The total baryon fraction in groups: mapping hot gas out to the virial radius

Galaxy groups contain the majority of galaxies, and probably most ofthe baryons, in the Universe. Unfortunately the low Xray surfacebrightness of groups has prevented the detection of the gas at largeradii which should dominate their baryon content. The superbsensitivity of XMM offers the first opportunity to remedy this. Wepropose, for the first time, to trace the surface brightness ofseveral groups out to their virial radii. This will allow us tomeasure total gas and iron masses, baryon fractions, and mass/light,gas/star and ironmass/light ratios, and to investigate the truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]