N-BODY SIMULATION OF LARGE-SCALE STRUCTURES IN LAMBDA-NOT-EQUAL-FRIEDMANN MODELS

This paper presents a study of the formation and evolution of large-scale structures in Friedmann models with a positive cosmological constant LAMBDA. The goal is to find out if current observations either support or rule out the existence of LAMBDA and to suggest observational tests that could answer the question. A series of 18 N-body simulations were carried out, for four different Friedmann models: OMEGA-0 = 1, lambda-0 = 0 (four calculations), OMEGA-0 = 0.2, lambda-0 = 0 (five calculations), OMEGA-0 = 0.2, lambda-0 = 0.8 (five calculations), and OMEGA-0 = 0.2, H0t0 = 2 (four calculations). All simulations were done using a P3M algorithm with 32,768 particles. The initial conditions were set up in order to reproduce the linear growing mode of a standard cold dark matter fluctuation spectrum. Biased galaxy formation is implemented into the algorithm using an original technique based on physical considerations on the density and density contrast around particles. In all calculations, galaxy clustering proceeds rapidly, leading to the formation of massive clusters connected by bridges and surrounding vast underdense regions. Several aspects of the final states are compared among the various models, with observations, and with results of simulations carried out by previous authors. The final positions of the particles are very similar in all models, and consequently all results based on these positions only [morphology and topology of the final configurations, two-point correlation function xi(r), and angular two-point correlation function w(theta)[ are essentially independent of the cosmological constant. Since the peculiar velocity field varies among the various models, results involving the final velocities of the particles might show a dependence on LAMBDA. However, the moments of the relative peculiar velocity between pairs turn out to depend upon OMEGA-0, but not lambda-0. Similarly, the galaxy distribution in "slices", and the number counts in redshift space, which both depend upon the Hubble distance of galaxies to the observer, show very little dependence on LAMBDA. The only results which are sensitive to the presence of the cosmological constant are the rate of galaxy formation, and the buildup of angular momentum in clusters by merging events. The former result imposes a strong constraint on any phenomenological biasing scheme: the presence of a large cosmological constant inhibits galaxy formation by increasing significantly the minimum density required for a clump to collapse. The later result suggests an observational test: the search for clusters of galaxies with low net angular momentum.