Evolution of isolated overdensities as a control on cosmological N body simulations

Understand

Beyond convergence studies and comparison of different codes, there are essentially no controls on the accuracy in the non-linear regime of cosmological N body simulations, even in the dissipationless limit.

• We propose and explore here a simple test which has not been previously employed: when cosmological codes are used to simulate an isolated overdensity, they should reproduce, in physical coordinates, those obtained in open boundary conditions without expansion.
• In particular, the desired collisionless nature of the simulations can be probed by testing for stability in physical coordinates of virialized equilibria.
• We investigate and illustrate the test using a suite of simulations in an Einstein de Sitter cosmology from initial conditions which rapidly settle to virial equilibrium.