2003MNRAS.343..639O

The redshifts of lens galaxies in known gravitational lens systems probe the volume distribution of the lensing mass. Following earlier work by Kochanek, we rederive the lens-redshift probability distribution, allowing for mass and number density evolution of the lensing galaxies, and apply this test to a much enlarged sample of lens systems. From a literature survey of all known lenses, we have selected an unbiased sample of 15 lenses with complete redshift information. For a flat universe and no lens evolution, we can only put an upper limit on the cosmological constant of Ω_Λ< 0.89 at the 95 per cent confidence limit (CL). Ω_Λ~ 0.7 and no evolution is consistent with the data. Allowing for evolution in an Ω_m= 0.3, Ω_Λ= 0.7 cosmology, we find that the best-fitting evolution in σ_*(i.e. the characteristic velocity dispersion in a Schechter-like function) of early-type galaxies, in the redshift range z ∼ 0 to 1, is d log [σ_*(z)]/dz =-0.10±0.06. This is consistent with no evolution and implies that, at 95 per cent CL, σ_*of early-type galaxies at z ∼ 1 was at least 63 per cent of its current value. Alternatively, if there is no mass evolution, a present-day value of σ_*> 175 km.s^–1 for elliptical galaxies is required (95 per cent CL).