Galactic potential constraints from clustering in action space of combined stellar stream data

TL;DR

This paper develops a method to constrain the Milky Way's gravitational potential by fitting multiple stellar streams simultaneously in action space, improving mass estimates within 20 kpc.

Contribution

It introduces a technique to combine multiple stellar streams in action space for more accurate Galactic potential constraints, accounting for biases in individual streams.

Findings

Combined streams constrain mass within 20 kpc to approximately 3 x 10^11 solar masses.

Including the Helmi stream increases the mass uncertainty significantly.

The strongest constraints come from GD-1, Pal 5, and Orphan streams.

Abstract

Stream stars removed by tides from their progenitor satellite galaxy or globular cluster act as a group of test particles on neighboring orbits, probing the gravitational field of the Milky Way. While constraints from individual streams have been shown to be susceptible to biases, combining several streams from orbits with various distances reduces these biases. We fit a common gravitational potential to multiple stellar streams simultaneously by maximizing the clustering of the stream stars in action space. We apply this technique to members of the GD-1, Pal 5, Orphan and Helmi streams, exploiting both the individual and combined data sets. We describe the Galactic potential with a St\"ackel model, and vary up to five parameters simultaneously. We find that we can only constrain the enclosed mass, and that the strongest constraints come from the GD-1, Pal 5 and Orphan streams whose combined data set yields $M(< 20\ \mathrm{kpc}) = 2.96^{+0.25}_{-0.26} \times 10^{11} \ M_{\odot}$. When including the Helmi stream in the data set, the mass uncertainty increases to $M(< 20\ \mathrm{kpc}) = 3.12^{+3.21}_{-0.46} \times 10^{11} \ M_{\odot}$.