The X-Ray Background and the Space Distribution of QSOs

Abstract.

In this contribution I give a short review of the X-ray background measurements and the understanding of its origin in the light of the 1989 interpretation of G. Setti and L. Woltjer in terms of accretion power of obscured AGN. According to this model, which has been refined and improved in the last decade through deep imaging observations of all X-ray satellites, the X-ray background is mainly the radiation emitted during the buildup-phase of the supermassive black holes which we see in most larger normal galaxies today. The majority of this emission is, however, absorbed by thick gas and dust clouds surrounding the growing black holes.