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E. Treister (Yale U. and U. de Chile), C.M. Urry (Yale U.), P. Lira (U. de Chile)
The AGN unification paradigm has been able to explain the observed properties of both obscured and unobscured AGN in the local Universe. However, whether this remains true at higher redshift is still unknown. Using a modified version of the AGN unification scheme, one in which the ratio of obscured-to-unobscured AGN changes with luminosity (more obscured AGN at lower luminosities) but does not evolve with redshift, we were able to explain the multiwavelength properties, ranging from infrared to X-rays, of the X-ray sources detected in the GOODS fields, which overlap with the deepest Chandra and XMM observations. This calculation assumes an average obscured-to-unobscured AGN ratio of 3:1, consistent with the observations of AGN in the local Universe. Allowing for an additional contribution from Compton-thick sources, we were able to explain the spectral shape and intensity of the X-ray background in the 1-100 keV range, where AGN emission is expected to dominate. The AGN contribution to the infrared background constrained from Spitzer observations of the GOODS fields is ~ 2\times lower than previously expected, about 3-6% in the 3-24 microns range. The possible dependence of the obscured to unobscured ratio with redshift is examined, and we outline a test of this dependence with a highly complete sample of AGN with measured redshifts using a combination of spectroscopic and reliable photometric redshifts.
We gratefully acknowledge support from Fundacion Andes, FONDAP Center of Astrophysics and Sigma Xi. This work was supported by NASA grants HST-GO-09425(.01-A,.13-A,.26-A) and HST-GO-09822.09-A.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.