An X-Ray Temperature Map of the Merging Cluster Abell 2255

We present a spatially resolved map of intracluster gas temperatures in the rich cluster Abell 2255, using ROSAT PSPC data. The intracluster gas is strongly nonisothermal and the temperature distribution supports the conclusions of Burns and coworkers that Abell 2255 is currently undergoing a merger. The hottest regions are near the core, northwest of the center. A map of the ratio of softer to harder X-ray photons reveals an anomalously soft region northeast of the center, coincident with a radio ridge discovered by Burns and coworkers in 1995. We suggest that this cooler region is associated with an infalling group of galaxies that is giving rise to the radio ridge. Meanwhile, a much more substantial recent merger between comparably sized subcluster components can account for the more global merger signatures, which include the extensive central radio halo, the large-scale gas temperature variations, the pair of central-dominant ellipticals, elliptical X-ray isophotes offset from these dominant galaxies, and the very high velocity dispersion of galaxies in the cluster.