Celine Armand – Phd’s defense – nov. 18, 2020

Cosmological and astrophysical observations suggest that 85% of the total matter of the Universe is of unknown form, the so-called dark matter. The nature of dark matter still remains a mystery to this day and its discovery represents one of the biggest challenges of modern fundamental physics. The work presented in this thesis is performed within the indirect detection framework where dark matter particles would produce some signal by self-annihilating and creating observable particles including gamma rays, which, in turn, may be detected by ground- and space-based telescopes. Several kinds of promising targets for dark matter searches are available such as the Milky Way Galaxy, dwarf galaxies, and the neighboring Andromeda galaxy (M31) which are expected to have a high dark matter content. The first part of our work is dedicated to the search for dark matter towards dwarf galaxies using the gamma ray data of the H.E.S.S. experiment, an array of five Cherenkov telescopes capable of detecting very high energy gamma rays. We present the constraints obtained on dark matter studying three different kinds of dwarf galaxies from the theoretical to the observational and experimental aspects. The second part of our work consists in studying the morphology of M31 galaxy from the high energy gamma ray data collected by the Fermi-LAT space telescope. We present the characterization of the astrophysical components of this source which represent the background noise for the identification of a potential dark matter signal.