What can Gaia proper motions tell us about Milky Way dwarf galaxies?

TL;DR

This study assesses Gaia's potential to measure the systemic proper motion of the Sculptor dwarf galaxy, demonstrating that accurate motion recovery is feasible despite measurement uncertainties.

Contribution

It provides a model-based analysis of Gaia's proper-motion accuracy for dwarf galaxies, specifically showing the recoverability of Sculptor's systemic motion at 79 kpc.

Findings

Gaia can measure proper motions of hundreds of stars in Sculptor.

Systemic proper motion can be recovered despite measurement uncertainties.

Proper motions of ~10 mas/century are sufficient for systemic motion detection.

Abstract

We present a proper-motion study on models of the dwarf spheroidal galaxy Sculptor, based on the predicted proper-motion accuracy of Gaia measurements. Gaia will measure proper motions of several hundreds of stars for a Sculptor-like system. Even with an uncertainty on the proper motion of order 1.5 times the size of an individual proper-motion value of ~10 mas/century, we find that it is possible to recover Sculptor's systemic proper motion at its distance of 79 kpc.