2003MNRAS.346..746C

Extensive analyses of statistical strong gravitational lensing are performed based on the final Cosmic Lens All-Sky Survey (CLASS) well-defined statistical sample of flat-spectrum radio sources and current estimates of galaxy luminosity functions per morphological type. The analyses are carried out under the assumption that galactic lenses are well-approximated by singular isothermal ellipsoids and early-type galaxies evolved passively since redshift z ∼ 1. Two goals of the analyses are: (i) to constrain cosmological parameters independently of other techniques (e.g. Type Ia supernovae magnitude-redshift relation, cosmic microwave background anisotropies, galaxy matter power spectra); and (ii) to constrain the characteristic line-of-sight velocity dispersion and the mean projected mass ellipticity for the early-type galaxy population. Depending on how the late-type galaxy population is treated (i.e. whether its characteristic velocity dispersion is constrained or not), we find for a flat universe with a classical cosmological constant that the matter fraction of the present critical density Ω_m0.31^+0.27_–0.14(68 per cent) for the unconstrained case or 0.40^+0.28_–0.16(68 per cent) for the constrained case, with an additional systematic uncertainty of ~0.11 arising from the present uncertainty in the distribution of CLASS sources in redshift and flux density. For a flat universe with a constant equation of state for dark energy w p_x(pressure)/ρ_x(energy density) and the prior constraint w ≥-1, we find that -1 ≤w < -0.55^+0.18_–0.11(68 per cent) for the unconstrained case or -1 ≤w < -0.41^+0.28_–0.16(68 per cent) for the constrained case, where w -1 corresponds to a classical cosmological constant. The determined value of the early-type characteristic velocity dispersion [σ^(e)_*] depends on the faint-end slope of the early-type luminosity function [α^(e) ] and the intrinsic shape distribution of galaxies; for equal frequencies of oblates and prolates, we find that σ^(e)_*(0.3 ≲z ≲ 1) 198⁺²²_–18km/s (68 per cent) for a `steep'α<sup>(e)</sup> -1 or σ<sup>(e)</sup><sub>*</sub>(0.3 ≲z ≲ 1) 181<sup>+18</sup> <sub>–15</sub>km/s (68 per cent) for a `shallow'α^(e) -0.54. Finally, from the relative frequencies of doubly imaged sources and quadruply imaged sources, we find that a mean projected mass ellipticity of early-type galaxies {bar}ε_{mass} = 0.42 with a 68 per cent lower limit of 0.28 assuming equal frequencies of oblates and prolates.