A new hierachical particle-mesh code for very large scale cosmological N-body simulations

Abstract

An improved three-dimensional hierarchical particle-mesh (HPM) N-body code for the gravitational evolution of structure in the universe has been developed and tested. The basis of the code is a standard particle-mesh (PM) code where Poisson's equation is solved on a critical grid with fast Fourier transform techniques and periodic boundary conditions. Several subgrids and father grids can fit into a cube. The fields from the father grid, and its father grid, and so on, are treated as external fields. There is no back-reaction to father grids, and particles can enter and exit subgrids. In a four grid code the dynamic range can be extended to 6000 in length and 11 orders of magnitude in mass. The initial conditions are generated with a random phase realization of the power spectrum of the growing mode using the Zel'dovich approximation (1970). The HPM code is much faster than tree codes and particle-particle-mesh codes, and has a much larger dynamic range. 28 refs.