On the Extreme‐Ultraviolet Emission from Galaxy Clusters

An extremely soft X-ray excess throughout galaxy clusters has been claimed asa new feature of these sytems, with important physical implications. We havereexamined this feature in the five clusters for which it has been discussed,using the most recent X-ray absorption cross sections, X-ray data processingtechniques, and a consistent set of HI data. For the Virgocluster, we find thatthe spectrum can be fit with a single-temperature thermal plasma and with anX-ray absorption column that is not significantly different than the GalacticHI column. The result for Abell 1367, Abell 1656 (Coma), Abell 1795, and Abell2199 is similar in that the difference betweenthe X-ray absorption column andthe Galactic HI column is less than 3-sigma for He/H = 0.09, and for He/H =0.10 only one cluster location leads to a Galactic HI column more than 3-sigmaabove the X-ray absorption column (Coma, with one location with a 3.6-sigmadifference). We conclude that there is no strong evidence for the extremelysoft X-ray excess in galaxy clusters.Comment: 10 pages of figures, 1 LaTeX manuscrip