3D simulations of globules and pillars formation around HII regions:
  turbulence and shock curvature
  We investigate the interplay between the ionization radiation from massive
stars and the turbulence inside the surrounding molecular gas thanks to 3D
numerical simulations. We used the 3D hydrodynamical code HERACLES to model an
initial turbulent medium that is ionized and heated by an ionizing source.
Three different simulations are performed with different mean Mach numbers (1,
2 and 4). A non-equilibrium model for the ionization and the associated thermal
processes was used. This revealed to be crucial when turbulent ram pressure is
of the same order as the ionized-gas pressure. The density structures initiated
by the turbulence cause local curvatures of the dense shell formed by the
ionization compression. When the curvature of the shell is sufficient, the
shell collapse on itself to form a pillar while a smaller curvature leads to
the formation of dense clumps that are accelerated with the shell and therefore
remain in the shell during the simulation. When the turbulent ram pressure of
the cold gas is sufficient to balance the ionized-gas pressure, some dense-gas
bubbles have enough kinetic energy to penetrate inside the ionized medium,
forming cometary globules. This suggests a direct relation in the observations
between the presence of globules and the relative importance of the turbulence
compared to the ionized-gas pressure. The probability density functions present
a double peak structure when the turbulence is low relative to the ionized-gas
pressure. This could be used in observations as an indication of the turbulence
inside molecular clouds.
