Red Giants in the Small Magellanic Cloud. I. Disk and Tidal Stream
  Kinematics
  We present results from an extensive spectroscopic survey of field stars in
the Small Magellanic Cloud (SMC). 3037 sources, predominantly first-ascent red
giants, spread across roughly 37.5 sq. deg, are analysed. The line of sight
velocity field is dominated by the projection of the orbital motion of the SMC
around the LMC/Milky Way. The residuals are inconsistent with both a
non-rotating spheroid and a nearly face on disk system. The current sample and
previous stellar and HI kinematics can be reconciled by rotating disk models
with line of nodes position angle, theta, ~ 120-130 deg., moderate inclination
(i ~ 25-70 deg.), and rotation curves rising at 20-40 km/s/kpc. The metal-poor
stars exhibit a lower velocity gradient and higher velocity dispersion than the
metal-rich stars. If our interpretation of the velocity patterns as bulk
rotation is appropriate, then some revision to simulations of the SMC orbit is
required since these are generally tuned to the SMC disk line-of-nodes lying in
a NE-SW direction. Residuals show strong spatial structure indicative of
non-circular motions that increase in importance with increasing distance from
the SMC centre. Kinematic substructure in the north-west part of our survey
area is associated with the tidal tail or Counter-Bridge predicted by
simulations. Lower line-of-sight velocities towards the Wing and the larger
velocities just beyond the SW end of the SMC Bar are probably associated with
stellar components of the Magellanic Bridge and Counter-Bridge, respectively.
Our results reinforce the notion that the intermediate-age stellar population
of the SMC is subject to substantial stripping by external forces.
