Properties of Galaxy Dark Matter Halos using galaxy-galaxy weak lensing in the CFHTLS-Deep

Abstract

<p>Gravitational lensing can be used as a direct probe of the distribution of dark matter around galaxies , groups, and clusters, making it a powerful tool in astrophysics. In this thesis, we introduce the basics of gravitational lensing and weak gravitational lensing. Using weak lensing to study the ensemble-averaged properties of a population of objects, we present a study of galaxy-galaxy lensing of galaxy-sized dark matter halos using data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep.</p> <p>We calculated the average velocity dispersion for an L_* galaxy at a redshift of 0.54 to be 113 ± 9 kms^-1, with a mass of 1.7 ± 0.3 x 10¹² h^{- 1}M_⊙. We present the first conclusive evidence for non-spherical galaxy dark matter halos. Our results favour a dark matter halo with an ellipt icity of 0.70 ± 0.18 at > 5σ when averaged over all galaxies. If the sample of foreground lens galaxies is selected by colour , we detect non-spherical halos for all 4 samples except a green subsample. We also consider samples of galaxies divided by colour , redshift and luminosity. Our luminosity samples allowed us to calculate a B-band Tully-Fisher relation which is consistent with theoretical predictions.<br />From our data, we do not detect any evolut ion in galaxy dark matter halos from a redshift of 0. 78 to 0.39, corresponding to no evolut ion from when the Universe was 6.6 Gyr to 9.1 Gyr old in a ACDM cosmology.</p>