Institute for Advanced Study Informal Astrophysics Seminar

Gravitational lensing by galaxy clusters has become an important tool in studying galaxies from the first billion years of cosmic time; the clusters act as "cosmic telescopes" and make distant galaxies easier to detect. This unique capability has led to numerous cluster lensing surveys, including the Hubble Frontier Fields program. The success of such programs depends crucially on understanding systematic uncertainties in the cluster lens models. Most models are effectively two-dimensional, assuming that all of the lensing mass lies at the redshift of the cluster. I will describe the first full set of three-dimensional lens models for the Frontier Fields, as well as one other massive cluster lens, that account for structure along the line of sight. I will discuss how line-of-sight effects compare with other systematic effects in cluster lens models, and consider lessons for future cluster lensing programs.