The Generation of Vorticity in Cosmological N-body Simulations

TL;DR

This paper investigates how vorticity is generated in the universe's large-scale structure through collisionless dark matter dynamics, using relativistic N-body simulations to analyze vorticity power spectra and their evolution.

Contribution

It introduces methods to compute and analyze the vorticity power spectrum in cosmological simulations, highlighting the role of shell crossing and velocity dispersion in vorticity generation.

Findings

Vorticity is generated during structure formation due to shell crossing.

The vorticity power spectrum's shape and amplitude evolve over time.

Simulation results are consistent with previous studies and show convergence with resolution.

Abstract

Clustering of a perfect fluid does not lead to the generation of vorticity. It is the collisionless nature of dark matter, inducing velocity dispersion and shell crossing, which is at the origin of cosmological vorticity generation. In this paper we investigate the generation of vorticity during the formation of cosmological large scale structure using the public relativistic N-body code $\textit{gevolution}$. We test several methods to compute the vorticity power spectrum and we study its convergence with respect to the mass and grid resolution of our simulations. We determine the power spectrum, the spectral index on large-scales, the amplitude of the peak position and their time evolution. We also compare the vorticity extracted from our simulations with the vector perturbations of the metric. Our results are accompanied by resolution studies and compared with previous studies in the literature.