# The Nature of Turbulence in the LITTLE THINGS Dwarf Irregular Galaxies

## TL;DR

This study analyzes the turbulence in dwarf irregular galaxies by examining HI density distributions, revealing correlations between turbulence metrics and star formation, and modeling the effects of Mach number and molecular conversion.

## Contribution

It extends previous turbulence analysis methods to a new galaxy sample, linking HI density distribution statistics to physical conditions and star formation activity.

## Key findings

- Kurtosis correlates with skewness in HI distributions.
- Kurtosis increases with galaxy radius and star formation rate.
- HI column densities decrease with radius, indicating molecular formation at cloud edges.

## 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.