N-body Simulations of Galaxy Cluster Evolution Using Tree-Codes
Session 41 -- Computational Astrophysics II
Display presentation, Wednesday, 1, 1994, 9:20-6:30

## [41.09] N-body Simulations of Galaxy Cluster Evolution Using Tree-Codes

Paul W. Bode, Robert C. Berrington, Haldan N. Cohn, Phyllis M. Lugger (Indiana University)

We present the results of dissipationless $N$-body simulations of clusters containing 100 galaxies; a total of $N=10^5$ particles is used, and each galaxy is an extended structure containing between 125 and 3000 particles. The evolutions are carried out using both a modified version of Hernquist's (1990, J.\ Comp.\ Phys. {\bf 87}, 137) tree-code run on high-end workstations, and the parallel hashed oct-tree code developed by Salmon and Warren (1993, {\it Supercomputing '93}, 12; 1994, J.\ Comp.\ Phys. , in press) run on up to 64 nodes of the Indiana University Intel Paragon. The former code employs spline-kernel softening and we use separate softening lengths for the luminous and dark particles in the galaxy models; the latter code uses Plummer softening with a single softening length. A comparison of these two approaches is presented.

The goal of this work is to investigate the dependence of galaxy interaction rates on cluster velocity dispersion, richness, and dark matter distribution. The scaling with cluster richness is determined by comparison with our extensive set of simulations of 50-galaxy clusters (Bode, Berrington, Cohn, \& Lugger, 1994, Ap.\ J. , in press). We are particularly interested in investigating the formation of a central dominant galaxy by mergers and the development of a density cusp in the distribution of other galaxies about such a dominant galaxy. Since rich clusters are likely to have developed by the merger of smaller groups, we have undertaken a \mbox{series} of simulations of cluster collisions. Results from a head-on, parabolic collision between two 50-galaxy clusters are presented. The effect of such group mergers on the evolution of cluster cores is discussed.

A video visualization of the evolution of several models will be displayed. These animations were created using the AVS software package.