Mergers and Non-thermal Processes in Clusters of Galaxies

Clusters of galaxies generally form by the gravitational merger of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. The basic properties of cluster mergers and their effects will be discussed. Mergers drive shocks in the intracluster gas, and these shocks heat the intracluster gas, and should also accelerate nonthermal relativistic particles. Mergers also produce distinctive features in the X-ray images of clusters, including “cold fronts” and cool trails. Chandra and XMM/Newton observations of the X-ray signatures of mergers will be discussed. X-ray observations of shocks and cold fronts can be used to determine the geometry and kinematics of the merger. As a result of particle acceleration in shocks and turbulent acceleration following mergers, clusters of galaxies should contain very large populations of relativistic electrons and ions. Observations and models for the radio, extreme ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles accelerated in these shocks will also be described.