EUV and X-ray observations of Abell 2199: a three-phase intracluster medium with a massive warm component

Various independent ways of constraining key cosmological parameters yielded a consensus range of values which indicates that at the present epoch the bulk of the universe's baryons is in the form of a warm ($\sim$ 10$^6$ K) gas - a temperature regime which renders them difficult to detect. The discovery of EUV and soft X-ray excess emission from clusters of galaxies was originally interpreted as the first direct evidence for the large scale presence of such a warm component. We present results from an EUVE Deep Survey (DS) observation of the rich cluster Abell 2199 in the Lex/B (69 - 190 eV) filter passband. The soft excess radial trend (SERT), shown by a plot against cluster radius $r$ of the percentage EUV emission $\eta$ observed above the level expected from the hot intracluster medium (ICM), behaves as a simple function of $r$ which decreases monotonically towards $r = 0$; it smoothly turns negative at $r \sim$ 6 arcmin, inwards of this radius the EUV is absorbed by cold matter with a line-of-sight column density of $\geq$ 2.7 $\times$ 10$^{19}$ cm$^{-2}$. The centre of absorption is offset from that of the emission by $\sim$ 1 arcmin, and the area involved is much larger than that of the cooling flow. These facts together provide strong evidence for a centrally concentrated but cluster-wide distribution of clumps of cold gas which co-exist with warm gas of similar spatial properties. Further, the simultaneous modeling of EUV and X-ray data requires a warm component even within the region of absorption. The phenomenon demonstrates a three phase ICM, with the warm phase estimated to be $\sim$ 5-10 times more massive than the hot.