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We investigate a sample of 14 clusters of galaxies observed with XMM-Newtonin a search for soft X-ray excess emission. In five of these clusters asignificant soft excess is evident. This soft X-ray excess is compared with thethermal emission from both the hot intracluster gas and any cooling (flow) gasthat may be present. A warm (kT=0.2 keV), extended (several Mpc), plasmacomponent is particularly clear in the outer parts of the cluster, where thenormal cluster X-ray emission is weak. This warm component causes both athermal soft X-ray excess at low energies (below 0.4-0.5 keV), as well as O VIIline emission with a redshift consistent with a cluster origin, and not easilyinterpreted as Galactic foreground emission. The intensity of this component iscommensurate with what has been measured before with the ROSAT PSPC in the 1/4keV band. We attribute this component to emission from intercluster filamentsof the Warm-Hot Intergalactic Medium in the vicinity of these clusters. For thecentral regions of clusters the detection of lines in the soft X-ray spectrumis more difficult, due to the predominance of the X-ray emitting hot plasmathere, hence we cannot discriminate between the thermal and nonthermal originof the soft excess, leaving several options open. These include thermalemission from warm filaments seen in projection in front of or behind thecluster center, thermal or nonthermal emission in the cluster core itselfrelated to magnetic reconnection, or Inverse Compton emission from the cosmicmicrowave background on relativistic electrons.Comment: 18 pages, 24 figures, accepted for publication in Astronomy and  Astrophysic

astronomy and astrophysics

XMM-Newton confirmation of soft X-ray excess emission in clusters of galaxies – The discovery of O VII emission from an extended warm baryonic component