Abstract:
X-ray emission from clusters of galaxies is due to thermal Bremsstrahlung from a hot thin gas in the intergalactic medium. The gas is generally considered to be smoothly distributed with a size of approximately 3 Mpc. X-ray imaging with the Einstein Observatory has shown that the surface brightness departs from a symmetrical distribution or has multiple peaks (sub-structure) in nearly 30% of the clusters. Recent ROSAT observations show (1) the relaxed clusters like Coma and Abell 2256 have significant sub-clustering due to on-going mergers, (2) the existence of filamentary X-ray structure in the central regions of the cooling flow clusters, and (3) the dominance of dark matter and the lowest metal abundance in the gas in a small group of galaxies, NGC 2300. These results from ROSAT are reviewed here
