The Evolution and Luminosity Function of Quasars

Abstract

I report results from analysis of data from several quasar samples (Durham/AAT, LBQS, HBQS and EQS) on the density and the luminosity evolution of quasars. We have used new statistical methods whereby we combine these different samples with varying selection criteria and multiple truncations. With these methods the luminosity evolution can be found through an investigation of the correlation of the bivariate distribution of luminosities and redshifts. Of the two most commonly used models for luminosity evolution, L = ekt(z) and L = (1 + z)k', we find that the second form, with k' = 2.58 (one σ range [2.14,2.91]), gives a better description of the data at all luminosities. Using this form of luminosity evolution we determine a global luminosity function and the evolution of the co-moving density for the two classes of cosmological models. We find a gradual increase of the co-moving density up to z ˜ 2, at which point the density peaks and begins to decrease rapidly. This is in agreement with results from high redshift surveys and in disagreement with the pure luminosity evolution (i.e. constant co-moving density) model. We find that the local luminosity function exhibits the usual double power law behavior. The luminosity density is found to increase rapidly at low redshift and to reach a peak at around z ≍ 2. This result is compared with those from high redshift surveys and with the evolution of the star formation rate.