Orateur
Description
Time-delay cosmography with strongly lensed quasars provides a direct, one-step measurement of the Hubble constant in the local Universe, independent of the cosmic distance ladder and early-Universe probes. By measuring the time delays between multiple images of a variable background quasar, and modeling the gravitational potential of the deflector galaxy, one can infer absolute distances that scale inversely with the Hubble constant. This technique therefore offers a powerful and complementary approach to addressing the current tension in measurements of H0.
In this talk, I will present updated cosmological constraints from strongly lensed quasars based on a new analysis by the TDCOSMO collaboration. We combine high-resolution imaging from the James Webb Space Telescope (JWST), spatially resolved stellar kinematics of the lens, and improved treatments of line-of-sight effects to refine our models of the deflector galaxies. In particular, we implement a framework that fully accounts for the mass-sheet degeneracy in the lens mass density profile. This degeneracy is constrained using new stellar velocity dispersion measurements from JWST resolved spectroscopy. These advances significantly reduce key systematic uncertainties and strengthen the robustness of time-delay cosmography as a precision probe of late-time cosmology. This talk will be given on behalf of the TDCOSMO collaboration.