The Sagittarius Dwarf Galaxy: a Model for Evolution in a Triaxial Milky
  Way Halo
  We present a new N-body model for the tidal disruption of the Sagittarius
(Sgr) dwarf that is capable of simultaneously satisfying the majority of
angular position, distance, and radial velocity constraints imposed by current
wide-field surveys of its dynamically young (< 3 Gyr) tidal debris streams. In
particular, this model resolves the conflicting angular position and radial
velocity constraints on the Sgr leading tidal stream that have been highlighted
in recent years. While the model does not reproduce the apparent bifurcation
observed in the leading debris stream, recent observational data suggest that
this bifurcation may represent a constraint on the internal properties of the
Sgr dwarf rather than the details of its orbit. The key element in the success
of this model is the introduction of a non-axisymmetric component to the
Galactic gravitational potential which can be described in terms of a triaxial
dark matter halo whose minor/major axis ratio (c/a)_Phi = 0.72 and
intermediate/major axis ratio (b/a)_Phi = 0.99 at radii 20 < r < 60 kpc. The
minor/intermediate/major axes of this halo lie along the directions (l, b) =
(7, 0), (0, 90), and (97, 0) respectively, corresponding to a nearly-oblate
ellipsoid whose minor axis is contained within the Galactic disk plane. We
demonstrate that with simple assumptions about the star formation history of
Sgr, tidal stripping models naturally give rise to gradients in the metallicity
distribution function (MDF) along the stellar debris streams similar to those
observed in recent studies. (Abridged).
