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

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 that is unrelated to the hot intracluster medium (ICM) 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; at larger radii, they are anisotropic and therefore are unrelated to the hot ICM. 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 hot ICM. The strong EUV excess that exists in the absence of soft X-ray excess poses formidable problems for the nonthermal (inverse Compton) scenario but may readily be explained as being due to emission lines from a shocked underionized gas.