A Dynamical Mass Estimate from the Magellanic Stream
  We present a model for the formation of the Magellanic Stream (MS) due to ram
pressure stripping. We model the history of the Small and Large Magellanic
Clouds in the recent cosmological past in a static Milky Way potential with
diffuse halo gas, using observationally motivated orbits for the Magellanic
Clouds derived from HST proper motions within the potential of the Milky Way.
This model is able to reproduce the trailing arm but does not reproduce the
leading arm feature, which is common for models of the stream formation that
include ram pressure stripping effects. Our model produces a good match to
observations (including the densities and line-of-sight velocities of the
stream, as well as the positions and velocities of the satellites at present
day) when we include a diffuse halo component for the Milky Way. From analyzing
our grid of models, we find that there is a direct correlation between the
observed stream length in our simulations and the mass of the Milky Way. For
the observed MS length, the inferred Milky Way mass is $1.5 \pm 0.3 \times
10^{12}$ $M_\odot$, which agrees closely with other independent measures of the
Milky Way mass. We also discuss the MS in the context of HI streams in galaxy
clusters, and find that the MS lies on the low-mass end of a continuum from
Hickson groups to the Virgo cluster. As a tracer of the dynamical mass in the
outer halo, the MS is a particularly valuable probe of the Milky Way's
potential.
