A search for gravitational lenses and quasar pairs and the discovery of a new multiple QSO system

Abstract

We are conducting an optical imaging survey for lensed quasars, with a spectroscopic follow-up for the promising cases. A sample of known QSOs has been selected on the basis of apparently large absolute luminosities and high redshifts. So far, this survey has yielded one close pair of possibly interacting quasars, PKS 1145-071, one very probable gravitational lens, UM 425, several other promising lens candidates, and several cases of foreground or associated galaxies within a few arcsec from the quasars. Recently, we have discovered another interesting system, PHL 1222, probably a close physical pair of QSOs with similar redshifts, z≃1.91, and separated by 3.3 arcsec. At least three other foreground faint objects (R~24 mag) are observed inside a circle of 7 arcsec around the quasar. In PHL 1222 we may be witnessing a triggering event responsible for the nonthermal activity in both objects, i.e., the birth of a quasar pair at a redshift where the comoving density of quasars was close to its maximum.