NGC 5466: a unique probe of the Galactic halo shape

TL;DR

This paper demonstrates that the short NGC 5466 stellar stream is highly sensitive to the Milky Way's dark matter halo shape, favoring oblate or triaxial configurations over spherical or prolate ones.

Contribution

It shows that even short stellar streams can effectively constrain the shape of the galactic halo, providing a new method for probing dark matter distribution.

Findings

Deviations in the stream suggest an oblate or triaxial halo.

Spherical or prolate halos are statistically excluded.

Short streams can yield strong halo shape constraints.

Abstract

Stellar streams provide unique probes of galactic potentials, with the longer streams normally providing the cleaner measurements. In this paper, we show an example of a short tidal stream that is particularly sensitive to the shape of the Milky Way's dark matter halo: the globular cluster tidal stream NGC 5466. This stream has an interesting deviation from a smooth orbit at its western edge. We show that such a deviation favours an underlying oblate or triaxial halo (irrespective of plausible variations in the Milky Way disc properties and the specific halo parametrisation chosen); spherical or prolate halo shapes can be excluded at a high confidence level. Therefore, more extensive data sets along the NGC 5466 tidal stream promise strong constraints on the Milky Way halo shape.