HI Power Spectra and the Turbulent ISM of Dwarf Irregular Galaxies
  HI spatial power spectra (PS) were determined for a sample of 24 nearby dwarf
irregular galaxies selected from the LITTLE THINGS (Local Irregulars That Trace
Luminosity Extremes - The HI Nearby Galaxy Survey) sample. The two-dimensional
(2D) power spectral indices asymptotically become a constant for each galaxy
when a significant part of the line profile is integrated. For narrow channel
maps, the PS become shallower as the channel width decreases, and this
shallowing trend continues to our single channel maps. This implies that even
the highest velocity resolution of 1.8 km/s is not smaller than the thermal
dispersion of the coolest, widespread HI component. The one-dimensional PS of
azimuthal profiles at different radii suggest that the shallower PS for
narrower channel width is mainly contributed by the inner disks, which
indicates that the inner disks have proportionally more cooler HI than the
outer disks. Galaxies with lower luminosity (M_B > -14.5 mag) and star
formation rate (SFR, log(SFR (M\odot/yr)) < -2.1) tend to have steeper PS,
which implies that the HI line-of-sight depths can be comparable with the
radial length scales in low mass galaxies. A lack of a correlation between the
inertial-range spectral indices and SFR surface density implies that either
non-stellar power sources are playing a fundamental role in driving the
interstellar medium (ISM) turbulent structure, or the nonlinear development of
turbulent structures has little to do with the driving sources.
