Studying the most energetic events since the big bang: mergers in clusters of galaxies

Abstract

Galaxy clusters are the largest gravitationally bound objects in the Universe, which are formed via cluster mergers. Major mergers are the most energetic events since Big Bang, releasing as much as 1064 ergs of energy and heating up the intracluster medium (ICM) up to 107−8 K. These merging events create shock and cluster-wise turbulences, which stir the whole intra-cluster medium (ICM). Any such activities can be imprinted in the X-ray emission and can be seen by creating X-ray density, surface brightness, temperature, pressure, and entropy maps. Disturbed morphology in any of the above maps is direct evidence of cluster merger. Previous studies show that radio relics and radio halos are associated with the merging, unrelaxed clusters, whereas radio mini-halos are associated with the relaxed cool core clusters. In order to have a better understanding of the source of diffuse radio emissions in clusters, information from both the X-ray and radio data should be studied. Results from radio (GMRT and VLA) and X-ray (Chandra) investigations of three galaxy clusters are presented in this thesis (AS1063, A1914, and A85). We use three alternative methods to create high-resolution X-ray thermodynamic maps for all three clusters (i.e., the adaptive circular binning (ACB), the Weighted Voronoi Tessellation (WVT), and Contour binning (Contbin)) using Chandra X-ray archival observations. We document a significant “surface brightness excess” in AS1063 that extends along the northeast and southwest axes and may be a component of a cosmic web filament. This also denotes the cluster’s continuing merging processes, which partially disrupt the cool core and create a cluster with a disturbed and non-cool core. We also determined the cluster’s 1.2 Mpc large-scale radio halo’s overall flux. We assumed that AS1063 would experience cluster-wide turbulence as a result of the continuing merger processes, which would aid in the relativistic electrons’ re-acceleration and produce the large-scale radio halo.