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What Is the Nature of Little Red Dots and what Is Not, MIRI SMILES Edition

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jats:titleAbstract</jats:title> jats:pWe 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 jats:inline-formula jats:tex-math

</jats:tex-math> <mml:math xmlns:mml="" overflow="scroll"> mml:miz</mml:mi> mml:mo=</mml:mo> mml:msubsup mml:mrow mml:mn6.9</mml:mn> </mml:mrow> mml:mrow mml:mn5.9</mml:mn> </mml:mrow> mml:mrow mml:mn7.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> </jats:inline-formula> (55% spectroscopic). The spectral slopes flatten in the rest-frame near-infrared, consistent with a 1.6 jats:italicμ</jats:italic>m 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 jats:inline-formula jats:tex-math

</jats:tex-math> <mml:math xmlns:mml="" overflow="scroll"> mml:milog</mml:mi> mml:msub mml:mrow mml:miM</mml:mi> </mml:mrow> mml:mrow mml:mo⋆</mml:mo> </mml:mrow> </mml:msub> mml:mrow <mml:mo stretchy="true">/</mml:mo> </mml:mrow> mml:msub mml:mrow mml:miM</mml:mi> </mml:mrow> mml:mrow mml:mo⊙</mml:mo> </mml:mrow> </mml:msub> mml:mo=</mml:mo> mml:msubsup mml:mrow mml:mn9.4</mml:mn> </mml:mrow> mml:mrow mml:mn9.1</mml:mn> </mml:mrow> mml:mrow mml:mn9.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> </jats:inline-formula>. The number density of LRDs is 10jats:sup−4.0±0.1</jats:sup> Mpcjats:sup−3</jats:sup>, accounting for 14% ± 3% of the global population of galaxies with similar redshifts and masses. The rest-frame near-/mid-infrared (2–4 jats:italicμ</jats:italic>m) 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 jats:italicA</jats:italic>(jats:italicV</jats:italic>) > 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).</jats:p>



High-redshift galaxies, Galaxy stellar content, Broad band photometry, Active galactic nuclei, Galaxy formation, Stellar populations, Galaxy evolution, Galaxy ages, James Webb Space Telescope

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The Astrophysical Journal

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American Astronomical Society
MEC ∣ Agencia Estatal de Investigación (AEI) (PID022-139567NB-I00)