Estimating cosmological parameters from future gravitational lens surveys

TL;DR

This paper explores how future gravitational lens surveys can significantly improve constraints on cosmological parameters like Omega_m, Omega_Lambda, and H_0 by analyzing large samples of time delay lenses, assuming certain galaxy and cosmology models.

Contribution

It demonstrates that large samples of time delay lenses can yield competitive cosmological constraints, emphasizing the importance of accurate prior knowledge of lens populations.

Findings

Approximately 400 time delay lenses can constrain Omega_m and Omega_Lambda with precision comparable to other methods.

Sample sizes of around 100 lenses can measure H_0 with a few percent error.

Inaccurate prior knowledge broadens the constraints, underscoring the need for reliable sample characterization.

Abstract

Upcoming ground and space based observatories such as the DES, the LSST, the JDEM concepts and the SKA, promise to dramatically increase the size of strong gravitational lens samples. A significant fraction of the systems are expected to be time delay lenses. Many of the existing lensing degeneracies become less of an issue with large samples since the distributions of a number of parameters are predictable, and can be incorporated into an analysis, thus helping to lessen the degeneracy. Assuming a mean galaxy density profile that does not evolve with redshift, a Lambda-CDM cosmology, and Gaussian distributions for bulk parameters describing the lens and source populations, we generate synthetic lens catalogues and examine the relationship between constraints on the Omega_m - Omega_Lambda plane and H_0 with increasing lens sample size. We find that, with sample sizes of ~400 time delay lenses, useful constraints can be obtained for Omega_m and Omega_Lambda with approximately similar levels of precision as from the best of other methods. In addition, sample sizes of ~100 time delay systems yield estimates of H_0 with errors of only a couple of percent, exceeding the level of precision from current best estimates such as the HST Key Project. We note that insufficient prior knowledge of the lens samples employed in the analysis, via under or overestimates in the mean values of the sample distributions, results in broadening of constraints. This highlights the need for sound prior knowledge of the sample before useful cosmological constraints can be obtained from large time delay samples (abridged).