Detection of Chemo-Kinematical Structures in Leo I
  A variety of formation models for dwarf spheroidal (dSph) galaxies have been
proposed in the literature, but these generally have not been quantitatively
compared with observations. We make use of a new spectroscopic data-set for the
Milky Way dSph Leo I, combining 288 stars observed with Magellan/IMACS and
existing Keck/DEIMOS data to provide velocity and metallicity measurements for
953 Leo I member stars. We search for chemo-dynamical patterns in this
data-set, mock galaxies consisting of pure random motions, and simulated dwarfs
formed via the dissolving star cluster and tidal stirring models. In the Leo I
data, we report the detection of 14 candidate streams of stars that may have
originated in disrupted star clusters. The angular momentum vectors of these
streams are randomly oriented, consistent with the lack of rotation in Leo I.
These results are consistent with the predictions of the dissolving cluster
model. In contrast, we find fewer candidate stream signals in mock data-sets
that lack coherent motions ~99% of the time. The chemo-dynamical analysis of
the tidal stirring simulation produces streams that share a common orientation,
which is inconsistent with the Leo~I data.
