Speaker
Description
General Relativity (GR) has been extensively tested at Solar System scales; in recent decades, galaxy-scale tests have become popular. In particular, recent works have focused on the so-called gravitational slip parameter $\eta_\text{PPN}$, which quantifies the spatial curvature generated per unit mass. Under GR, and assuming a vanishing anisotropic stress tensor, $\eta_\text{PPN} = 1$. In this work, we use data from ALMA, HST, and VLT/MUSE to constrain the gravitational slip for the elliptical lens galaxy SDP.81 ($z_l = 0.299$) by combining mass measurements from gravitational lensing and stellar dynamics. We adopt a self-consistent mass model that 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. For our fiducial model, we find $\eta_\text{PPN} = 1.13_{-0.03}^{+0.03} \pm 0.20^\text{sys}$, where the second term accounts for uncertainties from the mass model, cosmology, and kinematics. This result is consistent with GR predictions; however, we identify stellar kinematics as the dominant source of systematics. Improved spectroscopic data will be essential to reduce these uncertainties to the percentage level and improve probes on the slip parameter at high-redshift galaxies.
