Stochastic Noncircular Motion and Outflows Driven by Magnetic Activity
  in the Galactic Bulge Region
  By performing a global magneto-hydrodynamical simulation for the Milky Way
with an axisymmetric gravitational potential, we propose that spatially
dependent amplification of magnetic fields possibly explains the observed
noncircular motion of the gas in the Galactic center region. The radial
distribution of the rotation frequency in the bulge region is not monotonic in
general. The amplification of the magnetic field is enhanced in regions with
stronger differential rotation, because magnetorotational instability and
field-line stretching are more effective. The strength of the amplified
magnetic field reaches >~ 0.5 mG, and radial flows of the gas are excited by
the inhomogeneous transport of angular momentum through turbulent magnetic
field that is amplified in a spatially dependent manner. In addition, the
magnetic pressure-gradient force also drives radial flows in a similar manner.
As a result, the simulated position-velocity diagram exhibits a time-dependent
asymmetric parallelogram-shape owing to the intermittency of the magnetic
turbulence; the present model provides a viable alternative to the
bar-potential-driven model for the parallelogram-shape of the central molecular
zone. This is a natural extension into the central few 100 pc of the magnetic
activity, which is observed as molecular loops at radii from a few 100 pc to 1
kpc. Furthermore, the time-averaged net gas flow is directed outward, whereas
the flows are highly time-dependent, which we discuss from a viewpoint of the
outflow from the bulge.
