The angular correlation of quasars and Abell clusters

Studying the distribution of two large inhomogeneous quasar samples with respect to a statistical sample of Abell clusters, we find that optically selected high-redshift quasars strongly avoid foreground rich clusters. Radio-selected objects are found to be largely free from such bias. While foreground confusion may cause much of the avoidance, evidence from the radio sample suggests that an appreciable fraction of the effect is due to intervening absorption. We find >~ 25% deficit in the optical quasar counts extending typically 60' from the rich clusters. The absorption component can have substantial effects on observations of objects at cosmological distances.