The luminosity function and clustering evolution of Quasars
  Recent results have questioned the description of the QSO luminosity function in terms of a pure luminosity evolution and call for a luminosity dependent luminosity evolution. Measurements of the QSO clustering amplitude and evolution allow further distinguishing among the various physical scenarios proposed to interpret the QSO phenomenon. The general properties of the QSO population would arise naturally if quasars are short-lived events connected to a characteristic halo mass $\sim 5 \cdot 10^{12}$ M$_\odot$. This is the typical mass of groups of galaxies in which the interactions triggering the QSO activity preferentially take place. 
S. Cristiani, F. La Franca, P. Andreani