The Flat‐Spectrum Radio Luminosity Function, Gravitational Lensing, Galaxy Ellipticities, and Cosmology

The number of lenses found in the JVAS survey of flat-spectrum radio sourcesfor gravitational lenses is consistent with statistical models of opticalsurveys for lensed quasars. The 90% confidence limit on Omega_0 in flatcosmological models (Omega_0+lambda_0=1) is approximately 0.15 < Omega_0 < 2.Depending on the RLF model, we predict 2.4 to 3.6 lenses in the JVAS survey andin the first part of the fainter CLASS survey, and 0.3 to 0.6 lenses in thebrighter PHFS survey for an Omega_0=1 model. The uncertainties are due to thesmall numbers of lenses (there are only 4 compact JVAS lenses) and theuncertainties in the radio luminosity function (RLF) caused by the lack ofinformation on the redshift distribution of 10-300 mJy radio sources. If weforce the models to produce the observed number of JVAS lenses, the meanredshift of a 50 mJy source varies from z_s=0.4 for Omega_0=0, to 1.9 forOmega_0=1, to almost 4.0 for Omega_0=2 when Omega_0+lambda_0=1. The sourcefluxes and redshifts of the lenses in the JVAS and CLASS surveys are consistentwith the statistical models. The numbers of four-image lenses found in the JVASsurvey and in surveys for lensed quasars are mutually consistent, but slightlylarger than expected for models using the observed axis ratios of E and S0galaxies. The best fits to the lens data require a projected axis ratio ofb/a=0.50 with a 90% confidence range of 0.25 < b/a < 0.65.Comment: 37 pages, 12 PostScript figures, ApJ in pres