2000A&A...364..497L

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 (∼10⁶K) 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 (69-190eV) filter passband. The soft excess radial trend (SERT), shown by a plot against cluster radius r of the percentage EUV emission η 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∼6arcmin, inwards of this radius the EUV is absorbed by cold matter with a line-of-sight column density of ≥2.7x10¹⁹cm^–2. The centre of absorption is offset from that of the emission by ∼1arcmin, 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 ∼5-10 times more massive than the hot.