Exploring the Dark and Dusty Universe with Gravitational Lensing
Abstract
In this thesis, gravitational lensing is used as a tool to study the dusty and dark distant universe. The first part of the thesis presents the first systematic study of dust extinction in lensing galaxies using gravitationally lensed background quasars. It is shown the these galaxies vary greatly both in the amount and type of dust and can vary significantly from the dust seen in the Milky Way. This is a significant result since, due to lack of knowledge on extragalactic dust, Milky Way type of extinction is frequently assumed when calibrating high precision cosmological data (e.g. supernova Ia dark energy surveys).
Studying the dust extinction in the very large lensing data sets which will arise serendipitously in future planned space based missions (such as the SNAP dark energy survey), it will be possible to constrain the evolution of dust with redshift and morphology, providing these surveys with an independent estimate of one of their major sources of systematic error. The second topic of this thesis is dark matter in galaxies and clusters. It starts with a theoretical study of the strong lensing properties of the Sérsic profile and compares it to those of the NFW profile. The NFW profile is the standard description of dark matter, but recently it has been suggested that the Sérsic profile, more commonly used to describe baryonic matter in galaxies, may be a more accurate description. The results show that it is often possible to find an NFW profile which accurately reproduces the strong lensing signal of a Sérsic profile. However, in other cases, the difference between these profiles could contribute to explaining the discrepancy in the mass and concentration estimates from strong lensing on the one hand, and from weak lensing and X-ray measurements on the other. Next, a mass reconstruction of the galaxy cluster Abell 2218 is deduced using strong lensing constraints. The mass distribution is found to be bimodal in agreement with previous models of Abell 2218. However, the second large scale dark matter clump is found to be larger and with a flatter core than previous models have found. This flatness is further supported by "blind tests" which do not place galaxy sized components near its centre. An analysis of the cluster galaxies in velocity space finds evidence for two substructures corresponding to the two large scale dark matter halos. The X-ray data and the distribution in velocity space are found to support the interpretation that the bimodal mass distribution arises from a cluster merger. It is also shown that strong lensing constraints can reliably detect substructure,dark or luminous, if the substructure is massive or locally perturbs a system. Finally, the thesis closes with a short discussion on two smaller projects related to lens modelling. The first is the concentration of the mass distribution in the galaxy cluster Abell 1689, which is found to be marginally higher than values expected from numerical simulations. The second is the possible lensing of the gamma ray burst GRB 050509B. This gamma ray burst is associated both with an elliptical galaxy and with a galaxy cluster, which could be foreground objects lensing the burst. It is shown, assuming that the gamma ray burst is a backgrounds ource, that it is most likely only weakly affected by lensing.- Publication:
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Ph.D. Thesis
- Pub Date:
- December 2007
- Bibcode:
- 2007PhDT........73E