An optical imaging survey for gravitational lenses and the discovery of a new lens candidate

We are conducting an optical imaging search for gravitational lenses. A sample of known quasars was selected on the basis of high redshifts and apparently large absolute luminosities; these selection criteria significantly enhance the probability that a given QSO is gravitationally magnified. So far, our search has yielded at least one new gravitational lens system, associated with the quasar UM 425 = 1120+019,,one binary quasar, PKS 1145-071, and several other promising candidates that still need spectroscopic confirmation. In addition, we found several cases of foreground galaxies within a few arcsec from the quasars, which should be useful for absorption line studies. The optical image of the UM 425 system consists of four or more components, at least two of which have identical spectra. There are many faint galaxies in the field, suggestive of a lensing cluster at a redshift of several tenths, and tentative evidence for a z ≅ 0.6 galaxy underlying the second-brightest quasar image. We conclude that the heuristically designed optical searches for gravitational lenses can successfully complement the radio-based surveys.