Dark matter constraints of galaxy clusters hosting diffuse radio emissions

Khanye, Nthabiseng F.
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The existence of dark matter (DM) in the universe is extremely important as it explains the rotation of galaxies and hierarchical formation of astrophysical structures. However very little information is known about the formation, nature and interaction properties of DM. Attempts to directly observe DM have not yielded any conclusive results, making it impossible to directly study its physical composition and how it fundamentally interacts with itself and other matter in the universe. This elusive nature of DM has made us turn into indirect detection studies, so that we can be able to constrain some of its physical properties. One of the expected properties of DM particles such as WIMPs (i.e Weakly Interacting Massive Particles) is for them to annihilate inside DM halos found in galaxies and clusters. The annihilating WIMP particles are then expected to result in the production of standard model particles such as electrons and positrons which can lead to the occurrence of observable multi-frequency emissions (such as radio, X-ray etc...) when the produced electrons and positrons interact with magnetic fields and other particles found in galactic and (galaxy) cluster environments. In this thesis we study the multi-frequency implications of DM annihilation in galaxy clusters that host diffuse radio emission by incorporating archival radio observations of said clusters. We focus on two massive and optically rich galaxy clusters, namely Abell 1689 and Abell 520. We assume that the diffuse radio emission found in these clusters is a by-product of the synchrotron radiation produced when electrons resulting from DM annihilation come into contact with cluster magnetic fields. We also present new multifrequency radio analyses of the A1689 galaxy cluster using archival radio observations from six different radio surveys, to study the radio properties of the cluster and its diffuse radio emission
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2022