2000/01/08 by Richard Lieu, Lieu, Richard, Massimiliano Bonamente +3
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0001127
To be presented at the Atlanta AAS meeting
arxiv created 2000/01/08 · arxiv updated 2009/12/01
Various independent ways of constraining the Hubble constant and the baryonic content of the universe finally converged at 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 ∼ 106 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 η observed above the level expected from the hot intracluster medium (ICM), reveals that η is a simple function of r which decreases monotonically towards r = 0; it smoothly turns negative at r ∼ 6 arcmin, inwards of this radius the EUV is absorbed by cold matter with a line-of-sight column density of ≥ 2.7 × 1019 cm-2. The area of absorption 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.