Purva Diwanji

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Physics and Astronomy

Committee Chair

Stephen A. Walker

Committee Member

Ming Sun

Committee Member

Max Bonamente

Committee Member

Richard Lieu

Research Advisor

Stephen A. Walker


Galaxies--Clusters, Galaxy mergers, X-ray astronomy


Galaxy clusters, found at the nodes of the large-scale structures in the universe, are the most massive gravitationally bound and virialized structures in the Universe. They are formed via accretion, gravitational infall, and hierarchical mergers of smaller sub-clusters and galaxy groups. Mergers of galaxy clusters are the most energetic events in the Universe after the Big Bang, wherein the sub-clusters collide at velocities of ~1000km/s, releasing energy of the order of 10^(64) ergs. During such a merger, the galaxies and dark matter of both clusters interact only gravitationally and move unhindered through the region of the collision. This dissertation presents findings from the new deep Chandra observations (256 ks) of the merging galaxy cluster SPT-CLJ 2031-4037. Our observations reveal intricate structures seen in a major merger akin to the Bullet Cluster. The X-ray data confirm the existence of two shock fronts, one to the northwest and one to the southeast, by directly measuring the temperature jump of gas across the surface brightness edges. The stronger shock front in the northwest has a density jump of 3.11 +/- 0.32 across the sharp surface brightness edge and a Mach number M = 3.23^(+0.89)_(-0.56), which makes this cluster one of the rare merging systems with a Mach number M>2. The northwestern shock is used to compare two models for shock heating - the instant heating model and the Coulomb collisional heating model, and it is determined that the temperatures across the shock front agree with the Coulomb collisional model of heating. For the shock front in the southeastern region, there is a density jump of 1.53 +/- 0.14 and a Mach number M = 1.36 ^(+0.09)_(-0.08). In addition, I will also present new results of cold fronts in the nearby Perseus Cluster, which are also produced by galaxy cluster merging activity, and provide insights into its merger history.



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