Models of the quasar population. I - A new luminosity function

Abstract

A new functional form for the quasar luminosity function is tested using recent observational results for both bright and faint quasar count and redshift distributions. The form is of a fairly general type based on three free parameters and allows for quasars to undergo a combination of luminosity evolution and luminosity-dependent density evolution; an advantage to this approach is that it does not constrain quasars to follow a single type of evolution. Models of pure luminosity evolution or luminosity-dependent density evolution can be constructed, but the apparent magnitude distribution of observed quasars is best fitted by a combination model. The combination model also gives the correct redshift distribution for quasars with redshifts less than three and predicts that quasars brighter than B = 22 provide a 2-10 keV X-ray flux that is equal to 32 percent of the observed X-ray background. However, the model is flawed in that it predicts more high-redshift quasars than are observed.