The geometry of the filamentary environment of galaxy clusters

TL;DR

This study maps the filamentary structures around galaxy clusters in simulations, revealing their orientations, mass distributions, and how observational measurements are affected by these structures.

Contribution

It introduces an extended filament finder to analyze the geometry and properties of filaments around clusters, highlighting their alignment and impact on observational scatter.

Findings

Filaments often have endpoints outside sheets with alignments perpendicular to the plane.

Cluster long axes tend to lie within sheets and their orientation correlates with mass measurement scatter.

Observational scatter varies with the line of sight relative to local sheets and filaments.

Abstract

We construct a filament catalogue using an extension of the halo based filament finder of Zhang et al.(2009), in a 250 Mpc/h side N-body simulation, and study the properties of filaments ending upon or surrounding galaxy clusters (within 10 Mpc/h). In this region, the majority of filamentary mass, halo mass, and galaxy richness centered upon the cluster tends to lie in sheets, which are not always coincident. Fixing a sheet width of 3 Mpc/h for definiteness, we find the sheet orientations and (connected) filamentary mass, halo mass and richness fractions relative to the surrounding sphere. Filaments usually have one or more endpoints outside the sheet determined by filament or halo mass or richness, with at least one having a large probability to be aligned with the perpendicular of the plane. Scatter in mock cluster mass measurements, for several observables, is often correlated with the observational direction relative to these local sheets, most often for richness and weak lensing, somewhat less for Compton decrement, and least often for velocity dispersions. The long axis of the cluster also tends to lie in the sheet andits orientiation relative to line of sight also correlates with mass scatter.