Mass and Metallicity of Five X‐Ray–bright Galaxy Groups

We present ASCA X-ray observations of a sample of five groups selected from across-correlation of the ROSAT All-Sky Survey with the White et al. opticalcatalog of groups. These X-ray bright groups significantly increase the numberof known systems with temperatures between 2 and 3 keV. They have elementabundances of roughly 0.3 times solar that are typical of clusters, but theirfavored ratio of Si/Fe abundance is lower than the cluster value. Combining theASCA results with ROSAT imaging data, we calculate total masses of a few toseveral times 10^13 M_sun, gas mass fractions of ~10%, and baryonic massfractions of at least 15-20% within a radius of 0.5 Mpc. Upper limits for theratios of gas to galaxy mass and of the iron mass to galaxy luminosity overlapwith the range observed in rich clusters and extend to lower values, but not tosuch low values as seen in much poorer groups. These results support the ideathat groups, unlike clusters, are subject to the loss of their primordial andprocessed gas, and show that this transition occurs at the mass scale of the2-3 keV groups. A discussion of ASCA calibration issues and a comparison ofROSAT and ASCA temperatures are included in an Appendix.