XMM-Newton Discovery of O VII Emission from Warm Gas in Clusters of Galaxies

XMM-Newton recently discovered O VII line emission from ~ 2 million K gas near the outer parts of several clusters of galaxies. This emission is attributed to the Warm-Hot Intergalactic Medium. The original sample of clusters studied for this purpose has been extended and two more clusters with a soft X-ray excess have been found. We discuss the physical properties of the warm gas, in particular the density, spatial extent, abundances and temperature.