Kavli Affiliate: John D. Silverman
| First 5 Authors: Yoshiki Matsuoka, Masafusa Onoue, Kazushi Iwasawa, Kentaro Aoki, Michael A. Strauss
| Summary:
The unprecedented sensitivity of the James Webb Space Telescope (JWST) has
uncovered a surprisingly abundant population of mildly obscured, low-luminosity
active galactic nuclei (AGNs) in the epoch of reionization (EoR). However, the
link between these objects and classical unobscured quasars remains a mystery.
Here we report the discovery of obscured quasars hosted by the most luminous
galaxies at $z > 6$, possibly bridging the gap between the two AGN populations.
The 13 objects presented here were originally selected from a rest-frame
ultraviolet (UV) imaging survey over $>$1000 deg$^2$, and were known to have
luminous ($>10^{43}$ erg s$^{-1}$) narrow Ly$alpha$ emission. With
JWST/NIRSpec follow-up observations, we found that nine of them exhibit a broad
component in H I Balmer lines and He I lines, but not in [O III] and other
forbidden lines. Mild dust obscuration ($0 < A_V < 3$) is inferred from the
Balmer decrements. The estimated intrinsic luminosities suggest that our broad
line (BL) objects are the long-sought UV-obscured counterparts of luminous
quasars in the EoR. They host supermassive black holes (SMBHs) with masses
$10^{7.8 – 9.1} M_odot$, undergoing sub-Eddington to Eddington accretion. Most
of the BL objects are spatially unresolved, and are close to "little red dots"
with their blue rest-UV and red rest-optical colors. We estimate the AGN number
density among similarly luminous Ly$alpha$ emitters to be larger than $2
times 10^{-8}$ Mpc$^{-3}$. This density is comparable to that of classical
quasars with similar continuum luminosities, suggesting that a substantial
fraction of active SMBHs are obscured in the EoR and have been overlooked in
past rest-UV surveys.
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