Large‐Scale QSO‐Galaxy Correlations for Radio‐loud and Optically Selected QSO Samples

We have studied the distribution of $B_J<20.5$ galaxies from the ROE/NRLCOSMOS/UKST catalogue around two samples of $z>0.3$ QSOs with similar redshiftdistributions. The first sample is formed by 144 radio-loud QSOs from theParkes Catalogue, and the other contains 167 optically selected QSOs extractedfrom the Large Bright Quasar Survey. It is found that there is a $\approx99.0%$ significance level excess of COSMOS/UKST galaxies around the PKS QSOs,whereas there is a marginal defect of galaxies around the LBQS QSOs. When thedistribution of galaxies around both samples is compared, we found that thereis an overdensity of galaxies around the PKS sample with respect to the LBQSsample anticorrelated with the distance from the QSOs at a $99.7%$ significancelevel. Although this result apparently agrees with the predictions of thedouble magnification bias, it is difficult to explain by gravitational lensingeffects alone; dust in the foreground galaxies and selection effects in thedetection of LBQS QSOs should be taken into account. It has been establishedthat the lines of sight to PKS flat-spectrum QSOs go through significativelyhigher foreground galaxy densities than the directions to LBQS quasars, whatmay be partially related with the reported reddening of PKS QSOs.Comment: 18 pages, 8 figures, AASTeX, accepted for publication in Ap