Statistical properties of filaments in the cosmic web

TL;DR

This study analyzes the statistical properties of cosmic web filaments using simulations, revealing how parameters like smoothing length and density thresholds influence filament length, density profiles, and cosmic web classifications.

Contribution

It introduces a detailed analysis of filament length distributions and density profiles in the cosmic web, highlighting the effects of key parameters on filament characteristics.

Findings

Filament volume fractions depend strongly on the threshold parameter $\lambda_{th}$.

Median filament lengths increase with larger smoothing lengths.

Radial density profiles show a valley at about twice the smoothing length, with shorter filaments being denser.

Abstract

In the context of the cosmological and constrained ELUCID simulation, this study explores the statistical characteristics of filaments within the cosmic web, focussing on aspects such as the distribution of filament lengths and their radial density profiles. Using the classification of the cosmic web environment through the Hessian matrix of the density field, our primary focus is on how cosmic structures react to the two variables $R_{\rm s}$ and $\lambda_{\rm th}$. The findings show that the volume fractions of knots, filaments, sheets, and voids are highly influenced by the threshold parameter $\lambda_{\rm th}$, with only a slight influence from the smoothing length $R_{\rm s}$. The central axis of the cylindrical filament is pinpointed using the medial-axis thinning algorithm of the COWS method. It is observed that median filament lengths tend to increase as the smoothing lengths increase. Analysis of filament length functions at different values of $R_{\rm s}$ indicates a reduction in shorter filaments and an increase in longer filaments as $R_{\rm s}$ increases, peaking around $2.5R_{\rm s}$. The study also shows that the radial density profiles of filaments are markedly affected by the parameters $R_{\rm s}$ and $\lambda_{\rm th}$, showing a valley at approximately $2R_{\rm s}$, with increases in the threshold leading to higher amplitudes of the density profile. Moreover, shorter filaments tend to have denser profiles than their longer counterparts.