Invited highlight talk at the 7th INTEGRAL Workshop, September 8-11, 2008. Copenhagen, Denmark.
astro-ph/0902.3033

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Abstract. The Cosmic X-ray background carries the information of cosmic accretion onto super-massive black holes. The intensity at its peak can be used to constrain the integrated space density of highly obscured AGNs. Determining the shape and intensity of the Cosmic X-ray background radiation represents, however, a first step towards the understanding of the population of Compton-thick AGNs. The study of AGNs in the local and more distant Universe allows to understand the whole picture. In this talk, I will review the current understanding of generation of the Cosmic X-ray background at its peak. I will focus on the recent measurements of the Cosmic X-ray background and I will discuss the recent advancements in the understanding of AGNs in both the local and more distant Universe. Finally, I will also discuss open issues and future prospects.

Keywords Astrophysics - Cosmology and Extragalactic Astrophysics

Table of Contents

• INTRODUCTION
• History of the Cosmic X-ray background
• Constraints from the Cosmic X-ray background
• ADVANCES IN THE MEASUREMENT OF THE COSMIC X-RAY BACKGROUND
• HARD X-RAY SURVEYS
• The role of absorption
• Compton-thick AGNs in the local Universe
• Compton-thick AGNs in the high-z Universe
• REFLECTION AND CUT-OFF PROPERTIES OF AGNs
• UNVEILING THE HARD X-RAY SKY: THE SIX SURVEY
• CONCLUSIONS
• REFERENCES