The dynamical evolution of galaxy clusters: Observations and simulations

The effect of subclusters on the development of cD galaxies and the cluster environment is investigated through the use of N-body simulations and radial velocity measurements of the galaxy cluster A2256. All new radial velocity measurements were obtained from the WIYN telescope with the Multi-Object Spectrograph known as Hydra. A total of 236 new radial velocities combined with radial velocities obtained from the literature make a total of 319 measured radial velocities for Abell 2256 (A2256). The cluster simulations are fully self-consistent with each galaxy represented by an distribution of particles, and the gravitational potential of the cluster as a whole arises from the distribution particles alone. All simulations are carried out using a parallelized “tree” algorithm.; A detailed search for the presence of substructure in the 277 cluster members with measured radial velocities is presented. I find strong evidence for a merger event between two groups. The presence of the two groups is strongly supported by the X-ray emission from A2256 (Briel et al., 1991), and the radio emission (Röttgering et al., 1994). In addition I present strong evidence for a third group on the outer reaches of the system, that is beginning the merging process. Evidence for the interaction between the third group and the intra-cluster medium of A2256 is strongly supported by radio observations.; The computer simulations consist of five single-cluster models and five cluster-merger models. The single-cluster models contain 50 galaxies which are represented byN = 80,000 particles. The cluster-crash models consist of two 50-galaxy, single-cluster models on a sub-parabolic glancing collision and are represented by N = 160,000 particles. Results show that the production of a central dominant galaxy is the natural product of the cluster simulations and the cluster-merger models. In fact the cluster-merger models are more conducive to producing a more massive central dominant galaxy than the single-cluster models even though the cluster-merger models show a lower rate of galaxy merging than the single-cluster models.