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 Royal Observatory Edinburgh/Naval Research Laboratory COSMOS/UKST catalog a round two samples of z > 0.3 QSOs with similar redshift distributions. The first sample is formed by 144 radio-loud QSOs from the Parkes cat alog (PKS), and the other contains 167 optically selected QSOs extract ed from the Large Bright Quasar Survey (LBQS). It is found that there is a approximate to 99.0% significance level excess of COSMOS/UKST gal axies around the PKS QSOs, whereas there is a marginal defect of galax ies around the LBQS QSOs. When the distribution of galaxies around bot h samples is compared, we find that there is an overdensity of galaxie s around the PKS sample with respect to the LBQS sample anticorrelated with the distance from the QSOs at a 99.7% significance level. Althou gh this result apparently agrees with the predictions of the multiple magnification bias, it is difficult to explain by gravitational lensin g effects alone; dust in the foreground galaxies and selection effects in the detection of LBQS QSOs should be taken into account. It has be en established that the lines of sight to PKS flat-spectrum QSOs go th rough significantly higher foreground galaxy densities than the direct ions to LBQS quasars, what may be partially related to the reported re ddening of PKS QSOs.