Mass-to-light ratio of galaxy systems

We study the mass-to-light ratio of galaxy systems from poor groups to rich clusters. We extend a previous work based on 89 clusters obtaining blue luminosity and virial mass for other 52 clusters, 43 poor systems, and similar to 500 groups of two catalogs. A large effort is devoted to the homogeneity of the resulting values. Analyzing a combined sample of 294 systems we find that mass increases faster than the luminosity does: the linear fit gives M proportional to L(B)(1.34+/-0.03), and we find a tendency for a steeper increase in the low-mass range. We compare our results to the behavior of M/L(B) vs. halo mass as predicted by cosmological numerical simulations coupled with semianalytic modeling of galaxy formation.