Observational Properties of AGN Obscuration During the Peak of Accretion Growth
arxiv(2024)
摘要
We investigated the gas obscuration and host galaxy properties of active
galactic nuclei (AGN) during the peak of cosmic accretion growth of
supermassive black holes (SMBHs) at redshift 0.8-1.8 using X-ray detected AGN
with mid-infrared and far-infrared detection. The sample was classified as
type-1 and type-2 AGN using optical spectral and morphological classification
while the host galaxy properties were estimated with multiwavelength SED
fitting. For type-1 AGN, the black hole mass was determined from MgII emission
lines while the black hole mass of type-2 AGN was inferred from the host
galaxy's stellar mass. Based on the derived parameters, the distribution of the
sample in the absorption hydrogen column density (N_ H) vs. Eddington
ratio diagram is examined. Among the type-2 AGN, 28±5% are in the
forbidden zone, where the obscuration by dust torus cannot be maintained due to
radiation pressure on dusty material. The fraction is higher than that observed
in the local universe from the BAT AGN Spectroscopic Survey (BASS) data release
2 (11±3%). The higher fraction implies that the obscuration of the
majority of AGN is consistent with the radiation pressure regulated unified
model but with an increased incidence of interstellar matter (ISM) obscured
AGN. We discuss the possibility of dust-free absorption in type-1 AGN and heavy
ISM absorption in type-2 AGN. We also find no statistical difference in the
star-formation activity between type-1 and type-2 AGN which may suggest that
obscuration triggered by a gas-rich merging is not common among X-ray detected
AGN in this epoch.
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