Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Takumi S. Tanaka, John D. Silverman, Kazuhiro Shimasaku, Junya Arita, Hollis B. Akins
| Summary:
“Little Red Dots” (LRDs) are an abundant high-redshift population newly
discovered by the James Webb Space Telescope (JWST). They are characterized by
a red color in the rest-frame optical band, compact morphology, and broad
Balmer emission lines (${rm FWHM} gtrsim 1000~{rm km,s^{-1}}$) that suggest
an AGN nature. Using a method of pixel-by-pixel color selection and relaxing
the compactness criteria, we identify three of the first dual LRD candidates in
the COSMOS-Web survey with projected separations of
$0.!!^{primeprime}2-0.!!^{primeprime}4$ (1-2 pkpc at their photometric
redshifts). A comparison between existing LRD samples and mock data reveals
that the projected separations of these dual LRD candidates are unlikely to
result from chance projections of objects at different redshifts. In one case
(CW-B5-15958), the dual LRD includes two bright sources ($m_{rm F444W}=24.3$
and $24.8$) with characteristic V-shape spectral energy distribution (SEDs) and
photometric redshifts consistent with each other. We find that CW-B5-15958 has
a faint off-centered component and a companion galaxy. In the other two dual
systems, the brighter LRD exhibits a V-shape SED, while the fainter LRD
($m_{rm F444W}gtrsim26$) is undetected in both F115W and F150W. These
discoveries suggest that the angular auto-correlation function (ACF) of LRDs
exhibits a significant excess ($sim3times10^2$ times) on sub-arcsec
(kilo-parsec) separations compared to the extrapolation of a power-law ACF of
JWST-found AGNs measured over $10^{primeprime}-100^{primeprime}$. Follow-up
spectroscopic confirmation of their redshifts and the construction of a larger
sample are essential to advance our understanding of the evolution of
supermassive black holes and the importance of mergers in the early universe.
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