A Study of the Dynamics and Substructure of a Sample of Nearby Abell Clusters of Galaxies

Recent multiwavelength observations of galaxy clusters suggest that extended radio sources (e.g., Wide-Angle Tailed (WAT) and Narrow-Angle Tailed (NAT) sources) are more likely to be found in clusters with X-ray substructure and in some puzzling cases (i.e., WATs) no cooling flows. These findings prompt us to ask if cluster mergers have any effect on the morphology of extended radio sources and on cluster cooling flows. We used two approaches for answering these questions. First, we performed a multiwavelength study of galaxy clusters (0.06 < z < 0.09) aimed at identifying their dynamical state. Thus, we analyzed the (1) X-ray substructure of ROSAT PSPC observations. (2) 1-D, 2-D, and 3-D substructure of the spatial and kinematical distribution of the cluster galaxies as determined from my own observations at the Bok 2.3m and ARC 3.5m telescopes and from published data. (3) morphology of the radio sources from their VLA radio images. Second, I performed new N-body/Hydrodynamics numerical simulations of the evolution of a cooling flow during galaxy cluster mergers. The main results of my work are: I detected significant X-ray substructure and a very intriguing alignment between a local X-ray surface brightness elongation and the bending directions of the WAT jets in WAT clusters. Moreover, our multiwavelength study of the entire sample finds that the morphology of the WATs and some NATs can only be explained if the radio sources are moving with relative velocities (with respect to the cluster gas) in excess of 1000 km/s. However, I measured very small peculiar velocities for the radio galaxies. Thus, the gas has to have very large bulk flow velocities in order to bend the radio emitting plasma. We propose that a cluster-cluster merger is a suitable mechanism for stirring the gas and creating the observed substructure. My numerical simulations determine that cluster-cluster mergers affect cluster cooling flows. We show that some head-on mergers destroy cooling flows while other leave them intact. The destruction of the cooling flow depends on the nature of the merger (e.g., mass ratio and gas content) and on the nature of the cooling flow (i.e., mass accretion rate).