Local Group analogues in a cosmological context -- I. Relating velocity structure to the cosmic web

TL;DR

This study investigates how the velocity structure of Local Group analogues relates to their large-scale cosmic environment using simulations, revealing correlations between orbital energy, density, and filament alignment.

Contribution

It introduces the coupling energy of the MW-M31 orbit as a key factor linking Local Group analogues to their cosmic web environment, providing new insights into their formation and structure.

Findings

High coupling energy LGAs are in denser regions.

Low coupling energy LGAs align with cosmic filaments.

The real Local Group has typical coupling energy and environment.

Abstract

Our Local Group, dominated in mass by the Milky Way (MW) and M31, provides a unique laboratory for testing $\Lambda$CDM cosmology on small scales owing to its proximity. However, its connection to the surrounding large-scale environment, which is essential for interpreting its properties, is inadequately understood. In this work, we explore the connection between Local Group analogues (LGAs) and their surrounding large-scale environments using the ABACUSSUMMIT simulation suite, highlighting the key role of the coupling energy of the MW-M31 orbit, $E_{\rm coupling}$. We find that LGAs with high $E_{\rm coupling}$ preferentially reside in denser regions, whereas those with low $E_{\rm coupling}$ tend to occupy low-density environments. Furthermore, LGAs with low $E_{\rm coupling}$ exhibit strong alignment with cosmic filaments, manifested as a pronounced polar anisotropy in the distribution of tracer haloes. By contrast, LGAs with high $E_{\rm coupling}$ show a weaker polar anisotropy but an enhanced azimuthal anisotropy, with large-scale tracer haloes preferentially lying in the plane spanned by the halo pair and the orbital spin vector. Within this framework, our Local Group is characterised by typical $E_{\rm coupling}$ residing in a relatively under-dense environment, yet it remains consistent with the 95\% range of analogue systems identified in the simulation.