The real-space clustering of luminous red galaxies around z < 0.6 quasars in the Sloan Digital Sky Survey

We measure the clustering of a sample of photometrically selected luminous red galaxies (LRGs) around a low-redshift (0.2 < z < 0.6) sample of quasars selected from the Sloan Digital Sky Survey Data Release 5. We make use of a new statistical estimator to obtain precise measurements of the LRG autocorrelations and constrain halo occupation distributions for them. These are used to generate mock catalogues which aid in interpreting our quasar-LRG cross-correlation measurements. The cross-correlation is well described by a power law with slope 1.8 +/- 0.1 and r(0) = 6 +/- 0.5 h(-1) Mpc, consistent with observed galaxy correlation functions. We find no evidence for 'excess' clustering on 0.1 Mpc scales and demonstrate that this is consistent with the results of Serber et al. and Strand, Brunner and Myers, when one accounts for several subtleties in the interpretation of their measurements. Combining the quasar-LRG cross-correlation with the LRG autocorrelations, we determine a large-scale quasar bias b(QSO) = 1.09 +/- 0.15 at a median redshift of 0.43, with no observed redshift or luminosity evolution. This corresponds to a mean halo mass << M >> similar to 10(12) h(-1) M-circle dot, Eddington ratios from 0.01 to 1 and lifetimes less than 10(7) yr. Using simple models of halo occupation, these correspond to a number density of quasar hosts greater than 10(-3) h(3) Mpc(-3) and stellar masses less than 10(11) h(-1) M-circle dot. The small-scale clustering signal can be interpreted with the aid of our mock LRG catalogues, and depends on the manner in which quasars inhabit haloes. We find that our small-scale measurements are inconsistent with quasar positions being randomly subsampled from halo centres above a mass threshold, requiring a satellite fraction > 25 per cent.