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P. M. Ricker (University of Chicago), C. L. Sarazin (University of Virginia)
As many as half of all nearby (z<0.1) clusters of galaxies show evidence of recent or ongoing merger activity. Some, including Abell 754 and Abell 3395, are thought to be undergoing off-center mergers. Distinguishing such systems from head-on mergers is important because the frequency of offset collisions depends upon the geometry of cluster assembly, which in turn is closely related to the geometry of large-scale structure (e.g., filamentary or sheetlike). It is also important because the presence of even a small amount of angular momentum in a merger increases the equilibration time over the head-on case and may produce small-scale turbulent motions which contribute to nonthermal support of the merger remnant's core. Identifying a merger as off-center thus gives extra insight into the dynamical history and present structure of a cluster. We present new simulations of offset cluster mergers incorporating both gas and dark matter, discussing the dynamical evolution of these systems and observational means for distinguishing them from head-on collisions.
This research has been supported by NASA under NAG 5-3057 and by the ASCI Flash Center at the University of Chicago under DOE contract B341495.
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