Why Cosmic Voids Matter: Nonlinear Structure & Linear Dynamics

TL;DR

This study uses advanced hydrodynamical simulations to analyze cosmic voids, revealing their universal properties and demonstrating that tracer motions around voids follow linear dynamics, making voids excellent probes for cosmology.

Contribution

The paper provides a comprehensive analysis of void properties across different resolutions and tracer types, highlighting their universal characteristics and linear behavior.

Findings

Void properties are largely independent of tracer type and resolution.

Tracer motions around void centers are consistent with linear dynamics.

Void regions show no signs of nonlinear dynamics even at small scales.

Abstract

We use the Magneticum suite of state-of-the-art hydrodynamical simulations to identify cosmic voids based on the watershed technique and investigate their most fundamental properties across different resolutions in mass and scale. This encompasses the distributions of void sizes, shapes, and content, as well as their radial density and velocity profiles traced by the distribution of cold dark matter particles and halos. We also study the impact of various tracer properties, such as their sparsity and mass, and the influence of void merging on these summary statistics. Our results reveal that all of the analyzed void properties are physically related to each other and describe universal characteristics that are largely independent of tracer type and resolution. Most notably, we find that the motion of tracers around void centers is perfectly consistent with linear dynamics, both for individual, as well as stacked voids. Despite the large range of scales accessible in our simulations, we are unable to identify the occurrence of nonlinear dynamics even inside voids of only a few Mpc in size. This suggests voids to be among the most pristine probes of cosmology down to scales that are commonly referred to as highly nonlinear in the field of large-scale structure.