ar X iv : a st ro - p h / 97 07 03 2 v 1 2 J ul 1 99 7 Limits on Cosmological Models From Radio - Selected Gravitational Lenses

We are conducting a redshift survey of 177 flat-spectrum radio sources in 3 samples covering the 5 GHz flux ranges 50–100, 100–200 and 200–250 mJy. So far, we have measured 124 redshifts with completenesses of 80%, 68% and 58% for the bright, intermediate, and faint flux ranges. Using the newly determined redshift distribution we can derive cosmological limits from the statistics of the 6 gravitational lenses in the JVAS sample of 2500 flat-spectrum radio sources brighter than 200 mJy at 5 GHz. For flat cosmological models with a cosmological constant, the limit using only radio data is Ω 0 > 0.27 at 2−σ (0.47 < Ω 0 < 1.38 at 1−σ). The limits are statistically consistent with those for lensed quasars, and the combined radio + optical sample requires Ω 0 > 0.38 at 2−σ (0.64 < Ω 0 < 1.66 at 1−σ) for our most conservative redshift completeness model and assuming that there are no quasar lenses produced by spiral galaxies. Our best fit model improves by approximately 1−σ if extinction in the early-type galaxies makes the lensed quasars fainter by ∆m = 0.58 ± 0.45 mag, but we still find a limit of Ω 0 > 0.26 at 2−σ in flat cosmologies. The increasing fraction of radio galaxies as compared to quasars at fainter radio fluxes (rising from ∼10% at 1 Jy to ∼50% at 0.1 Jy) explains why lensed optical emission is common for radio lenses and partly explains the red color of radio-selected lenses. 1 Observations reported here were made with the Multiple Mirror Telescope Observatory, which is operated jointly by the University of Arizona and the Smithsonian Institution 2 Observations reported here were obtained, in part, at MDM Observatory,