What's Up in the Milky Way? The Orientation of the Disc Relative to the
  Triaxial Halo
  Models of the Sagittarius Stream have consistently found that the Milky Way
disc is oriented such that its short axis is along the intermediate axis of the
triaxial dark matter halo. We attempt to build models of disc galaxies in such
an `intermediate-axis orientation'. We do this with three models. In the first
two cases we simply rigidly grow a disc in a triaxial halo such that the disc
ends up perpendicular to the global intermediate axis. We also attempt to coax
a disc to form in an intermediate-axis orientation by producing a gas+dark
matter triaxial system with gas angular momentum about the intermediate axis.
In all cases we fail to produce systems which remain with stellar angular
momentum aligned with the halo's intermediate axis, even when the disc's
potential flattens the inner halo such that the disc is everywhere
perpendicular to the halo's local minor axis. For one of these unstable
simulations we show that the potential is even rounder than the models of the
Milky Way potential in the region probed by the Sagittarius Stream. We conclude
that the Milky Way's disc is very unlikely to be in an intermediate axis
orientation. However we find that a disc can persist off one of the principal
planes of the potential. We propose that the disc of the Milky Way must be
tilted relative to the principal axes of the dark matter halo. Direct
confirmation of this prediction would constitute a critical test of Modified
Newtonian Dynamics.
