Quasar Clustering from SDSS DR7: Dependencies on FIRST Radio Magnitudes

Clustering is a measure of the dark matter environments in which galaxies are embedded. Quasars are a tracer of the state of active black holes throughout the Universe. The clustering of quasars as a function of their physical properties is thus a key measure in determining how black hole activity correlates with dark matter environment throughout cosmic history. Currently, the most abundant sample of quasars suitable for clustering measurements over most of cosmic history (and certainly over redshifts of about 0.8 < z < 2.2) is the uniform sample of quasars assembled as part of the seventh incarnation of the Sloan Digital Sky Survey (SDSS DR7). We study the clustering of quasars as a function of their physical properties using the ∼4000 deg^2 Sloan Digital Sky Survey Data Release Seven and a homogenous sample of 37,574 quasars. This work confirms the findings of Shen (2009) using DR5 and expands upon it using the larger DR7 catalog. We find that at lower redshifts quasar clustering depends weakly on luminosity. Cross-correlation of FIRST detected (radio-loud) quasars and autocorrelation of non-FIRST detected (radio-quiet) quasars indicates that radio-loud quasars cluster more strongly than do radio-quiet quasars. We agree with the conclusion that radio-loud quasars reside in more massive and denser environments, implying the possibility that it is the density of environment which determines a quasar's radio loudness, rather than a duty cycle.