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Astron. Astrophys. 353, 440-446 (2000)

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The X-ray background and the evolution of AGN

F. Pompilio, F. La Franca and G. Matt

Dipartimento di Fisica, Università degli Studi "Roma Tre", Via della Vasca Navale 84, 00146 Roma, Italy

Received 30 July 1999 / Accepted 8 October 1999

Abstract

We discuss the constraints on the AGN evolution from the cosmic X-ray background and source counts. A synthesis model to fit the X-ray background is presented. The data used are a compilation from Gruber (1992), mainly based on HEAO-1 data. The spectrum of type 2 AGN has been modeled including Compton down-scattering within the absorbing material. We found an improvement when a dependence on redshift of the relative number of obscured sources is introduced. In particular, we found a decrease of the fraction of type 2 AGN at redshifts larger than [FORMULA]2.

However, only the soft X-ray counts are well reproduced, while the hard (5-10 keV) BeppoSAX/HELLAS source counts are underestimated by a factor of [FORMULA]1.5. A satisfactory global solution, including the good reproduction of the hard counts, is instead obtained if the XRB normalization, recently obtained from BeppoSAX/MECS measurements (about 30% higher than HEAO-1), is adopted.

Key words: cosmology: diffuse radiation – X-rays: general – galaxies: nuclei – galaxies: luminosity function, mass function

Send offprint requests to: F. Pompilio (pompilio@abell.fis.uniroma3.it)

This article contains no SIMBAD objects.

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999
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