Redshifts of the Gravitational Lenses B1422+231 and PG1115+080

Abstract

B1422+231 and PG1115+080 are gravitational lens systems producing quadruple QSO images where there is real promise that time delays can constrain the Hubble constant. In addition, the lensing galaxies are both part of groups which can play an important role in modelling the lens potential. This article reports redshifts for the lensing galaxies and three neighboring galaxies in each of the two systems. B1422+231 consists of a group at z=0.339 with a dispersion of 733 km/s, and PG1115+080 is a group at z=0.311 with a dispersion of 326 km/s. One of the neighboring galaxies in the B1422+231 system turned out to be an emission line galaxy at z=0.536, suggesting that QSO light passing through B1422+231 may have been subjected to lensing by a cluster at this more distant redshift. The velocity dispersion of the lensing galaxy in PG1115+080 is determined to be 281+/-25 km/s (1" square aperture), which is surprisingly large given the image splittings of 1.2" in that system.