Ionized Gas in the Galactic Center: New Observations and Interpretation
  We present new observations of the [Ne II] emission from the ionized gas in
Sgr A West with improved resolution and sensitivity. About half of the emission
comes from gas with kinematics indicating it is orbiting in a plane tipped
about 25\degree\ from the Galactic plane. This plane is consistent with that
derived previously for the circumnuclear molecular disk and the northern arm
and western arc ionized features. However, unlike most previous studies, we
conclude that the ionized gas is not moving along the ionized features, but on
more nearly circular paths. The observed speeds are close to, but probably
somewhat less than expected for orbital motions in the potential of the central
black hole and stars and have a small inward component. The spatial
distribution of the emission is well fitted by a spiral pattern. We discuss
possible physical explanations for the spatial distribution and kinematics of
the ionized gas, and conclude that both may be best explained by a one-armed
spiral density wave, which also accounts for both the observed low velocities
and the inward velocity component. We suggest that a density wave may result
from the precession of elliptical orbits in the potential of the black hole and
stellar mass distribution.
