Data Centre for Astrophysics
Astronomy Department of the University of Geneva
ISDC Seminar

Wednesday, 21 September 2005 at 14:00

Ezequiel Treister
University of Chile / Yale

AGN Unification and the X-ray Background

Abstract. The simplest AGN unification paradigm, one in which the ratio of obscured to unobscured AGN is constant with redshift and luminosity, can successfully explain the multiwavelength number counts of the X-ray sources detected in the GOODS fields, that include the deepest Chandra/XMM observations. Assuming a constant ratio of obscured to unobscured AGN of 3:1, including Compton-thick sources, we were able to explain the spectral shape and normalization of the X-ray background. Based on new observations that suggest that the relative number of obscured AGN can decrease with luminosity, we introduce a luminosity dependence in our unification model. This new model can still explain the properties of sources in the GOODS fields and is consistent with the X-ray background observations. The possible dependence of the obscured to unobscured ratio with redshift and ways to test this dependence will be discussed.

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