SUPERBOX - an efficient code for collisionless galactic dynamics

We present SUPERBOX, a particle-mesh code with high resolution sub-grids an d an NGP (nearest grid point) force-calculation scheme based on the second derivatives of the potential. SUPERBOX implements a fast low-storage FFT-al gorithm, giving the possibility to work with millions of particles on desk- top computers. Test calculations show energy and angular momentum conservat ion to one part in 10(5) per crossing-time. The effects of grid and numeric al relaxation remain negligible, even when these calculations cover a Hubbl e-time of evolution. As the sub-grids follow the trajectories of individual galaxies, the code allows a highly resolved treatment of interactions in c lusters of galaxies, such as high-velocity encounters between elliptical ga laxies and the tidal disruption of dwarf galaxies. Excellent agreement is o btained in a comparison with a direct-summation N-body code running on spec ial-purpose GRAPE 3 hardware. The orbital decay of satellite galaxies due t o dynamical friction obtained with SUPERBOX agrees with Chandrasekhar's tre atment when the Coulomb logarithm ln Lambda approximate to 1.5. (C) 2000 El sevier Science B. V. All rights reserved.