Probing small-scale structure in galaxies with strong gravitational lensing

Abstract

OF THE DISSERTATION Probing Small-Scale Structure in Galaxies with Strong Gravitational Lensing by ARTHUR BENJAMIN CONGDON Dissertation Director: Charles R. Keeton We use gravitational lensing to study the small-scale distribution of matter in galaxies. First, we examine galaxies and their dark matter halos. Roughly half of all observed four-image quasar lenses have image flux ratios that differ from the values predicted by simple lens potentials. We show that smooth departures from elliptical symmetry fail to explain anomalous radio fluxes, strengthening the case for dark matter substructure. Our results have important implications for the “missing satellites” problem. We then consider how time delays between lensed images can be used to identify lens galaxies containing small-scale structure. We derive an analytic relation for the time delay between the close pair of images in a “fold” lens, and perform Monte Carlo simulations to investigate the utility of time delays for probing small-scale structure in realistic lens populations. We compare our numerical predictions with systems that have measured time delays and discover two anomalous lenses. Next, we consider microlensing, where stars in the lens galaxy perturb image magnifications. This is relevant at optical wavelengths, where the size of the lensed source is comparable to the Einstein radius of a typical star. Our simulations of negative-parity images show that raising the fraction of dark matter relative to stars increases image flux variability for small sources, and decreases it for large sources. This suggests that quasar accretion disks and