Detection of statistical gravitational lensing by foreground mass distributions

Physical associations between galaxies and quasars are known to exist at low redshift, but here evidence is presented for the detection of distant quasars associated with foreground galaxies. The quasars which are juxtaposed with faint galaxies are compared with a control sample of quasars selected using identical techniques. We find clear statistical evidence for a greater number of quasar-galaxy juxtapositions than would be expected from random alignments. A possible explanation is gravitational lensing of the background quasars by matter associated with the foreground galaxies. From the enhancement of the quasar surface density in the vicinity of the galaxies we are able to draw some general conclusions about the distribution of the lensing matter. (author)