1. The fraction of obscured quasars Junxian Wang Center for Astrophysics University 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

4. 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)

5. CDFS 202: a classic type 2 quasar L X ~ 10 45 erg/s N H ~ 10 24 cm -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)

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

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

8. Ueda et al. 2003

10. Receding torus? Seyfert QSO  h r 

11. Steffen et al. 2003

12. SWIFT/BAT AGN sample 14-195 keV selected Markwardt et al. 2005

13. INTEGRAL IRS AGN sample 20-100 keV selected Bassani et al. 2006

14. Simpson 2005

15. Zhang S. N. 2005

16. 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

17. SWIFT/BAT AGN sample 14-195 keV selected Markwardt et al. 2005 In the local universe

18. INTEGRAL IRS AGN sample 20-100 keV selected Bassani et al. 2006

19. Wang & Jiang 2006

20. Chandra Deep Fields

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

24. Obscured quasars

26. CDF-S 107 4-7 keV selected redshift completeness 100%

27. CDF-N 176 4-7 keV selected, redshift completeness 72%

28. due to redshift incompleteness?

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

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

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

33. Thank you!