The orientations of molecular clouds in the outer Galaxy: Evidence for
  the scale of the turbulence driver ?
  Supernova explosions inject a considerable amount of energy into the
interstellar medium (ISM) in regions with high to moderate star formation
rates. In order to assess whether the driving of turbulence by supernovae is
also important in the outer Galactic disk, where the star formation rates are
lower, we study the spatial distribution of molecular cloud (MC) inclinations
with respect to the Galactic plane. The latter contains important information
on the nature of the mechanism of energy injection into the ISM. We analyze the
spatial correlations between the position angles (PAs) of a selected sample of
MCs (the largest clouds in the catalogue of the outer Galaxy published by Heyer
et al. 2001). Our results show that when the PAs of the clouds are all mapped
to values into the [0,90]degrees interval, there is a significant degree of
spatial correlation between the $PA$s on spatial scales in the range of 100-800
pc. These scales are of the order of the sizes of individual SN shells in low
density environments such as those prevailing in the outer Galaxy and where the
metallicity of the ambient gas is of the order of the solar value or smaller.
These findings suggest that individual SN explosions, occurring in the outer
regions of the Galaxy and in likewise spiral galaxies, albeit at lower rates,
continue to play an important role in shaping the structure and dynamics of the
ISM in those regions. The SN explosions we postulate here are likely associated
with the existence of young stellar clusters in the far outer regions of the
Galaxy and the UV emission and low levels of star formation observed with the
GALEX satellite in the outer regions of local galaxies.
