The X-ray background and the evolution of AGN


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 ∼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 ∼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.

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@inproceedings{Pompilio1999TheXB, title={The X-ray background and the evolution of AGN}, author={Fulvio Pompilio}, year={1999} }