Dark impact and galactic star formation: Origin of the Gould belt
  The Milky Way has a giant stellar structure in the solar neighborhood, which
has a size of $\sim 1$ kpc, a mass of $\sim 10^6 {\rm M}_{\odot}$, and a
ring-like distribution of young stars. Fundamental physical properties of this
local enigmatic structure, known as the Gould belt (GB), have not been
reproduced by previously proposed models. We first show that the local
enigmatic structure can be formed about 30 Myr ago as a result of a high-speed,
oblique collision between a gas cloud with a mass of $\sim 10^6 {\rm
M}_{\odot}$ and a dark matter clump with a mass of $\sim 10^7 {\rm M}_{\odot}$
based on numerical simulations of the collision. We find that strong dynamical
impact of the clump transforms the flattened cloud into a ring-like stellar
structure after induced star formation within the cloud. Our simulations
furthermore demonstrate that the stellar structure is moderately elongated and
significantly inclined with respect to the disk of the Milky Way owing to the
strong tidal torque by the colliding clump. We thus suggest that the GB is one
of stellar substructures formed from collisions between gas clouds and dark
matter clumps predicted in the hierarchical clustering scenario of galaxy
formation. We also suggest that collisions of dark matter clumps with their
host galaxies can significantly change star formation histories for some of
their gas clouds thus influence galactic global star formation histories to
some extent.
