Statistical properties of filaments in the cosmic web

In the context of the cosmological and constrained Exploring the Local Universe with the reConstructed Initial Density field (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 Rₛ and λ ₜₕ. The findings show that the volume fractions of knots, filaments, sheets, and voids are highly influenced by the threshold parameter λ ₜₕ, with only a slight influence from the smoothing length Rₛ. The central axis of the cylindrical filament is pinpointed using the medial-axis thinning algorithm of the COsmic Web Skeleton (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 Rₛ indicates a reduction in shorter filaments and an increase in longer filaments as Rₛ increases, peaking around 2.5Rₛ. The study also shows that the radial density profiles of filaments are markedly affected by the parameters Rₛ and λ ₜₕ, showing a valley at approximately 2Rₛ, 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.