The role of the halo magnetic field on accretion through High-Velocity
  Clouds
  High-Velocity Clouds (HVCs) are believed to be an important source of gas
accretion for star formation in the Milky Way. Earlier numerical studies have
found that the Galactic magnetic field and radiative cooling strongly affects
accretion. However, these effects have not previously been included together in
the context of clouds falling through the Milky Way's gravitational potential.
We explore this by simulating an initially stationary cloud falling through the
hot hydrostatic corona towards the disc. This represents a HVC that has
condensed out of the corona. We include the magnetic field in the corona to
examine its effect on accretion of the HVC and its associated cold gas.
Remnants of the original cloud survive in all cases, although a strong magnetic
field causes it to split into several fragments. We find that mixing of cold
and hot gas leads to cooling of coronal gas and an overall growth with time in
cold gas mass, despite the low metallicity of the cloud and corona. The role of
the magnetic field is to (moderately to severely) suppress the mixing and
subsequent cooling, which in turn leads to less accretion compared to when the
field is absent. A stronger field leads to less suppression of condensation
because it enhances Rayleigh-Taylor instability. However, magnetic tension in a
stronger field substantially decelerates condensed cloudlets. These have
velocities typically a factor 3-8 below the velocity of the main cloud remnants
by the end of the simulation. Some of these cloudlets likely disperse before
reaching the disc.
