What is the nature of Little Red Dots and what is not, MIRI SMILES edition
arxiv(2024)
摘要
We study little red dots (LRD) detected by JADES and covered by the SMILES
MIRI survey. Our sample contains 31 sources, ∼70
bluest MIRI bands, 40
z=6.9_5.9^7.7 (55
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 ≥10 μm, are bluer than direct
pure emission from AGN tori; the spectral slope flattens in the rest-frame
near-infrared, consistent with a 1.6 μm stellar bump. Both observations
imply that stellar emission makes the dominant contribution at these
wavelengths, expediting a stellar mass estimation: the median/quartiles are
logM_⋆/M_⊙=9.4_9.1^9.7. The number density of LRDs is
10^-4.0±0.1 Mpc^-3, accounting for 14±3
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
μm) spectral slope reveals significant amounts of dust (bolometric stellar
attenuation ∼3-4 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 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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