We use 62 185 quasars from the Sloan Digital Sky Survey DR5 sample and standard virial mass scaling laws based on the widths of H?, Mg II and C IV lines and adjacent continuum luminosities to explore the maximum mass of quasars as a function of redshift, which we find to be sharp and evolving. This evolution is in the sense that high-mass black holes cease their luminous accretion at higher redshift than lower mass black holes. Further, turn-off for quasars at any given mass is more highly synchronized than would be expected given the dynamics of their host galaxies. We investigate potential signatures of the quasar turn-off mechanism, including a dearth of high-mass quasars at low Eddington ratio. These new results allow a closer examination of several common assumptions used in modelling quasar accretion and turn-off.
