A SEARCH FOR ASSOCIATIONS OF DISTANT RADIO-BRIGHT QUASARS WITH ABELL CLUSTERS - AN EFFECT OF GRAVITATIONAL AMPLIFICATION BIAS

Theory predicts that the effect of gravitational lensing by the matter associated with clusters of galaxies can magnify background sources, leading to an enhancement of source number density around foreground c lusters of galaxies. We conduct a search for associations of distant r adio-bright quasars with Abell clusters, using the 1-Jy and 2-Jy all-s ky catalogues. The statistics are very poor for the 1-Jy sample, which shows no correlations between the distant radio quasars and the foreg round Abell clusters above the 1 sigma level. An apparent association (> 1sigma) of the 2-Jy radio sources with the foreground Abell cluster s, however, has been detected on a scale of approximately 20 arcmin. W e point out that this enhancement is unlikely to be explicable by the statistical gravitational lensing hypothesis utilizing the matter asso ciated with a population of isolated clusters unless (i) their velocit y dispersion is a few times larger than the presently adopted value, a nd/or (ii) the intrinsic counts of the radio-bright sources with flux have a steeper slope than do the presently observed relations. These r esults indicate that (1) the observed associations, if real, may be th e integrated result of all the matter along the lines of sight to the distant quasars, namely the weak lensing effect of clusters of galaxie s that trace large-scale structures of the Universe, and/or (2) the nu mber counts of the radio-bright sources have been seriously contaminat ed by lensing.