Date of Award
Doctor of Philosophy (PhD)
Astronomy., Cosmology., Galaxies., Chandra x-ray observatory (U.S.)
Shocks are the most important sources of heating in galaxy clusters. Despite their rarity, they have been studied extensively on individual scales. However, a systematic sample study is necessary to recognize any general pattern in merger shocks. With this goal, we constructed a Sample of Chandra ClustErs with Robust Shocks (SoCCERS) to study shock properties, the related merger phenomena, and particle acceleration. The sample includes 16 galaxy clusters where shocks are robustly detected with the Chandra X-ray data, from the surface brightness jumps and the changes on thermodynamic properties. The sample can be further divided into two categories: with or without diffuse radio emission (DRE). We begin by studying merger shocks in 3C89 and Abell 665. 3C89 is a unique bow shock system associated with a wide angle tail (WAT) radio galaxy and has several intriguing substructures. The bow shock in this system is consistent with the Mach number M ~1.6. Abell 665 hosts a bright radio halo. Our study found a very strong merger shock with the Mach number M ~3 in Abell 665 which is weakly correlated with the radio relic. This newly discovered strong shock provides a great opportunity to study the re-acceleration model with the X-ray and radio data combined. We compared several shock parameters from SoCCERS clusters such as i) shock strength vs. system temperature vs. offset from the cluster centroid, ii) cold front vs. shock shape. We found that the clusters with DRE tend to have higher system temperatures than clusters without DRE. Also, from all known shock front/cold front pairs, it appears that the physical scale of the shock front is correlated with the respective cold front. A comparison between the shock standoff distance and the Mach number suggests that cores are continuously shrinking in size by ram pressure stripping. Finally, we analyzed cool core strength and concluded that it correlates with the projected X-ray - BCG offset (a disturbance indicator).
Dasadia, Sarthak, "Shocking features in merging galaxy clusters" (2017). Dissertations. 141.