EVOLUTION OF THE LUMINOSITY FUNCTION OF QUASAR ACCRETION DISKS

The shape and evolution of the luminosity function of quasars is linked to their physical evolution in the context of the accretion-disk model. Accretion disk luminosities are calculated for a grid of black hole masses and accretion rates. It is shown that as the black hole mass increases with time, the monochromatic luminosity at a given frequency first increases then decreases rapidly as the Wien cutoff crosses this frequency. At any epoch there exists a well-defined upper limit on the monochromatic luminosity. This limit constrains the evolution of quasar luminosities for a wide range of quasar source function and accretion scenarios and determines the evolution of the quasar luminosity function. Pure luminosity evolution (PLE) is shown to be inconsistent with the accretion disk model and pure accretion evolution (PAE) is introduced to explain the shape of the luminosity function and its evolution with redshift. In particular, the characteristic break in the luminosity function slope is associated with the maximum luminosity envelope, and the luminosity evolution is shown to be a direct result of the accretion time scale. Possible modifications to this simple scenario and their consequences are discussed.