SCF-FDPS: A Fast N-body Code for Simulating Disk-Halo Systems

A fast N-body code has been developed for simulating a stellar disk embedded in a live dark matter halo. In generating its Poisson solver, a self-consistent field (SCF) code that inherently possesses perfect scalability is incorporated into a tree code that is parallelized using a library termed Framework for Developing Particle Simulators (FDPS). Thus, the code developed here is called SCF-FDPS. This code has realized the speedup of a conventional tree code by applying an SCF method not only to the calculation of the self-gravity of the halo but also to that of the gravitational interactions between the disk and halo particles. Consequently, in the SCF-FDPS code, a tree algorithm is applied only to calculate the self-gravity of the disk. On a many-core parallel computer, the SCF-FDPS code has performed at least 3 times (in one case, nearly an order of magnitude) faster than an extremely tuned tree code on it, if the numbers of disk and halo particles are, respectively, fixed for both codes. In addition, the SCF-FDPS code shows that the central processing unit cost scales almost linearly with the total number of particles and almost inversely with the number of cores. We find that the time evolution of a disk-halo system simulated with the SCF-FDPS code is, in large measure, similar to that obtained using the tree code. We suggest how the present code can be extended to cope with a wide variety of disk-galaxy simulations.

Automated summary

A fast N-body code, SCF-FDPS, has been developed to simulate a stellar disk embedded in a live dark matter halo. The code combines a self-consistent field (SCF) code with a parallelized tree code using the Framework for Developing Particle Simulators (FDPS) library. The SCF-FDPS code calculates the self-gravity of the halo and the gravitational interactions between the disk and halo particles. It achieves a speedup of at least 3 times compared to a tuned tree code, and its central processing unit cost scales almost linearly with the total number of particles.