Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Kohei Inayoshi, Shigeo Kimura, Hirofumi Noda, ,
| Summary:
The James Webb Space Telescope (JWST) observations enable the exploration of
active galactic nuclei (AGNs) with broad-line emission in the early universe.
Despite their clear radiative and morphological signatures of AGNs in
rest-frame optical bands, complementary evidence of AGN activity — such as
X-ray emission and UV/optical variability — remains rarely detected. The
weakness of X-rays and variability in these broad-line emitters challenges the
conventional AGN paradigm, indicating that the accretion processes or
environments around the central black holes (BHs) differ from those of
low-redshift counterparts. In this work, we study the radiation spectra of
super-Eddington accretion disks enveloped by high-density coronae.
Radiation-driven outflows from the disk transport mass to the poles, resulting
in moderately optically-thick, warm coronae formed through effective inverse
Comptonization. This mechanism leads to softer X-ray spectra and larger
bolometric correction factors for X-rays compared to typical AGNs, while being
consistent with those of JWST AGNs and low-redshift super-Eddington accreting
AGNs. In this scenario, UV/optical variability is suppressed due to photon
trapping within super-Eddington disks, while X-ray emissions remain weak yet
exhibit significant relative variability. These characteristics are
particularly evident in high-redshift AGNs powered by lower-mass BHs with
$lesssim 10^{7-8}~M_odot$, which undergo rapid mass accretion following
overmassive evolutionary tracks relative to the BH-to-stellar mass correlation
in the local universe.
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