Searching for Quadruply Lensed Quasars in Large Imaging Surveys

Abstract

Quadruply lensed quasars, where a lens galaxy produces four images of a background quasar, are powerful tools that can be used to study the expansion of the universe, galaxy evolution, and the nature of dark matter. These are a relatively rare occurrence, with fewer than a hundred quadruply-imaged systems of quasars known today. The next generation of ground and space-based telescopes like the Vera C. Rubin observatory and Euclid space telescope are expected to detect thousands of such strongly lensed quasars, which will allow us to do more precise science with these systems. In the first part of this thesis project, we explored the use of quadruply lensed quasars to identify groups of galaxies at intermediate redshifts. Quadruply lensed quasar images which are highly asymmetric point to the presence of a group/cluster of galaxies in the vicinity of the lens which contributes to the lensing. We studied the occurrence of such systems amongst the known quadruply lensed quasars and whether a group or cluster has been identified. In the second half of the project, we developed a prototype of a program to identify quadruply lensed quasar candidates in data from large surveys. The program utilizes the algorithm Schechter and Wynne (2019) discovered to model quadruply lensed quasars. Initial tests of the program on mock lensed quasars and non-lenses showed promising results. We obtained a true positive detection rate of lensed quasars of over 90% and a false positive rate of ∼ 7%.