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 7 out of 11 objects with
narrow Ly$alpha$ 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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