PROPERTIES OF GALACTIC HALOS IN SPATIALLY FLAT UNIVERSES DOMINATED BY COLD DARK MATTER - EFFECTS OF NONVANISHING COSMOLOGICAL CONSTANT

Properties of galactic halos in the cold dark matter (CDM) dominated universes are studied using cosmological N-body simulations. Assuming that the universe is spatially flat, we consider two specific examples in CDM cosmogonies; one is the Einstein-de Sitter model, and the other is given a low mean mass density and nonvanishing cosmological constant, A. The identification scheme of halos from the simulations is essential in discussing their properties, and we tried both a conventional friends-of-friends algorithm and a refinement of it to avoid the clouds-in-clouds problem. The resulting properties of halos prove to sensitively depend on the identification scheme and the adopted parameters. In particular, we find that flat rotation curve of halos extending approximately 100 h-1 kpc is reproduced only with the fixed-linking friends-of-friends algorithm for the CDM models in the Einstein-de Sitter universe. Thus such a shape of the rotation curve may not be a universal feature intrinsic to the models. Models with nonzero-lambda, on the other hand, show nearly flat rotation curves up to approximately (50-100) h-1 kpc. In addition, this conclusion is relatively insensitive to the halo identification algorithm in contrast to the case with the Einstein-de Sitter models. Therefore nonzero-lambda CDM models most successfully account for the observed flat rotation curve of galaxies.