Abstract
Accretion is the dominant mechanism governing the growth of massive black holes in galaxy centers. Surveys at X-ray wavelengths trace the accretion history in the Universe and reveal that most of it occurs in obscured objects. In this paper we present some results from the XMM-Newton Medium Sensitivity survey (XMS), which investigates the source population that produces about the brightest half of the X-ray background below 10 keV. We emphasize the role of large aperture telescopes, such as GTC, in unveiling the black hole growth in obscured objects.
