Understanding the cosmic web

TL;DR

This paper studies the evolution of the cosmic web from redshift 2 to the present using the NEXUS+ algorithm, introducing new tools to analyze its hierarchical structure and the nature of voids.

Contribution

It introduces new analysis tools tailored for the cosmic web's complex hierarchy and characterizes filaments, walls, and voids in terms of their densities and boundaries.

Findings

Early universe dominated by tenuous filaments and sheets.

Web structures merge over time into fewer, more massive entities.

Void density profiles are universal when measured from their boundaries.

Abstract

We investigate the characteristics and the time evolution of the cosmic web from redshift, z=2, to present time, within the framework of the NEXUS+ algorithm. This necessitates the introduction of new analysis tools optimally suited to describe the very intricate and hierarchical pattern that is the cosmic web. In particular, we characterize filaments (walls) in terms of their linear (surface) mass density. This is very good in capturing the evolution of these structures. At early times the cosmos is dominated by tenuous filaments and sheets, which, during subsequent evolution, merge together, such that the present day web is dominated by fewer, but much more massive, structures. We also show that voids are more naturally described in terms of their boundaries and not their centres. We illustrate this for void density profiles, which, when expressed as a function of the distance from void boundary, show a universal profile in good qualitative agreement with the theoretical shell-crossing framework of expanding underdense regions.