Quasar clustering from SDSS DR5: Dependences on physical properties

Using a homogenous sample of 38,208 quasars with a sky coverage of 4000 deg² drawn from the Sloan Digital Sky Survey Data Release Five quasar catalog, we study the dependence of quasar clustering on luminosity, virial black hole (BH) mass, quasar color, and radio loudness. At z < 2.5, quasar clustering depends weakly on luminosity and virial BH mass, with typical uncertainty levels 10% for the measured correlation lengths. These weak dependences are consistent with models in which substantial scatter between quasar luminosity, virial BH mass, and the host dark matter halo mass has diluted any clustering difference, where halo mass is assumed to be the relevant quantity that best correlates with clustering strength. However, the most luminous and most massive quasars are more strongly clustered (at the 2σ level) than the remainder of the sample, which we attribute to the rapid increase of the bias factor at the high-mass end of host halos. We do not observe a strong dependence of clustering strength on quasar colors within our sample. On the other hand, radio-loud quasars are more strongly clustered than are radio-quiet quasars matched in redshift and optical luminosity (or virial BH mass), consistent with local observations of radio galaxies and radio-loud type 2 active galactic nuclei. Thus, radio-loud quasars reside in more massive and denser environments in the biased halo clustering picture. Using the Sheth etal. (2001) formula for the linear halo bias, the estimated host halo mass for radio-loud quasars is 10¹³ h ^-1 M _⊙, compared to 2 × 10¹² h ^-1 M _⊙ for radio-quiet quasar hosts at z 1.5.