Anisotropic satellite accretion onto the Local Group with HESTIA

TL;DR

This study investigates how the cosmic web influences satellite galaxy accretion onto the Local Group, revealing a strong alignment of infall directions with the cosmic web's structure, especially during early accretion phases.

Contribution

It demonstrates the connection between satellite infall directions and the cosmic web's anisotropic structure using constrained simulations of the Local Group.

Findings

Satellites can travel up to ~4 Mpc before crossing the virial radius.

Strong alignment of satellite infall with the slowest collapse axis of the cosmic web.

Two distinct accretion eras identified, separated by redshift z ≈ 0.7.

Abstract

How the cosmic web feeds halos, and fuels galaxy formation is an open question with wide implications. This study explores the mass assembly in the Local Group within the context of the local cosmography by employing simulations whose initial conditions have been constrained to reproduce the local environment. The goal of this study is to inspect whether the direction of accretion of satellites on to the Milky Way and Andromeda galaxies, is related to the cosmic web. The analysis considers the three high-resolution simulations available in the HESTIA simulation suite, as well as the derived velocity shear and tidal tensors. We notice two eras in the Local Group accretion history, delimited by an epoch around $z \approx 0.7$. We also find that satellites can travel up to $\sim 4$ Mpc, relative to their parent halo before crossing its viral radius $R_{200}$. Finally, we observe a strong alignment of the infall direction with the axis of slowest collapse $\vec{e_3}$ of both tidal and shear tensors, implying satellites of the Local Group originated from one particular region of the cosmic web and were channeled towards us via the process of accretion.This alignment is dominated by the satellites that enter during the early infall era, i.e $z>0.7$.