Collisions between Dark Matter Confined High Velocity Clouds and
  Magnetized Galactic Disks: The Smith Cloud
  The Galaxy's population of High Velocity Clouds (HVCs) may include a
subpopulation that is confined by dark matter minihalos and falling toward the
Galactic disk. We present the first magnetohydrodynamic simulational study of
dark matter-dominated HVCs colliding with a weakly magnetized galactic disk.
Our HVCs have baryonic masses of $5 \times 10^6\,$M$_{\odot}$ and dark matter
minihalo masses of 0, $3 \times 10^8$, or $1 \times 10^9\,$M$_{\odot}$. They
are modeled on the Smith Cloud, which is said to have collided with the disk 70
Myr ago. We find that, in all cases, the cloud's collision with the galactic
disk creates a hole in the disk, completely disperses the cloud, and forms a
bubble-shaped structure on the far side of the disk. In contrast, when present,
the dark matter minihalo continues unimpeded along its trajectory. Later, as
the minihalo passes through the bubble structure and galactic halo, it accretes
up to $6.0 \times 10^5\,$M$_{\odot}$ in baryonic material, depending on the
strengths of the magnetic field and minihalo gravity. These simulations suggest
that if the Smith Cloud is associated with a dark matter minihalo and collided
with the Galactic disk, the minihalo has accreted the observed gas. However, if
the Smith Cloud is dark matter-free, it is on its first approach toward the
disk. These simulations also suggest that the dark matter is most concentrated
either at the head of the cloud or near the cloud, depending upon the strength
of the magnetic field, a point that could inform indirect dark matter searches.
