The cosmological evolution of quasar black hole masses

Virial black hole mass estimates are presented for 12698 quasars in the redshift interval 0.1 = 2000 km s-1) show a clear upper boundary at Lbol/LEdd~= 1, suggesting that the Eddington luminosity is still a relevant physical limit to the accretion rate of luminous broad-line quasars at z= 108 Msolar). By comparing the estimated number density of active black holes at z~= 2 with the local mass density of dormant black holes, we set lower limits on the quasar lifetimes and find that the majority of black holes with mass >=108.5 Msolar are in place by ~=2.