First Results from the CLASS Gravitational Lens Survey: Two New Compact Radio Lenses with Arc-Second Separations

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Session 23 -- Gravitational Lensing
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

[23.06] First Results from the CLASS Gravitational Lens Survey: Two New Compact Radio Lenses with Arc-Second Separations

S.T. Myers, C.D. Fassnacht, S.G. Djorgovski, G. Neugebauer, T.J. Pearson, A.C. Readhead (Caltech), I.W.A. Browne, P.N. Wilkinson, S. Nair (NRAL Jodrell Bank), N. Jackson, I. Snellen, G. Miley (Leiden University), G. de Bruyn, R. Schilizzi (NFRA Dwingeloo)

The first phase of a large gravitational lens survey using the Very Large Array at a wavelength of 3.6 cm has been completed, yielding images for 3271 radio sources. The Cosmic Lens All-Sky Survey, or CLASS, is designed to locate gravitational lens systems consisting of multiply-imaged compact components with separations of $0.2$ -- 10 arc-seconds. Previous surveys indicate lensing-rates for samples of flat-spectrum radio sources of around $0.2$\%, therefore this phase of our survey is expected to yield 6 lenses. Lenses selected in this manner are likely to be suitable for time-delay measurements that can be used to measure the Hubble constant $H_0$, and over a large enough redshift range, $q_0$. So far, the survey has produced two un-ambiguous lenses: a quadruple-imaged object with maximum separation of 2.1 arcsec, and a doubly-imaged quasar with separation of 1.4 arcsec. Over a dozen candidates with simple double structure have also been extracted from the survey, and many more with complicated structure have been tagged for follow-up.

Optical images and spectra confirming the indentification of these candidates have been obtained. The lensed object in the double system has been identified as a quasar at redshift $z=1.6$. For the quad lens, a spectrum obtained with the Palomar 5-m telescope indicates a tentative redshift of $z\sim0.6$ for the lensing galaxy, and an infrared image from the NIRC on the Keck 10-m telescope has located the galaxy relative to the 4 lensed images. A preliminary lens model for the quad gives estimates for the time delays from around 10 days between the nearest components to around 200 days for images maximally separated on the time-delay surface. By the time of the meeting, radio variability data obtained at the Owens Valley Radio Observatory will be available to assess the viability of these lenses for time-delay measurements.

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