Diffuse Nonthermal Radio Structures in Galaxy Clusters

Abstract

This thesis presents a systematic search and multi-frequency radio analysis of the galaxy cluster Abell 2811, with the primary objective of identifying and characterizing a cluster that could host a radio megahalo—a recently discovered class of extended, ultra-steep spectrum synchrotron sources in galaxy clusters. Employing deep observations with the Murchison Widefield Array (MWA) in the 88-216 MHz range, I investigate the spatial and spectral properties of diffuse radio emission in Abell 2811, combining advanced imaging, compact source subtraction, and spectral mapping techniques. The cluster reveals a remarkable ultra-steep spectrum radio halo, extending over more than 1 Mpc at the lowest frequencies and exhibiting spectral index gradients indicative of advanced synchrotron ageing and turbulent reacceleration processes. Morphological and spectral index maps show broad, low- brightness extensions typical of megahalos, with a central region of ongoing particle acceleration and peripheral zones shaped by radiative losses. The association between radio and X-ray emission supports a scenario where cluster mergers drive turbulence and magnetic field amplification on megaparsec scales. These results strongly position Abell 2811 as a promising candidate for hosting a megahalo structure, contributing key observational evidence to the population of diffuse nonthermal cluster sources. The findings have important implications for our understanding of particle acceleration, magnetic fields, and the prevalence of large-scale nonthermal phenomena in galaxy clusters, motivating further systematic searches with next-generation radio telescopes.