Optical mass estimates of galaxy clusters

We evaluate in a homogeneous way the optical masses of 170 nearby dusters ( z less than or equal to 0.15). The sample includes both data from the liter ature and the new ESO Nearby Abell Clusters Survey (ENACS) data. On the ass umption that mass follows the galaxy distribution, we compute the mass of e ach cluster by applying the virial theorem to the member galaxies. We const rain the masses of very substructured clusters (about 10% of our clusters) between two limiting values. After appropriate rescaling to the X-ray radii , we compare our optical mass estimates to those derived from X-ray analyse s, which we compiled from the literature (for 66 clusters). We find a good overall agreement. This agreement is expected in the framework of two commo n assumptions: that mass follows the galaxy distribution and that clusters are not far from a situation of dynamical equilibrium, with both gas and ga laxies reflecting the same underlying mass distribution. We stress that our study strongly supports the reliability of present cluster mass estimates derived from X-ray analyses and/or (appropriate) optical analyses.