Angular momentum from tidal torques

The authors describe results for the origin of angular momentum of bound objects in large cosmological N-body simulations. Three sets of models are analyzed: one with white-noise initial conditions and two in which the initial conditions have more power on large scales, as predicted in models with cold dark matter (CDM). Statistical analysis of large catalogs of objects shows that the dimensionless spin parameter λ is remarkably insensitive to the initial perturbation spectrum and has a median value λme≡ 0.05. The quantity λ is weakly correlated with mass and internal substructure and is uncorrelated with initial overdensity. In CDM models, groups with high λ-values tend to have nearer neighbors and are more strongly clustered than groups with low λ; these effects are weaker or absent in white-noise models.