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Astron. Astrophys. 364, 497-500 (2000)

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

R. Lieu 1, M. Bonamente 2 and J.P.D. Mittaz 3

1 University of Alabama, Department of Physics, Huntsville, AL 35899, USA
2 Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95125 Catania, Italy
3 UCL, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK

Received 31 August 2000 / Accepted 6 September 2000


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 ([FORMULA] 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 [FORMULA] observed above the level expected from the hot intracluster medium (ICM), behaves as a simple function of r which decreases monotonically towards [FORMULA]; it smoothly turns negative at [FORMULA] 6 arcmin, inwards of this radius the EUV is absorbed by cold matter with a line-of-sight column density of [FORMULA] 2.7 [FORMULA] 1019 cm-2. The centre of absorption is offset from that of the emission by [FORMULA] 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 [FORMULA] 5-10 times more massive than the hot.

Key words: galaxies: intergalactic medium – galaxies: cooling flows

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001