It is well established that the population of Active Galactic Nuclei (AGN), which are powered by accretion on supermassive black holes (SBH) at the centres of galaxies, has declined dramatically in the last 7 Gyrs of cosmic time (from z=1 to z=0). Elucidating the physical mechanism responsible for this rapid evolution remains a challenge for astronomy, despite over 35 years of investigations. It is the ambitious but realistic goal of this proposal to address this long-standing problem. A recent development that promises a breakthrough in the field has been the realisation that in order to understand active SBHs we need to study them in relation to their host galaxies. At high redshift (z~1) for example, there is currently a wealth of information on the nature of AGN hosts that provide important clues on the physical conditions under which accretion on SBHs occurs. Such studies have to be performed over a wide redshift baseline however, if we hope to get a handle on the physics behind AGN evolution. Unfortunately, although a huge amount of resources has been devoted to observations of the deep Universe, there is currently no systematic effort to complement them at low redshift. This proposal will bridge this gap by compiling the largest sample of X-ray selected AGN at z~0.1 to study the properties of their hosts, including their (i) star-formation history, (ii) stellar mass and (iii) large scale environment. A unique feature of the proposed program is that the AGN selection is almost identical to high redshift surveys, thereby allowing direct comparison of the samples. The proposed survey at z~0.1 will be combined with similar programs at z~1 to perform, for the first time, redshift dependent studies of the conditions under which AGN occur, thereby placing tight constraints on the physics that govern the accretion history of the Universe.
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