ABSTRACT

We describe a program of N-body simulations of clusters of galaxies. Results concerning merging histories and the kinematic properties of multiple nuclei are presented.

THE MODELS

We have completed nine N-body evolutions of models containing 50 galaxies using a total of N = 4 × 104 particles. The models are fully self-consistent in that each galaxy is represented as an extended structure containing many particles and the total gravitational potential arises from the particles alone. The evolutions are carried out with a direct N-body code based on the Barnes and Hut (1986) TREE algorithm for computing the gravitational potential; it is the code developed by Lars Hernquist (1987, 1990) with some modifications (Bode, Cohn, and Lugger 1993).

For all the models, 10% of the particles are ‘luminous’ and the rest represent ‘dark’ matter; the former are given a smaller softening length than the latter. The dark matter is apportioned between galaxy halos and a smoothly distributed cluster background. The percentage of mass initially in this intra-cluster background, β, is varied from 50% to 90%.

The initial mass distribution of the galaxies follows a Schechter function. For β = 50%, the smallest galaxy contains 125 particles and the largest 3500 particles. Galaxies are given a core-halo structure by identifying the most bound particles in each galaxy as luminous. Since the total amount of mass in the cluster is the same for all models, increasing β has the effect of removing mass from the galaxy halos and distributing it through the cluster.