Probing general relativity in galactic scales at z ∼ 0.3

General Relativity (GR) has been successfully tested mainly at Solar system scales; however, galaxy-scale tests have become popular in the last few decades. In this work, we investigate the eta PPN parameter, which is commonly defined by the ratio of two scalar potentials that appears in the cosmological linearly perturbed metric. Under the assumption of GR and a vanish anisotropic stress tensor, eta(PPN) = 1. Using ALMA, HST , and VLT/MUSE data, we combine mass measurements, using gravitational lensing and galactic dynamics, for the SDP.81 lens galaxy ( z = 0.299) to constrain eta(PPN). By using a flexible and self-consistent mass profile, our fiducial model takes into account the contribution of the stellar mass and a dark matter halo to reconstruct the lensed galaxy and the spatially resolved stellar kinematics. We infer, after accounting for systematic uncertainties related to the mass model, cosmology, and kinematics, (eta PPN) = 1 . 13( + 0. 03) (-0.03) +/- 0.20 ( sys ), which is in accordance with GR predictions. Better spectroscopy data are needed to push the systematics down and bring the uncertainty to the percentage level since our analysis shows that the main source of the systematics is related to kinematics, which heavily depends on the signal-to-noise ratio of the spectra.

Automated summary

In this work, the eta PPN parameter of the SDP.81 lens galaxy is investigated using mass measurements from gravitational lensing and galactic dynamics. The result shows that eta(PPN) = 1.13(+0.03)(-0.03)+/- 0.20(sys), which is consistent with the predictions of General Relativity. Better spectroscopy data are required to reduce the systematic uncertainties and improve the accuracy.