Disassembling the Galaxy with angle-action coordinates

TL;DR

This paper demonstrates how angle-action coordinates can be used to identify and analyze relics of satellite galaxies in the Milky Way, enabling insights into Galactic potential and disruption history.

Contribution

It introduces a method to use angle-action coordinates for detecting satellite galaxy remnants and estimating their disruption times, even with approximate potentials.

Findings

Relics form identifiable patches in action space near the Sun.

Using correct potentials aligns the patches, while incorrect potentials displace them.

Angle coordinates can help determine the Galactic potential and the age of relics.

Abstract

Angle-action coordinates are used to study the relic of an N-body simulation of a self-gravitating satellite galaxy that was released on a short-period orbit within the disc of the Galaxy. Satellite stars that lie within 1.5 kpc of the Sun are confined to a grid of patches in action space. As the relic phase-mixes for longer, the patches become smaller and more numerous. These patches can be seen even when the angle-action coordinates of an erroneous Galactic potential are used, but using the wrong potential displaces them. Diagnostic quantities constructed from the angle coordinates both allow the true potential to be identified, and the relic to be dated. Hence when the full phase space coordinates of large numbers of solar-neighbourhood stars are known, it should be possible to identify members of particular relics from the distribution of stars in an approximate action space. This would then open up the possibility of determining the time since the relic was disrupted and gaining better knowledge of the Galactic potential. The availability of angle-action coordinates for arbitrary potentials is the key to these developments. The paper includes a brief introduction to the torus technique used to generate them.