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Galaxy mass profiles from strong gravitational lensing

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Title: Galaxy mass profiles from strong gravitational lensing
Authors: O'Riordan, Conor
Item Type: Thesis or dissertation
Abstract: In this thesis we develop a theory for constraining power-law mass profiles with strong lensing observations. We account for both positional and flux information and show that strong lensing can provide precise constraints on the mass profiles of galaxies, and, that these constraints apply over more than just the radial range of the images. Beginning with the circular power-law model, we find an analytic expression which relates the image position ratio and the flux ratio to the slope. We then derive an expression for the uncertainty on the slope. This result is verified by finding the slope uncertainty in a series of mock observations where a circular lens is fit with a power-law ellipsoid. We then extend this analysis to elliptical systems. Here we show that for any two-image system the slope uncertainty is determined by the expression for the circular case. The constraint therefore also relies on a combination of positional and flux information. In the four-image systems we identify two separate cases. First, when the source is aligned with the axis we again find an analytic expression for the slope uncertainty. Second, in the general four-image systems we show that the slope is strongly constrained by the positional information alone. Finally we formulate a truncated power-law model which we use with mock observations to show that the slope interior to the lensed images is constrained, contrary to the standard view expressed in the literature. The truncated power-law results are then used to formulate a broken power-law, a more flexible lens model with an inner and outer slope, continuous across a break radius. Fitting to mock observations with the broken power-law shows that the inner and outer slopes are well constrained. This shows for the first time that lensing observations alone can constrain power-law mass profiles of lens galaxies in significant detail.
Content Version: Open Access
Issue Date: Aug-2020
Date Awarded: Feb-2021
URI: http://hdl.handle.net/10044/1/88167
DOI: https://doi.org/10.25560/88167
Copyright Statement: Creative Commons Attribution NonCommercial Licence
Supervisor: Warren, Stephen
Sponsor/Funder: Science and Technology Facilities Council (Great Britain)
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses

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