The fraction of obscured quasars Junxian Wang Center for Astrophysics University of Science and Technology of China Xi’an, China Collaborated with P. Jiang, Z. Y. Zheng (USTC) and the Chandra Deep Field South team

obscured quasar? Required by the AGN unified model Required by the X-ray background model The population of obscured quasars -- dominate the black hole growth??? Difficult (rare, hard to select and measure the intrinsic luminosity)

CDFS 202: a classic type 2 quasar L X ~ erg/s N H ~ cm -2 narrow high-excitation lines 6.4 keV VLT-spectrum Chandra spectrum Norman et al keV = 6.4/(1+z)

Hard X-ray surveys – better to select obscured quasars X-ray spectral fitting can give both intrinsic L X and absorption N H

Absorption vs luminosity QSO2s From Mainieri et al. (2002) CDFS XMM Lockman Hole

Ueda et al. 2003

Receding torus? Seyfert QSO  h r 

Steffen et al. 2003

SWIFT/BAT AGN sample keV selected Markwardt et al. 2005

INTEGRAL IRS AGN sample keV selected Bassani et al. 2006

Simpson 2005

Zhang S. N. 2005

Treister et al Eckart et al Dwelly et al. 2005, Dwelly & Page 2006 Martinez-Sansigre et al. 2005, 2006 (a talk this Saturday) Zhang 2005 Contrary results

SWIFT/BAT AGN sample keV selected Markwardt et al In the local universe

INTEGRAL IRS AGN sample keV selected Bassani et al. 2006

Wang & Jiang 2006

Chandra Deep Fields

We choose 4 -7 keV selected samples in Chandra Deep Fields to study the population of obscured quasars Why?

Obscured quasars

CDF-S keV selected redshift completeness 100%

CDF-N keV selected, redshift completeness 72%

due to redshift incompleteness?

Conclusions More than half of the 4-7 keV selected quasars in Chandra Deep Fields are obscured Wang et al 2006 ApJ submitted

Conclusions Redshift incomplete samples in deep fields can produce spurious declination in the fraction of obscured AGN with luminosity

Conclusions The anti-correlation between absorption and luminosity in the local universe is mainly due to the Compton-thick and radio loud sources

Thank you!