paper

Subcluster Merger and Galaxy Infall in A2151

arXiv:astro-ph/9412004 · doi:10.1086/117330

Abstract

We have obtained a 12.5 ksec image of the Hercules Cluster, A2151, with the {\it ROSAT} PSPC. Comparison of the optical and X-ray data suggest the presence of at least three distinct subclusters in A2151. The brightest X-ray emission coincides with the highest-density peak in the galaxy distribution, and is bimodal. The northern subclump, distinct in position and velocity, has {\it no} detectable X-ray gas. The eastern subclump, apparent in the optical contour map, is indistinguishable from the main clump in velocity space but is clearly visible in the X-ray image. X-ray spectra derived from the central peak of emission yield a best-fit temperature of 1.6 keV. The emission coincident with the eastern clump of galaxies is cooler, 0.8 keV, and is outside the 90\% confidence intervals of the central peak temperature. We suggest that the eastern and central subclusters have recently undergone a merger event. The lack of X-ray emission to the north suggests that those galaxies do not form a physically-distinct structure (i.e. they are not located within a distinct gravitational potential), but rather that they are falling into the cluster core along the filament defined by the Hercules Supercluster.

To appear in the March 1995 issue of AJ, LaTeX, PostScript text and figures available by anonymous ftp from kula.phsx.ukans.edu

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