The role of magnetic fields in the structure and interaction of
  supershells
  Large-scale shocks formed by clustered feedback of young OB stars are
considered an important source of mechanical energy for the ISM and a trigger
of molecular cloud formation. Their interaction sites are locations where
kinetic energy and magnetic fields are redistributed between ISM phases. In
this work we study the effect of the magnetic field on the expansion and
fragmentation of supershells and look for the signatures of supershell
collisions on dense structures and on the kinetic and magnetic energy
distribution of the ISM. We performed a series of high-resolution,
three-dimensional simulations of colliding supershells. The shocks are created
by time-dependent feedback and evolve in a diffuse turbulent environment that
is either unmagnetized or has different initial magnetic field configurations.
In the hydrodynamical situation, the expansion law of the superbubbles is
consistent with the radius-time relation that is theoretically predicted for
wind-blown bubbles. The supershells fragment over their entire surface into
small dense clumps that carry more than half of the total kinetic energy in the
volume. However, this is not the case when a magnetic field is introduced,
either in the direction of the collision or perpendicular to the collision. In
magnetized situations, the shell surfaces are more stable to dynamical
instabilities. When the magnetic field opposes the collision, the expansion law
of the supershells also becomes significantly flatter than in the
hydrodynamical case. Although a two-phase medium arises in all cases, in the
MHD simulations the cold phase is limited to lower densities.
