# Proper Motions of the Satellites of M31

## TL;DR

This paper predicts proper motions for 19 M31 satellite galaxies to explain the stability of the satellite plane, independent of formation history, and discusses future measurement prospects with upcoming space missions.

## Contribution

It provides the first purely kinematic predictions of satellite proper motions to explain the M31 satellite plane stability.

## Key findings

- Predicted proper motion ranges for satellites.
- The satellite plane's stability can be explained by specific proper motions.
- Future missions like THEIA, HST, and JWST could measure these motions.

## Abstract

We predict the range of proper motions of 19 satellite galaxies of M31 that would rotationally stabilise the M31 plane of satellites consisting of 15-20 members as identified by Ibata et al. (2013). Our prediction is based purely on the current positions and line-of-sight velocities of these satellites and the assumption that the plane is not a transient feature. These predictions are therefore independent of the current debate about the formation history of this plane. We further comment on the feasibility of measuring these proper motions with future observations by the THEIA satellite mission as well as the currently planned observations by HST and JWST.