A HIGH-RESOLUTION GRAVITATIONAL LENS SURVEY

We have conducted a search for gravitationally lensed QSOs using the Canada-France-Hawaii telescope under very good seeing conditions (median 0.70'' full width at half maximum). A sample of 104 bright (V < 18.5 mag), high redshift (z greater-than-or-equal-to 1. 5) QSOs was chosen to maximize the probability of lensing. At least two r band CCD exposures were obtained of almost every QSO, with a subsequent exposure in B if there was evidence of a close neighbor. Each QSO was carefully examined by visually comparing its contour plot with that of at least one reference star from the same field. Simulations were used to determine upper limits of detectability of a close companion. Although we rediscovered some previously known systems, no definitive new cases of gravitational lensing were found. Specifically, aside from one possible exception, there are no secondary components down to 2 mag fainter than the primary at separations greater than or similar to 0.60'', and none down to 0.5 mag fainter than the primary at separations greater than or similar to 0.4''. These results are consistent with recent theoretical calculations of the expected distribution of separations for gravitationally lensed QSOs.