Vast planes of satellites in a high resolution simulation of the Local Group: comparison to Andromeda

TL;DR

This study uses high-resolution simulations of the Local Group to identify and analyze vast planes of satellites, comparing their properties to the observed plane around Andromeda, revealing similarities and differences.

Contribution

It introduces a simple detection method for satellite planes in high-res simulations and compares simulated structures to the observed plane of M31.

Findings

Simulated satellite planes are predominantly co-rotating and non-random.

The observed M31 plane is slightly richer, thinner, and more co-rotating than simulated ones.

Simulated planes are often fortuitous and not fully kinematically coherent.

Abstract

We search for vast planes of satellites (VPoS) in a high resolution simulation of the Local Group performed by the CLUES project, which improves significantly the resolution of former similar studies. We use a simple method for detecting planar configurations of satellites, and validate it on the known plane of M31. We implement a range of prescriptions for modelling the satellite populations, roughly reproducing the variety of recipes used in the literature, and investigate the occurence and properties of planar structures in these populations. The structure of the simulated satellite systems is strongly non-random and contains planes of satellites, predominantly co-rotating, with, in some cases, sizes comparable to the plane observed in M31 by Ibata et al.. However the latter is slightly richer in satellites, slightly thinner and has stronger co-rotation, which makes it stand out as overall more exceptional than the simulated planes, when compared to a random population. Although the simulated planes we find are generally dominated by one real structure, forming its backbone, they are also partly fortuitous and are thus not kinematically coherent structures as a whole. Provided that the simulated and observed planes of satellites are indeed of the same nature, our results suggest that the VPoS of M31 is not a coherent disc and that one third to one half of its satellites must have large proper motions perpendicular to the plane.