Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-01-08
Astronomy and Astrophysics
Astrophysics
To be presented at the Atlanta AAS meeting
Scientific paper
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 $\sim$ 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), reveals that $\eta$ is 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 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 $\sim$ 5-10 times more massive than the hot.
Bonamente Massimiliano
Lieu Richard
Mittaz Jonathan P. D.
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