The Cosmic Lens All-Sky Survey: Statistical strong lensing, cosmological parameters, and global properties of galaxy populations

Abstract

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 la 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 Ωm = 0.31 -0.14+0.27 (68 per cent) for the unconstrained case or 0.40-0.16+0.28 (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)/ ρx(energy density) and the prior constraint ≥ -1, we find that -1 ≤ w < -0.55-0.11+0.18 (68 per cent) for the unconstrained case or -1 ≤ w < -0.41-0.16+0.28 (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) = 198-18-22 km s-1 (68 per cent) for a 'steep' α (e) = -1 or σ*(e) (0.3 ≲ z ≲ 1) = 181-15+18 km s-1 (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 ε̄mass = 0-42 with a 68 per cent lower limit of 0.28 assuming equal frequencies of oblates and prolates.