Two‐Temperature Intracluster Medium in Merging Clusters of Galaxies

We investigate the evolution of intracluster medium during a cluster merger,explicitly considering the relaxation process between the ions and electrons byN-body and hydrodynamical simulations. When two subclusters collide each other,a bow shock is formed between the centers of two substructures and propagate inboth directions along the collision axis. The shock primarily heats the ionsbecause the kinetic energy of an ion entering the shock is larger than that ofan electron by the ratio of masses. In the post-shock region the energy istransported from the ions to electrons via Coulomb coupling. However, since theenergy exchange timescale depends both on the gas density and temperature,distribution of electron temperature becomes more complex than that of theplasma mean temperature, especially in the expanding phase. After the collisionof two subclusters, gas outflow occurs not only along the collision axis butalso in its perpendicular direction. The gas which is originally located in thecentral part of the subclusters moves both in the parallel and perpendiculardirections. Since the equilibrium timescale of the gas along these directionsis relatively short, temperature difference between ions and electrons islarger in the directions tilted by the angles of $\pm 45^\circ$ with respect tothe collision axis. The electron temperature could be significantly lower thatthe plasma mean temperature by $\sim 50 %$ at most. The significance of ourresults in the interpretation of X-ray observations is briefly discussed.Comment: 20 pages, 11 figures, Accepted for publication in Ap