The SPLASH Survey: A Spectroscopic Portrait of Andromeda's Giant
  Southern Stream
  The giant southern stream (GSS) is the most prominent tidal debris feature in
M31's stellar halo. The GSS is composed of a relatively metal-rich, high
surface-brightness "core" and a lower metallicity, lower surface brightness
"envelope." We present Keck/DEIMOS spectroscopy of red giant stars in six
fields in the vicinity of M31's GSS and one field on Stream C, an arc-like
feature on M31's SE minor axis at R=60 kpc. Several GSS-related findings and
measurements are presented here. We present the innermost kinematical detection
of the GSS core to date (R=17 kpc). This field also contains the continuation
of a second kinematically cold component originally seen in a GSS core field at
R=21 kpc. The velocity gradients of the GSS and the second component in the
combined data set are parallel over a radial range of 7 kpc, suggesting a
possible bifurcation in the line-of-sight velocities of GSS stars. We also
present the first kinematical detection of substructure in the GSS envelope.
Using kinematically identified samples, we show that the envelope debris has a
~0.7 dex lower mean photometric metallicity and possibly higher intrinsic
velocity dispersion than the GSS core. The GSS is also identified in the field
of the M31 dSph satellite And I; the GSS in this field has a metallicity
distribution identical to that of the GSS core. We confirm the presence of two
kinematically cold components in Stream C, and measure intrinsic velocity
dispersions of ~10 and ~4 km/s. This compilation of the kinematical (mean
velocity, intrinsic velocity dispersion) and chemical properties of stars in
the GSS core and envelope, coupled with published surface brightness
measurements and wide-area star-count maps, will improve constraints on the
orbit and internal structure of the dwarf satellite progenitor.
