Transients from initial conditions in cosmological simulations
Abstract
We study the impact of setting initial conditions in numerical simulations using the standard procedure based on the Zel'dovich approximation (ZA). As it is well known from the perturbation theory, ZA initial conditions have incorrect second and higherorder growth and therefore excite longlived transients in the evolution of the statistical properties of density and velocity fields. We also study the improvement brought by using more accurate initial conditions based on secondorder Lagrangian perturbation theory (2LPT). We show that 2LPT initial conditions reduce transients significantly and thus are much more appropriate for numerical simulations devoted to precision cosmology. Using controlled numerical experiments with ZA and 2LPT initial conditions, we show that simulations started at redshift z_{i} = 49 using the ZA underestimate the power spectrum in the nonlinear regime by about 2,4 and8per cent at z = 0,1, and3, respectively, whereas the mass function of dark matter haloes is underestimated by 5 per cent at m = 10^{15}M_{solar}h^{1} (z = 0) and 10 per cent at m = 2 × 10^{14}M_{solar}h^{1} (z = 1). The clustering of haloes is also affected to the few per cent level at z = 0. These systematics effects are typically larger than statistical uncertainties in recent mass function and power spectrum fitting formulae extracted from numerical simulations. At large scales, the measured transients in higherorder correlations can be understood from first principle calculations based on perturbation theory.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 2006
 DOI:
 10.1111/j.13652966.2006.11040.x
 arXiv:
 arXiv:astroph/0606505
 Bibcode:
 2006MNRAS.373..369C
 Keywords:

 methods: numerical;
 largescale structure of Universe;
 Astrophysics
 EPrint:
 14 pages, 14 figures, code to generate 2LPT initial conditions available at http://cosmo.nyu.edu/roman/2LPT . Typos corrected, Fig.13 symbols consistent with Fig.11,12