The place of the Local Group in the cosmic web

TL;DR

This study uses simulations to determine the typical location and orientation of the Local Group within the cosmic web, revealing its preference for filamentary and sheet environments and specific alignments with the web's structure.

Contribution

It introduces a method to identify the Local Group's probable cosmic web environment and analyzes its orientation and alignment using the Bolshoi Simulation.

Findings

The Local Group prefers filament and sheet environments.

LG's orbital angular momentum is perpendicular to the smallest tidal eigenvector.

The pair's connecting vector aligns with the smallest tidal eigenvector.

Abstract

We use the Bolshoi Simulation to find the most probable location of the Local Group (LG) in the cosmic web. Our LG simulacra are pairs of halos with isolation and kinematic properties consistent with observations. The cosmic web is defined using a tidal tensor approach. We find that the LG's preferred location is regions with a dark matter overdensity close to the cosmic average. This makes filaments and sheets the preferred environment. We also find a strong alignment between the LG and the cosmic web. The orbital angular momentum is preferentially perpendicular to the smallest tidal eigenvector, while the vector connecting the two halos is strongly aligned along the smallest tidal eigenvector and perpendicular to the largest tidal eigenvector; the pair lies and moves along filaments and sheets. We do not find any evidence for an alignment between the spin of each halo in the pair and the cosmic web.