Observed dynamics of superclusters

Abstract

Radial velocity measurements of two large, rich superclusters show evidence of a gravitational slowing of the Hubble flow within the superclusters. Models assuming spherically symmetric, noncrossing mass shells yield mass density estimates for the clusters ranging from less than one to several times the critical density, and preliminary counts of galaxies and Abell clusters indicate a density enhancement within the superclusters of 10-71 times the field mass density. The combination of these two results is found to favor an open universe, assuming a standard Friedmann cosmology. It is noted that all forms of mass that are clumped on the scale of superclusters, or smaller, will be detected by these measurements, including neutrinos sufficiently massive to significantly contribute to the cosmological density parameter.