Bar-Halo Friction in Galaxies III: Particle Number Requirements for Simulations

TL;DR

This study investigates the particle number requirements in N-body simulations of dark matter halo interactions with galactic bars, finding that standard particle counts are sufficient and challenging previous claims of the need for extremely high particle numbers.

Contribution

The paper demonstrates that typical N-body simulation particle numbers are adequate for modeling bar-halo interactions, countering prior assertions that much higher counts are necessary.

Findings

Simulation results show no dependence on particle number within standard ranges.

Field and grid methods yield similar results, confirming robustness.

The suggested high particle number by Weinberg & Katz is unnecessary.

Abstract

The question whether the dark matter halo density in the centers of galaxies could be changed through interactions with a rotating bar in the baryonic disk is of considerable current interest. While N-body simulations have been used to address this question, it has also been claimed that results from such simulations cannot be trusted. Based on a perturbative treatment of resonant exchanges between orbits and a rotating perturbation, Weinberg & Katz contend that N-body simulations of this process will not reveal the continuum result unless many more than the usual numbers of particles are employed. Here I report a study designed to examine their contention, finding results that show no dependence on the number of particles over the range usually employed up to that advocated by these authors. I show that my results are independent of all numerical parameters, and that field methods perform equally with grid methods in this respect. I also identify the reasons that the required particle number suggested by Weinberg & Katz is excessive.