On the extreme-ultraviolet emission from galaxy clusters

An extremely soft X-ray excess throughout galaxy clusters has been claimed as a new feature of these systems, with important physical implications. We have reexamined this feature in the five clusters for which it has been discussed, using the most recent X-ray absorption cross sections, X-ray data processing techniques, and a consistent set of H I data. For the Virgo cluster, we find that the spectrum can be fitted with a single-temperature thermal plasma and an X-ray absorption column that is not significantly different than the Galactic H I column. The results for Abell 1367, Abell 1656 (Coma), Abell 1795, and Abell 2199 are similar in that the difference between the X-ray absorption column and the Galactic H I 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 H I column more than 3 sigma above the X-ray absorption column (Coma, with one location with a 3.6 sigma difference). We conclude that there is no strong evidence for the extremely soft X-ray excess in galaxy clusters.