A Dwarf Disrupting -- Andromeda XXVII and the North West Stream
  We present a kinematic and spectroscopic analysis of 38 red giant branch
stars, in 7 fields, spanning the dwarf spheroidal galaxy Andromeda XXVII and
the upper segment of the North West Stream. Both features are located in the
outer halo of the Andromeda galaxy at a projected radius of 50-80 kpc, with the
stream extending for $\sim$3$^{\circ}$ on the sky. Our data is obtained as part
of the PAndAS survey and enables us to confirm that Andromeda XXVII's
heliocentric distance is 827 $\pm$ 47 kpc and spectroscopic metallicity is
-2.1$^{+0.4}_{-0.5}$. We also re-derive Andromeda XXVII's kinematic properties,
measuring a systemic velocity = -526.1$^{+10.0}_{-11.0}${\kms} and a velocity
dispersion that we find to be non-Gaussian but for which we derive a formal
value of 27.0$^{+2.2}_{-3.9}${\kms}. In the upper segment of the North West
Stream we measure mean values for the metallicity = -1.8$\pm$0.4, systemic
velocity = -519.4 $\pm$4.0{\kms} and velocity dispersion = 10.0$\pm$4.0{\kms}.
We also detect a velocity gradient of 1.7$\pm$0.3 {\kms} kpc$^{-1}$ on an
infall trajectory towards M31. With a similar gradient, acting in the same
direction, in the lower segment we suggest that the North West Stream is not a
single structure. As the properties of the upper segment of the North West
Stream and Andromeda XXVII are consistent within ~90\% confidence limits, it is
likely that the two are related and plausible that Andromeda XXVII is the
progenitor of this stream.
