Dark matter searches in the direction of dwarf galaxies with H.E.S.S. and characterization of the gamma-ray emission from the Galactic center and Andromeda galaxy with Fermi-LAT

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 γ rays, which 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 in the direction of dwarf galaxies using the γ-ray data of the H.E.S.S. experiment, an array of five Cherenkov telescopes capable of detecting very high energy γ 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 Galactic center and the morphology of M31 galaxy from the high energy γ-ray data collected by the Fermi-LAT space telescope. We present the characterization of the astrophysical components of these sources which represent the background noise for the identification of a potential dark matter signal. (author)