Reorienting MHD Colliding Flows: A Shock Physics Mechanism for
  Generating Filaments Normal to Magnetic Fields
  We present numerical simulations of reorienting oblique shocks that form in
the collision layer between magnetized colliding flows. Reorientation aligns
parsec-scale post-shock filaments normal to the background magnetic field. We
find that reorientation begins with pressure gradients between the collision
region and the ambient medium. This drives a lateral expansion of post-shock
gas, which reorients the growing filament from the outside-in (i.e. from the
flow-ambient boundary, toward the colliding flows axis). The final structures
of our simulations resemble polarization observations of filaments in Taurus
and Serpens South, as well as the integral-shaped filament in Orion A. Given
the ubiquity of colliding flows in the interstellar medium, shock reorientation
may be relevant to the formation of filaments normal to magnetic fields.
