TEST OF PARAMETRIZED POST-NEWTONIAN GRAVITY WITH GALAXY-SCALE STRONG LENSING SYSTEMS

Based on a mass-selected sample of galaxy-scale strong gravitational lenses from the SLACS, BELLS, LSD and SL2S surveys and using a well-motivated fiducial set of lens-galaxy parameters we tested the weak-field metric on kiloparsec scales and found a constraint on the post-Newtonian parameter gamma=0.995(-0.047)(+0.037) under the assumption of a flat Lambda CDM universe with parameters taken from Planck observations. General relativity (GR) predicts exactly gamma=1. Uncertainties concerning the total mass density profile, anisotropy of the velocity dispersion and the shape of the light-profile combine to systematic uncertainties of similar to 25%. By applying a cosmological model independent method to the simulated future LSST data, we found a significant degeneracy between the PPN gamma parameter and spatial curvature of the Universe. Setting a prior on the cosmic curvature parameter -0.007< Omega(k) <0.006, we obtained the following constraint on the PPN parameter: gamma=1.000(-0.0025)(+0.0023). We conclude that strong-lensing systems with measured stellar velocity dispersions may serve as another important probe to investigate validity of the GR, if the mass-dynamical structure of the lensing galaxies is accurately constrained in the future lens surveys.