Little Red Dots go? The abundance of LRD analogues among objects with broad lines at $z < 0.35$

    astro-ph.GA 2026-08 conditional novelty 6.0 of 10

    Only 0.08% of low-redshift broad-line objects have SEDs resembling high-redshift Little Red Dots, yielding nine candidates, one of which is the known analogue 'The Egg'.

  2. Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions

    astro-ph.GA 2025-06 conditional novelty 6.0 of 10

    Little red dots sit in lower-density environments than typical galaxies, and Bayesian model comparison favors non-AGN interpretations for most of them.

  3. Little Red reionization factories

    astro-ph.GA 2025-08 unverdicted novelty 4.0 of 10

    LRDs may drive cosmic reionization: tidal fields are said to funnel intergalactic hydrogen into colliding streams at LRD sites, igniting starbursts that ionize the gas.

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