Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Takumi S. Tanaka, Takumi S. Tanaka, , ,
| Summary:
JWST has revealed a new high-redshift population called little red dots
(LRDs). Since LRDs may be in the early phase of black hole growth, identifying
them in the early universe is crucial for understanding the formation of the
first supermassive black holes. However, no robust LRD candidates have been
identified at $z>10$, because commonly-used NIRCam photometry covers
wavelengths up to $sim5,rm mu m$ and is insufficient to capture the
characteristic V-shaped spectral energy distributions (SEDs) of LRDs. In this
study, we present the first search for $zgtrsim10$ LRD candidates using both
NIRCam and MIRI imaging from COSMOS-Web, which provides the largest joint
NIRCam-MIRI coverage to date ($0.20,rm deg^2$). Taking advantage of
MIRI/F770W to remove contaminants, we identify one robust candidate, CW-LRD-z10
at $z_rm phot=10.5^+0.7_-0.6$ with $M_rm UV=-19.9^+0.1_-0.2,rm
mag$. CW-LRD-z10 exhibits a compact morphology, a distinct V-shaped SED, and a
non-detection in F115W, all consistent with being an LRD at $zsim10$. Based on
this discovery, we place the first constraint on the number density of LRDs at
$zsim10$ with $M_rm UVsim-20$ of $1.2^+2.7_-1.0times10^-6,rm
Mpc^-3,mag^-1$, suggesting that the fraction of LRDs among the overall
galaxy population increases with redshift, reaching $sim3%$ at $zsim10$.
Although deep spectroscopy is necessary to confirm the redshift and the nature
of CW-LRD-z10, our results imply that LRDs may be a common population at
$z>10$, playing a key role in the first supermassive black hole formation.
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