Hydrodynamic Simulations of a Moving Substructure in a Cluster of Galaxies: Cold Fronts and Turbulence Generation

We perform three dimensional hydrodynamical simulations of a movingsubstructure in a cluster of galaxies. We investigate dynamical evolution ofthe intracluster medium (ICM) in and around the substructure moving radially inthe larger cluster's gravitational potential, and its observationalconsequences. After the substructure passes the larger cluster's center, a bowshock and clear contact discontinuity form in front of it. The contactdiscontinuity looks like a sharp cold front in the X-ray image synthesized fromthe simulation results. This agrees with a structure found in 1E 0657-56. Theflow structure remains laminar before the first turnaround because theram-pressure stripping is dominant over the development of Kelvin-Helmholtzinstabilities on the boundary between the substructure and the ambient ICM. When a subcluster oscillates radially around the larger cluster's center,both Kelvin-Helmholtz and Rayleigh-Taylor instabilities develop well and theflow structure becomes highly turbulent. Around the turnaround, thesubcluster's cold gas is pushed out of its potential well. Therefore, the cold gas component appears to be in front of the subcluster. Arelatively blunt cold front appears in the simulated X-ray image because the contact discontinuity is perturbed by Rayleigh-Taylorinstabilities. This can explain the ICM structure found in A168.Comment: 17 pages, 6 figures, accepted for publication in Ap