The mean luminosity and mass densities in the Universe

The contribution of matter associated with galaxies to the critical mass-density ratio of the Universe is reevaluated using a more complete and homogeneous data set than previously employed. The characteristic M/L ratio of galaxies and the mean luminosity in the Universe are computed taking account of possible contributions from massive halos to the former and the local supercluster to the latter. The best estimates obtained are 47 million times the solar luminosity per cu Mpc for the mean luminosity, a characteristic M/L ratio that is 120 times the solar value, and a galactic matter contribution of 0.08 to the critical mass-density ratio. It is shown that the statistical uncertainties in the galactic matter contribution probably do not exceed 50% and that the data nearly exclude a contribution of unity or more. It is concluded that if the Friedmann world model with a cosmological constant of zero applies and if galaxies and their environs contain more than a small fraction of all matter, then the Universe is open by a wide margin.