The cosmic X-ray background: news on the Compton-thick AGN population
R. Gilli, A. Comastri, G. Hasinger
The combination of deep and wide field X-ray surveys performed with Chandra and XMM is providing a major advance in the understanding of the cosmological evolution of X-ray selected AGN. A new, up-to-date modeling of the X-ray background will be presented and discussed, with particular emphasis on still controversial issues such as the variation of the nuclear obscuration with source redshift and luminosity and the space density of Compton-thick sources.