Galactic potential constraints from clustering in action space of
  combined stellar stream data
  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 $M(< 20\ \mathrm{kpc}) = 3.12^{+3.21}_{-0.46} \times
10^{11} \ M_{\odot}$.
