On the Origin of Temperature Substructure within Merging Clusters of Galaxies: Abell 2256

Abstract

Recent ROSAT PSPC and ASCA observations of several rich clusters of galaxies have revealed complex temperature substructure within the X-ray emitting gas. One of the best and most detailed examples is A2256. Briel & Henry (1994) show four distinct temperature components within the central (<12′) of A2256. The purpose of this paper is to suggest a plausible model, within reasonable parameter space, that explains the origin of the hottest (>8 keV) gas near the core of A2256. We find the temperature substructure in A2256 to be consistent with a model in which A2256 is currently in the early stages of a merger. We attempt to quantify this model by comparison with results from our parameter study of merging clusters of galaxies conducted with a numerical Hydro/N-body code. From this, we estimate that A2256 is actually two systems with a 2:1 mass ratio, whose cores are separated by ∼0.5 Mpc with a relative velocity of nearly 3000 km s-1. The proposed merger axis is projected into the plane of the sky by 45°-50° such that the less massive of the two clusters is approaching the observer. Within the frame work of this model, we find the hot gas (> 8 keV) to be the result of shock heating during the merger event. We also use this model to explain the discrepancy between X-ray and galaxy-based mass estimates for A2256.