The fraction of obscured quasars

Junxian Wang

Center for AstrophysicsUniversity of Science and Technology of China

2006-10 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

LX ~ 1045 erg/s NH ~ 1024cm-2

narrow high-excitation lines Fe-line @ 6.4 keV

VLT-spectrum Chandra spectrum

Norman et al. 2002

1.4 keV = 6.4/(1+z)

• Hard X-ray surveys – better to select obscured quasars

• X-ray spectral fitting can give both intrinsic LX and absorption NH

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

14-195 keV selected

Markwardt et al. 2005

INTEGRAL IRS AGN sample20-100 keV selectedBassani et al. 2006

• Treister et al. 2004

• Eckart et al. 2006

• 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

14-195 keV selected

Markwardt et al. 2005

In the local universe

INTEGRAL IRS AGN sample20-100 keV selectedBassani 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-S107 4-7 keV selected redshift completeness 10

0%

CDF-N176 4-7 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!