Oral Presentation

Environments of Time-Delay Gravitational Lenses

Kenneth Wong (ASIAA) et al.

Strongly-lensed quasars represent a unique probe of cosmological parameters, independent of and complementary to constraints from supernovae, CMB observations, and BAOs. With a precise measurement of the time delay between the multiple quasar images and an accurate mass model for the lens galaxy, the Hubble constant can be recovered. However, mass along the line of sight to the lens can lead to a bias in the recovered parameters. Various methods can be used to correct for this bias, such as using relative number counts calibrated to cosmological simulations, or assigning masses to individual halos in the field. The latter method requires substantial observational and computational resources to account for perturbers at different redshifts. I present a new method for efficiently characterizing these effects, which accounts for the most significant perturbers explicitly while treating the majority of the perturbers with an approximation that greatly reduces the necessary computations. Using spectroscopic and photometric data along the line of sight to known lenses, we construct realistic lens environment to show that we can accurately recover the Hubble constant with minimal bias using this methodology.