Misc,
The Nature of Turbulence in the LITTLE THINGS Dwarf Irregular Galaxies
(2017)cite arxiv:1703.00529Comment: AJ, in press.
Abstract
We present probability density functions and higher order (skewness and
kurtosis) analyses of the galaxy-wide and spatially-resolved HI column density
distributions in the LITTLE THINGS sample of dwarf irregular galaxies. This
analysis follows that of Burkhart et al. (2010) for the Small Magellanic Cloud.
About 60% of our sample have galaxy-wide values of kurtosis that are similar to
that found for the Small Magellanic Cloud, with a range up to much higher
values, and kurtosis increases with integrated star formation rate. Kurtosis
and skewness were calculated for radial annuli and for a grid of 32 pixel X 32
pixel kernels across each galaxy. For most galaxies, kurtosis correlates with
skewness. For about half of the galaxies, there is a trend of increasing
kurtosis with radius. The range of kurtosis and skewness values is modeled by
small variations in the Mach number close to the sonic limit and by conversion
of HI to molecules at high column density. The maximum HI column densities
decrease with increasing radius in a way that suggests molecules are forming in
the weak field limit, where H_2 formation balances photodissociation in
optically thin gas at the edges of clouds.
