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

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 done 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: (1) 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 (2) 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 +0.27 −0.14 (68%) for the unconstrained case or 0.40 +0.28 −0.16 (68%) 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 = px(pressure)/ρx(energy density) and the prior constraint w ≥ −1, we find that −1 ≤ w < −0.55 −0.11 (68%) for the unconstrained case or −1 ≤ w < −0.41 +0.28 −0.16 (68%) 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) 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 km s −1 (68%) for a ‘steep’ α = −1 or