Stable clustering and the resolution of dissipationless cosmological Nbody simulations
Abstract
The determination of the resolution of cosmological Nbody simulations, I.e. the range of scales in which quantities measured in them represent accurately the continuum limit, is an important open question. We address it here using scalefree models, for which selfsimilarity provides a powerful tool to control resolution. Such models also provide a robust testing ground for the socalled stable clustering approximation, which gives simple predictions for them. Studying large Nbody simulations of such models with different force smoothing, we find that these two issues are in fact very closely related: our conclusion is that the accuracy of twopoint statistics in the nonlinear regime starts to degrade strongly around the scale at which their behaviour deviates from that predicted by the stable clustering hypothesis. Physically the association of the two scales is in fact simple to understand: stable clustering fails to be a good approximation when there are strong interactions of structures (in particular merging) and it is precisely such nonlinear processes which are sensitive to fluctuations at the smaller scales affected by discretization. Resolution may be further degraded if the short distance gravitational smoothing scale is larger than the scale to which stable clustering can propagate. We examine in detail the very different conclusions of studies by Smith et al. and Widrow et al. and find that the strong deviations from stable clustering reported by these works are the results of overoptimistic assumptions about scales resolved accurately by the measured power spectra, and the reliance on Fourier space analysis. We emphasize the much poorer resolution obtained with the power spectrum compared to the twopoint correlation function.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2017
 DOI:
 10.1093/mnras/stx1356
 arXiv:
 arXiv:1609.04580
 Bibcode:
 2017MNRAS.470.4099B
 Keywords:

 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 15 pages, 5 figures, revised version published in MNRAS