How universal are the density profiles of dark halos?

We use high-resolution N-body simulations to investigate the formation of v irialized halos due to the gravitational collapse of collisionless matter. A variety of formation scenarios are studied, ranging from hierarchical clu stering to monolithic radial collapse. The goal of these experiments was to study departures from the universal density profiles recently found to ari se in cosmological settings. However, we found that even for models that ex hibit quite a different formation history, the density and velocity dispers ion profiles of the virialized halos are strikingly similar. Power-law density profiles do not result even in models with initial power- law profiles and without initial substructure or nonradial motions. Such in itial conditions give rise to a radial orbit instability that leads to curv ed velocity dispersion and density profiles. The shapes of the density prof iles in all our models are well parameterized by the profiles of halos form ed in a generic cosmological setting. Our results show that the universalit y of dark halo density profiles does not depend crucially on hierarchical m erging as has been suggested recently in the literature. Rather it arises b ecause apparently different collapse histories produce a near universal ang ular momentum distribution among the halo particles. We conclude that the g eneral form of the density and velocity dispersion profiles of virialized h alos in an expanding universe are robust outcomes of gravitational collapse , nearly independent of the initial conditions and the formation history.