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 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 m = 0.31 + 0 . 2 7 -0.14 (68 per cent) for the unconstrained case or 0.40 + 0 . 2 8 -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 ω ≥ -1, we find that -1 ≤ ω < -0.55 + 0 . 1 8 -0.11 (68 per cent) for the unconstrained case or -1 ≤ w < -0.41 + 0 . 2 8 -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 ( 3 ) ] and the intrinsic shape distribution of galaxies; for equal frequencies of oblates and prolates, we find that σ ( e ) *(0.3 ≤ z ≤ 1) = 198 + 2 2 -18 km s - 1 (68 per cent) for a 'steep' α ( 3 ) = -1 or σ ( e ) *(0.3 ≤ z ≤ 1) = 181 + 1 8 -15 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 ∈ m a s s = 0.42 with a 68 per cent lower limit of 0.28 assuming equal frequencies of oblates and prolates.