ROSAT Results on Groups and Clusters of Galaxies

Abstract

We present a selection of ROSAT results on the morphology, the evolution, and the masses of galaxy clusters and groups. ROSAT provides the first complete X-ray view on the Virgo cluster: it reveals a complex structure similar to the optical appearance. Indications for ongoing evolution is found in a number of clusters traced both by the surface brightness distribution and temperature variations. With ROSAT data, which provide spatial and spectral resolution at the same time, good mass estimates can be obtained for various systems from small groups to very massive clusters covering a mass range of a few $10^{13}$ to $4.6\cdot10^{15}\msol$. The gas to dark matter ratio for clusters is 10-30\% while for groups slightly smaller values (3-25\%) are found. The most luminous ROSAT cluster RXJ1347.5-1145 is presented which is an ideal object to compare the X-ray mass with the mass derived by gravitational lensing.