Taia Kronborg

Title: Gravitational lensing of SNLS Supernovae

A thesis submitted for the degree of Doctor of Philosophy on September 3, 2009.

Dark Cosmology Centre Niels Bohr Institute
The Graduate School
of Science
Faculty of Science
University of Copenhagen
Denmark

Supervisor:
Kristian Pedersen

Abstract

Gravitational lensing of SNLS Supernovae

Type Ia supernovae have become an essential tool of modern observational cosmology. By studying the distance-redshift relation of a large number of supernovae, the nature of dark energy can be unveiled. Distances to Type Ia SNe are however affected by gravitational lensing which can induce systematic effects in the measurement of cosmology.

The majority of the supernovae is slightly demagnified where as a small fraction is significantly magnified due to the mass distribution along the line of sight. This causes naturally an additional dispersion in the observed magnitudes. There are two different ways to estimate the magnification of a supernova.A first method consists in comparing the supernova luminosity, which is measured to about 15% precision, to the mean SN luminosity at the same redshift. Another estimate can be obtained from predicting the magnification induced by the foreground matter density modeled from the measurements of the luminosity of the galaxies with an initial prior on the mass-luminosity relation of the galaxies. A correlation between these 2 estimates will make it possible to tune the initially used mass-luminosity relation resulting in an independent measurement of the dark matter clustering based on the luminosity of SNe Ia. vidently, this measurement depends crucially on the detection of this correlation also referred to as the lensing signal. This thesis is dedicated to the measurement of the lensing signal in the SNLS 3-year sample.