Second-order Lagrangian perturbation theory initial conditions for resimulations

TL;DR

This paper introduces a second-order Lagrangian perturbation theory method for generating initial conditions in cosmological N-body simulations, improving accuracy and efficiency especially for resimulations of structure formation.

Contribution

The authors develop and validate a 2lpt-based method for initial conditions that enhances accuracy for resimulations and reduces the need for early start redshifts compared to Zel'dovich.

Findings

2lpt initial conditions improve accuracy in structure formation simulations.

Simulations with 2lpt start later, saving computational resources.

Delay in structure formation with Zel'dovich initial conditions can be corrected using spherical collapse model.

Abstract

We describe and test a new method for creating initial conditions for cosmological N-body dark matter simulations based on second-order Lagrangian perturbation theory (2lpt). The method can be applied to multi-mass particle distributions making it suitable for creating resimulation, or `zoom' initial conditions. By testing against an analytic solution we show that the method works well for a spherically symmetric perturbation with radial features ranging over more than three orders of magnitude in linear scale and eleven orders of magnitude in particle mass. We apply the method and repeat resimulations of the rapid formation of a high mass halo at redshift fifty and the formation of a Milky-Way mass dark matter halo at redshift zero. In both cases we find that many properties of the final halo show a much smaller sensitivity to the start redshift with the 2lpt initial conditions, than simulations started from Zel'dovich initial conditions. For spherical overdense regions structure formation is erroneously delayed in simulations starting from Zel'dovich initial conditions, and we demonstrate for the case of the formation the high redshift halo that this delay can be accounted for using the spherical collapse model. In addition to being more accurate, 2lpt initial conditions allow simulations to start later, saving computer time.