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Session 21 - Galaxies and Clusters of Galaxies.
Oral session, Monday, June 10
Hybrid N-body/hydrodynamical simulations of head-on collisions between clusters of galaxies (eg. Evrard 1990, Roettiger et al. 1993, Pearce et al. 1994) have demonstrated that the effects of such a collision can be observable for several Gyr after the event. These effects include shock heating of the intracluster gas, distortion of X-ray isophotes along the collision axis, and destruction of hydrostatic equilibrium (as shown by the displacement of the gas centroid from that of the galaxy distribution). In the presence of other nearby clusters, however, it is reasonable to expect that collisions with non-negligible impact parameters could take place. As the clusters in such off-center collisions would develop significant large-scale angular momentum, it is interesting to determine how this angular momentum affects the general progress of the collision and how it is distributed with scale in the final merger remnant. We report on simulations of off-axis collisions made using several different impact parameters, impact velocities, and relative cluster masses. We use a hybrid N-body/hydro code based on the piecewise-parabolic method (PPM) and a particle-mesh method (PM). Using a multigrid-based Poisson solver we are able to handle the isolated boundary conditions required for these calculations. Preliminary results for the gas-only problem suggest that the primary shock wave resulting from the collision dissipates most of the clusters' angular momentum in this case.
Program listing for Monday