Chloé Féron

Title: Testing the Lambda-Cold Dark Matter model at galactic scales

A thesis submitted for the degree of Doctor of Philosophy (PhD) on October 8, 2008.

Dark Cosmology Centre, Niels Bohr Institute
Faculty of Science, University of Copenhagen

Supervisor:
Jens Hjorth

Co-supervisor:
Steen H. Hansen

Abstract

Testing the Lambda-Cold Dark Matter model at galactic scales

The A-Cold Dark Matter model has gained the place of cosmological paradigm, yet its success at explaining the large-scale universe is not reproduced at galactic scales. This thesis focus on aspects of testing the cosmological paradigm at galactic scales, by gaining insights both theoretically and observationally into the dark and baryonic matter distributions of galaxies.

Nonextensive statistical mechanics, a generalization of classical statistical mechanics designed to describe long-range interaction systems, has been proposed recently to predict the structure of dark matter halos, using stellar polytropes. A careful comparison of structural radial profiles of stellar polytropes with those of simulated dark matter halos is presented in this thesis. It establishes that nonextensive statistical mechanics is unable to predict the structure of dark matter halos.

Gravitational lensing provides a promising way of constraining the mass distribution of disk galaxies and measure their mass-to-light ratio. Unfortunately, only seven disk-galaxy lenses are known to date. Here is presented the first automated spectroscopic search for disk-galaxy lenses, using the Sloan Digital Sky Survey database.

Eight disk-galaxy lens candidates are studied, using imaging and long-slit spectroscopy observations. Two new gravitational lenses are presented, which are probable disk and S0 galaxies, as well as four very interesting disk-galaxy lens candidates, and two probable lenses where the lens galaxy is either an S0 or elliptical galaxy. Higher resolution observations are needed to further study these systems.

These results open promising perspectives for enlarging the sample of known disk-galaxy lenses, and gaining further understanding of the baryonic and dark matter distributions in disk galaxies.