Diffuse EUV Emission from Clusters of Galaxies

Abstract

Diffuse EUV emission has been detected in five clusters of galaxies: Virgo (Lieu et al., 1996a), Coma (Lieu et al., 1996b), Abell 1795, Abell 2199, and Abell 4038. These results were obtained with the Deep Survey Telescope of the Extreme Ultraviolet Explorer (Bowyer and Malina, 1991) using a Lex/B filter which covers the 60 to 170 Å band. The extent of this diffuse emission from these clusters ranges from 20’ to 40’ in diameter. The statistical significance of these results varies from 8 to 50 standard deviations. Some EUV emission would be expected from the low-energy tail of the well-studied X-ray cluster emission. However, the EUV emission detected is far greater than the expected emission from the X-ray-emitting gas. Marginal signatures of this “soft excess” are often present in the lowest energy resolution band of the ROSAT PSPC where it is typically less than a 20% effect. In the case of Abell 2199, no low energy excess is present in the ROSAT data. In the data taken with EUVE, however, the excesses range from 70% to 600%.