| Abstract: |
Understanding the influence of black hole growth on star formation and galaxy evolution over cosmic time scales requires a census of the AGN population, in particular in respect to their black hole masses and accretion rates. We present such a census of the active black hole population from z=0 to z=2, with an emphasis on 1 < z < 2, by studying the bivariate distribution function of black hole mass and Eddington ratio. This allows to clearly disentangle the AGN downsizing phenomenon, present in the AGN luminosity function (AGN LF), into its physical processes of black hole mass downsizing and accretion rate evolution. Compared to z = 0 we find a distinct change in the shape of the black hole mass and Eddington ratio distribution function, consistent with downsizing in black hole mass. The active fraction or duty cycle of type-1 AGN at z~1.5 is almost flat as a function of black hole mass, while it shows a strong decrease with increasing mass at z = 0. We are witnessing a phase of intense black hole growth, which is largely driven by the onset of AGN activity in massive SMBHs towards z = 2. We discuss the implications of these observational constraints for theoretical models of galaxy evolution and black hole growth. |
