L'impact des trous noirs les plus massifs de l’Univers sur le coeur des amas de galaxies

Clusters of galaxies are the biggest gravitationally bound objects in the Universe. They contain hundreds to thousands of galaxies, with the biggest and most massive one, the dominant galaxy, located at the centre of the gravitational potential. At the centre of clusters known as cool core clusters, the dominant galaxy hosts a powerful supermassive black hole that is accreting material and generating relativistic jets. These jets create cavities and tremendous perturbations in the intracluster medium. This is called active galactic nucleus feedback, a mechanism by which the cooling of the intracluster medium is counterbalanced by the active galactic nucleus energetic processes. In some of these clusters, observations show that the cluster also hosts a diffuse radio structure known as a radio mini-halo. Radio mini-halos are radio sources centred on the dominant galaxy and have sizes of ~100-500 kpc. They are found in cool core clusters of galaxies, but their origin remains unknown. Indeed, to produce the radio emission on the scale of radio mini-halos, relativistic particles are needed. However, at such large distances from the cluster centre particles should not be relativistic anymore. Currently, one hypothesis to explain their origin involves the re-acceleration of particles through turbulence in the intracluster medium generated from minor mergers. In this Master's thesis, we aim to better understand the origin of these radio structures and to explore other mechanisms that could explain their origin, including turbulence generated by the active galactic nucleus feedback. We have therefore conducted a survey of all the known radio mini-halos. This survey includes two new radio mini-halos discovered by our collaboration with new radio observations from the Karl G. Jansky Very Large Array, namely the radio mini-halo in the nearby and massive cluster of galaxies PKS 0745-191 (z = 0.1028) and the radio mini-halo in the massive cluster of galaxies MACS J1447.4+0827 (z = 0.3755). We conducted a detailed statistical analysis between the properties of the radio mini-halos and the properties of the clusters. In addition to confirming known correlations, our study also explored the relation between radio mini-halos and active galactic nucleus feedback processes. To enable this, the radio emission from the active galactic nucleus located in the central galaxy was spectrally decomposed into a component that traces ongoing accretion and one that traces past outbursts. We discovered previously unknown correlations between the radio mini-halo power and the power of these two components of the active galactic nucleus. We find that the strongest of the two correlations is the one related to the component that traces past outbursts, which is related to the relativistic jets. Furthermore, a new correlation between the radio mini-halo power and the X-ray cavity power, created by the relativistic jets, was discovered. Overall, our study indicates that radio mini-halos are directly connected to the central active galactic nucleus in clusters of galaxies. Therefore, we hypothesize that this feedback may be one of the dominant mechanisms giving rise to radio mini-halos. This could be accomplished by injecting energy into the intracluster medium, which could re-accelerate an old population of particles with enough initial energy. Therefore, active galactic nuclei feedback in cool core clusters of galaxies may not only play a vital role in offsetting cooling in the intracluster medium, but it may also play a fundamental role in re-energizing the population of non-thermal particles that lead to radio mini-halos.

Keyphrases: Radio mini-halos, Jets, Survey, Radio mini-halos, Clusters of galaxies, Active galactic nuclei feedback, Supermassive black holes, Jets, Cavities, Intracluster medium, Radio astronomy, X-ray astronomy, Targets : PKS 0745-191, MACS J1447.4+0827