Title:

Emergence of Type-2 QSOs?



Masayuki Akiyama
Subaru Telescope


Abstract:

Recent results from deep X-ray surveys in the hard X-ray band above 2keV
suggest that relatively low-luminous AGNs, Seyfert galaxies, are a major
contributor to the cosmic X-ray background (CXB), and the contribution
from the luminous obscured AGNs, type-2 QSOs, is not significant. But,
still the number density of type-2 QSOs is not well constrained,
especially in the high redshift universe. In order to reveal  the number
density of luminous obscured AGN population, we are conducting hard
X-ray survey with XMM-Newton and deep optical imaging survey  with
Suprime-cam on Subaru covering ~1 sq. degree wide field, Subaru
XMM-Newton Deep Survey. The optical identification of the X-ray sources
indicates that large number of X-ray sources with large X-ray to optical
flux ratio, "optical faint", emerge at relatively shallow, 1x10^-14
erg/s/cm2, flux limit already and make significant contribution to the
CXB. Spectroscopic observations of the "optical faint" X-ray sources
revealed that many of them are obscured AGNs with X-ray luminosity
comparable to that of QSOs. Although spectroscopic identification of the
"optical faint" X-ray sources is not statistically complete, the results
can indicate we are sill missing a large population of type-2 QSOs.