Probing the nature of dark matter with the power spectrum of small-scale mass structure in massive elliptical lens galaxies

Whereas the predictions from the phenomenological dark-matter models are practically indistinguishable with respect to the expected number of individual massive sub-galactic structures, the critical difference lies in the abundance and the population characteristics of substructures with lower masses. The phenomenon of the galaxy-galaxy strong gravitational lensing provides a unique opportunity to search for such low-mass substructures inside galaxies that happen to act as gravitational lenses on more distant galaxies, serendipitously located along the same line of sight. In this thesis, we present a novel statistical approach to investigate the collective perturbative effect of these low-mass sub-galactic structures on the lensed images of the background galaxies, such as Einstein rings or gravitational arcs. Our approach is based on Hubble Space Telescope (HST) observations of galaxy-galaxy strong gravitational lens systems, the subsequent computational modelling of the observed gravitational-lensing effect and, finally, the Fourier analysis of the anomalies revealed in the lensed images