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 similar to 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.