Particle number dependence in the nonlinear evolution of Nbody selfgravitating systems
Abstract
Simulations of purely selfgravitating Nbody systems are often used in astrophysics and cosmology to study the collisionless limit of such systems. Their results for macroscopic quantities should then converge well for sufficiently large N. Using a study of the evolution from a simple space of spherical initial conditions  including a region characterized by socalled 'radial orbit instability'  we illustrate that the values of N at which such convergence is obtained can vary enormously. In the family of initial conditions we study, good convergence can be obtained up to a few dynamical times with N ˜ 10^{3}  just large enough to suppress two body relaxation  for certain initial conditions, while in other cases such convergence is not attained at this time even in our largest simulations with N ˜ 10^{5}. The qualitative difference is due to the stability properties of fluctuations introduced by the Nbody discretisation, of which the initial amplitude depends on N. We discuss briefly why the crucial role which such fluctuations can potentially play in the evolution of the N body system could, in particular, constitute a serious problem in cosmological simulations of dark matter.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 2018
 DOI:
 10.1093/mnras/stx2444
 arXiv:
 arXiv:1709.06657
 Bibcode:
 2018MNRAS.473.2348B
 Keywords:

 methods: numerical;
 galaxies: elliptical and lenticular;
 cD;
 galaxies: formation;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 8 pages, 5 figures