Properties of cluster satellites in hydrodynamical simulations

Abstract

We analyse the dynamical and thermal evolution of dark matter and the intracluster medium in hydrodynamical N-body simulations of galaxy clusters. Starting from a sample of 17 high-resolution objects, with virial mass ranging from 3 × 1014 to 1.7 × 1015h−1 M⊙, we follow the build-up of the systems in dark matter and hot gas through the repeated merging of satellites along their merging history trees. We measure the self-bound mass fraction of subhaloes as a function of time after the merging, estimate the satellite mean orbital properties as a function of the mass ratio with the main cluster at merging time, and study the evolution of their internal velocity dispersion, gas temperature and entropy as the substructure is disrupted by various dynamical processes, eventually reaching thermodynamic equilibrium in the gravitational potential of the main cluster. We model some relevant properties of subhalo orbits, as the time of the first pericentric and apocentric passages, and the typical distances and velocities at the corresponding times. This survival study can be used to interpret the dynamics of observed merging clusters; as an example, we apply our results to the system 1E0657-56. We show that, in the light of our results, the most likely interpretation of the data for this cluster points to the merger of a small group with mass M≈ 1 × 1013h−1 M⊙ with a massive cluster with M≈ 1.3 × 1015h−1 M⊙.