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

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Peer-reviewed

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Abstract

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="http://www.w3.org/1998/Math/MathML" 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="http://www.w3.org/1998/Math/MathML" 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>

Description

Keywords

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

Journal Title

The Astrophysical Journal

Conference Name

Journal ISSN

0004-637X
1538-4357

Volume Title

968

Publisher

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