Extreme-Ultraviolet Images of the Clusters of Galaxies A2199 and A1795: Clear Evidence for a Separate and Luminous Emission Component

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Abstract
Since all of the five clusters of galaxies observed by the Extreme Ultraviolet Explorer deep survey telescope are found to possess a diffuse EUV emitting component which is unrelated to the virial gas at X-ray temperatures, the question concerning the nature of this new component has been a subject of controversy. Here we present results of an EUV and soft X-ray spatial analysis of the rich clusters Abell 2199 and 1795. The EUV emission does not resemble the X-ray morphology of clusters: at the cluster core the EUV contours are organized, but at larger radii they are anisotropic, and therefore need not have originated from a hydrostatically stable medium. The ratio of EUV to soft X-ray intensity rises with respect to cluster radius, to reach values ~10 times higher than that expected from the virial gas. The strong EUV excess which exists in the absence of soft X-ray excess poses formidable problems to the non-thermal (inverse-Compton) scenario, but may readily be explained as due to emission lines present only in the EUV range. In particular, warm gas produced by shock heating could account for such lines without proliferation of bolometric luminosities and mass budgets.Comment: 13 pages, 7 figures (4 in color), minor typos corrected; ApJL accepte