Quasar Clustering: Evidence for an Increase with Redshift and Implications for the Nature of Active Galactic Nuclei

The evolution of quasar clustering is investigated with a new sample of 388 quasars with 0.3 0.0 are excluded at a 0.3% probability level, compared with ~ 0.8 found for galaxies. The observed clustering properties appear qualitatively consistent with a scenario of Ω = 1 cold dark matter in which (1) the difference between the quasar and the galaxy clustering can be explained as a difference in the effective bias and redshift distributions and (2) the quasars, with a lifetime of t ~ 108 yr, sparsely sample halos of mass greater than Mmin ~ 1012-1013 h-1 M☉. We also discuss the possibility that the observed change in the quasar clustering is due to an increase in the fraction of early-type galaxies as quasar hosts at high z.