NGC5466: A unique probe of the galactic halo shape

Abstract

Stellar streams provide unique probes of galactic potentials, with the longer streams normally providing the cleaner measurements. In this Letter, 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 NGC5466. 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 MilkyWay disc properties and the specific halo parametrization chosen); spherical or prolate halo shapes can be excluded at a high confidence level. Therefore, more extensive data sets along the NGC5466 tidal stream promise strong constraints on the Milky Way halo shape. © 2012 The Authors, MNRAS 424, L16-L20 Monthly Notices of the Royal Astronomical Society © 2012 RAS.