Turbulence and Star Formation in a Sample of Spiral Galaxies
  We investigate turbulent gas motions in spiral galaxies and their importance
to star formation in far outer disks, where the column density is typically far
below the critical value for spontaneous gravitational collapse. Following the
methods of Burkhart et al. (2010) on the Small Magellanic Cloud, we use the
third and fourth statistical moments, as indicators of structures caused by
turbulence, to examine the neutral hydrogen (HI) column density of a sample of
spiral galaxies selected from The HI Nearby Galaxy Survey (THINGS, Walter et
al. 2008). We apply the statistical moments in three different methods- the
galaxy as a whole, divided into a function of radii and then into grids. We
create individual grid maps of kurtosis for each galaxy. To investigate the
relation between these moments and star formation, we compare these maps with
their far-ultraviolet images taken by the Galaxy Evolution Explorer (GALEX)
satellite. We find that the moments are largely uniform across the galaxies, in
which the variation does not appear to trace any star forming regions. This
may, however, be due to the spatial resolution of our analysis, which could
potentially limit the scale of turbulent motions that we are sensitive to
greater than ~700 pc. From comparison between the moments themselves, we find
that the gas motions in our sampled galaxies are largely supersonic. This
analysis also shows that Burkhart et al. (2010)'s methods may be applied not
just to dwarf galaxies but also to normal spiral galaxies.
