The new two-image gravitational lens system CLASS B2319+051

Abstract

We report the discovery of a new two-image gravitational lens system from the Cosmic Lens All-Sky Survey, CLASS B2319+051. Radio imaging with the Very Large Array (VLA) and Multi-Element Radio-Linked Interferometer Network (MERLIN) shows two compact components with a flux density ratio of 5:1, separated by 1.36 arcsec. Observations with the Very Long Baseline Array (VLBA) resolve each of the radio components into a pair of parity-reversed subcomponents. Hubble Space Telescope (HST) observations with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) show a bright elliptical galaxy (G1) coincident with the radio position, and a second irregular galaxy (G2) 3.4 arcsec to the northwest. Previous spectroscopic studies have indicated that these galaxies are at different redshifts: z(G1) = 0.624, z(G2) = 0.588. Infrared counterparts to the lensed radio components are not detected in the NICMOS image, and the source redshift has not yet been determined. Preliminary mass modeling based on the VLBA subcomponent data indicates that the lensing potential includes a strong external shear contribution. A VLA monitoring program is currently being undertaken to measure the differential time delay.