Demography of high redshift AGN
  High redshift AGN holds the key to understand the early structure formation and to probe the Universe during its infancy. We review the latest searches for high-z AGN in the deepest X-ray field so far, the Chandra Deep Field South (CDFS) 4 Msecond exposure. We do not confirm the positive detection of a signal in the stacked Chandra images at the position of z~6 galaxies recently reported by Treister and collaborators. We present z>3 X-ray sources number counts in the 0.5-2 keV band obtained joining CDFS faint detections with Chandra-COSMOS and XMM-COSMOS detections. We use these number counts to make predictions for surveys with three mission concepts: Athena, WFXT and a Super-Chandra. 
Fabrizio Fiore (INAF-OAR), Simonetta Puccetti (ASI SDC), Smita Mathur   (Ohio State University)
astro-ph.CO