The Proper Motion Field Along the Magellanic Bridge: a New Probe of the
  LMC-SMC Interaction
  We present the first detailed kinematic analysis of the proper motions (PMs)
of stars in the Magellanic Bridge, from both the \textit{Gaia} Data Release 2
catalog and from \textit{Hubble Space Telescope} Advanced Camera for Surveys
data. For the \textit{Gaia} data, we identify and select two populations of
stars in the Bridge region, young main sequence (MS) and red giant stars. The
spatial locations of the stars are compared against the known H {\small I} gas
structure, finding a correlation between the MS stars and the H {\small I} gas.
In the \textit{Hubble Space Telescope} fields our signal comes mainly from an
older MS and turn-off population, and the proper motion baselines range between
$\sim 4$ and 13 years. The PMs of these different populations are found to be
consistent with each other, as well as across the two telescopes. When the
absolute motion of the Small Magellanic Cloud is subtracted out, the residual
Bridge motions display a general pattern of pointing away from the Small
Magellanic Cloud towards the Large Magellanic Cloud. We compare in detail the
kinematics of the stellar samples against numerical simulations of the
interactions between the Small and Large Magellanic Clouds, and find general
agreement between the kinematics of the observed populations and a simulation
in which the Clouds have undergone a recent direct collision.
