Galaxy-Scale Strong Lensing Tests of Gravity and Geometric Cosmology: Constraints and Systematic Limitations

TL;DR

This study uses galaxy-scale strong gravitational lensing data to test gravity and measure cosmological parameters, highlighting the potential and current limitations due to systematic uncertainties in galaxy modeling.

Contribution

It combines lensing and stellar velocity data to constrain gravity and cosmology, and assesses the impact of systematic uncertainties on these measurements.

Findings

Constraint on post-Newtonian parameter gamma = 1.01 +/- 0.05

Determination of Omega_Lambda = 0.75 +/- 0.17 assuming flat universe

Systematic uncertainties limit the precision of gravity and cosmology tests

Abstract

Galaxy-scale strong gravitational lenses with measured stellar velocity dispersions allow a test of the weak-field metric on kiloparsec scales and a geometric measurement of the cosmological distance-redshift relation, provided that the mass-dynamical structure of the lensing galaxies can be independently constrained to a sufficient degree. We combine data on 53 galaxy-scale strong lenses from the Sloan Lens ACS Survey with a well-motivated fiducial set of lens-galaxy parameters to find (1) a constraint on the post-Newtonian parameter gamma = 1.01 +/- 0.05 and (2) a determination of Omega_Lambda = 0.75 +/- 0.17 under the assumption of a flat universe. These constraints assume that the underlying observations and priors are free of systematic error. We evaluate the sensitivity of these results to systematic uncertainties in (1) total mass-profile shape, (2) velocity anisotropy, (3) light-profile shape, and (4) stellar velocity dispersion. Based on these sensitivities, we conclude that while such strong-lens samples can in principle provide an important tool for testing general relativity and cosmology, they are unlikely to yield precision measurements of gamma and Omega_Lambda unless the properties of the lensing galaxies are independently constrained with substantially greater accuracy than at present.