Stacking photons in deep and large X-ray surveys
Marcella Brusa (Max Planck Institut fuer Extraterrestrische Physik (MPE - Garching), UMBC)
Using the stacking technique, it is possible to study, at least in a statistical sense, the X-ray properties of sources individually undetected even in the deepest observations and down to extremely faint fluxes. Given the very low background of the Chandra satellite, such a technique has been routinely adopted in Chandra works since the beginning of the mission, and successfully used in a variety of studies. Here we present an overview of a few selected results, focused on: 1) the average X-ray properties of the sources responsible for the XRB; 2) the detection of a sizable poulation of Compton Thick AGN at z 2; and 3) the study of the intensity and profile of the 6.4 keV iron line and its evolution with redshift. We also briefly outline the perspectives for these studies for the Chandra mission, and for other present and future X-ray facilities, in the framework of the deepest (Chandra Deep Fields) and largest (e.g. COSMOS) surveys.