Dark matter and the dynamics of galaxy clustering

The dynamics of galaxy clustering is investigated in simulations of the large-scale structure of the universe. Emphasis is placed on determining the accuracy of virial mass estimates, and therefore of the mean mass density in the universe. For galaxies modeled as point masses, the virial theorem yields mass estimates accurate to within a factor of 2 for a wide range of clustered systems. The point mass approximation, however, is incapable of reproducing observed small scale clustering behavior, and is unrealistic in view of the observational and theoretical evidence for dominant amounts of dark matter around individual galaxies and in clusters. Simulations of the large-scale clustering of galaxies with massive dark halos are then performed for both a critically dense and open universe. The extended mass distribution and dynamical friction, both absent in the point mass models, conspire to reduce galactic peculiar velocities on clustered scales and enhance galaxy correlations at small separations. The median virial mass estimates of galaxy groups systematically underestimate the total mass present by at least a factor of 3