N-body simulations of galaxy clustering. I - Initial conditions and galaxy collapse times

N-body simulations of galaxy clustering in an expanding universe are described which typically start with 1000 point masses (representing galaxies) in initially random distributions and participating in the Hubble flow. In these simulations, small density fluctuations grow via gravitational instability, some eventually collapse to form bound clusters, and after sufficient time has elapsed, the model's galaxies are clustered in a manner similar to that observed in the real universe. The question of whether the observed distribution of glaxies can be effectively explained by the simple gravitational-instability picture is considered, and the sensitivity of the clustering to initial conditions is evaluated. The clusterings in simulations with the cosmological density parameter (Omega) equal to unity and 0.1 are compared. A typical collapse time of about 2 to 3 billion years is estimated for the galaxies and shown to be in agreement with other lines of evidence.