EUV and soft X-rays from clusters of galaxies - the `cluster soft-excess' phenomenon

Clusters of galaxies are strong emitters of EUV and soft X-rays substantially in excess of the contribution from the hot intra-cluster medium at X-ray temperatures. After the initial discovery of EUV excess emission in the Virgo cluster, the phenomenon was reported also for the Coma, A1795 and A2199 clusters. Recent reobservations confirmed the finding, and further searches on a large sample of nearby galaxy clusters are clearly revealing the cosmological impact of the discovery.