Quasar-galaxy correlations: A search for amplification bias

Weak gravitational lensing by clusters and superclusters can change our per ception of the distribution of bright background quasars through a phenomen on known as amplification bias. It has been suggested that this lensing wil l lead to an association of moderate redshift quasars (z similar to 1.0-2.0 ) and foreground galaxies (z similar to 0.2-0.3). We report on the analysis of a homogeneous sample of 32 CCD fields centered on quasars that are brig ht both at radio (S-5 GHz > 1 Jy) and optical (V < 18.5) wavelengths, along with 11 control fields. These 69' x 69' fields are a small subset of our l arger survey of the fields around approximately 100 quasars and approximate ly 20 control fields. The quasars presented here are chosen to have the hig hest potential for evidence of this weak lensing effect. We find no evidenc e for the presence of rich galaxy clusters (Abell richness class = 1) in th e foreground of these fields. However, using a Spearman rank-order correlat ion test, we have detected a correlation between galaxy number density and angular distance from bright quasars on scales less than 30' with a signifi cance of 99%. This angular correlation is consistent with the recent semian alytic models of Dolag & Bartelmann that incorporate nonlinear evolution of matter.