Dissipationless collapse in an expanding universe

The formation and equilibrium characteristics of systems formed through dissipationless collapse are studied. Initially, the systems are isolated, spherically symmetric top hats in solid body rotation and in Hubble flow. Small-scale power is added using the Zel'dovich approximation assuming a power-law slope and including velocities self-consistently. Simulations are run for two different values of the power-law slope: n = 0 and n = - 2. 5. The initial conditions are more general than past simulations of isolated systems and are chosen to be more cosmologically relevant in an effort to connect simulations involving the collapse of isolated perturbations with those extracted from larger cosmological simulations. With these initial conditions collapses are clumpy and resemble multiple merger events. The final density profiles in projection approximately follow a de Vaucouleurs R¹/4^ law. The radial orbit instability does not appear important in determining the final shape of the systems. These shapes range from oblate to triaxial to prolate. With these more general initial conditions the initial T/W does not completely determine the final equilibrium state. The equilibrium systems are slowly rotating, with a measured flat rotation curve, and are supported by an anisotropic velocity dispersion. The final equilibria closely resemble elliptical galaxies with projected ellipticities ranging from E1 to E6. This lends support to the theory that elliptical galaxies formed through dissipationless collapse. These models could also represent formation of galactic halos and give new insights into the central structure of dark halos.