H I Structure and Kinematics of the Interstellar Medium in the LITTLE THINGS Galaxies

We present a catalog of the neutral atomic hydrogen structures (H I holes) and the analysis of their properties in nearby (≤ 10.3 Mpc) gas-rich dwarf galaxies of the LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey) group. We used high sensitivity (≤ 1.1 mJy beam-1 channel-1), high velocity resolution (1.3 km s-1 to 2.6 km s-1) and high linear resolution (average ~110 pc; angular resolution ~6”) H I data of 37 dwarf irregulars and four blue compact dwarf galaxies. We cataloged H I holes in the entire sample and studied the of the properties of holes. We also investigated the effect of H I porosity on star formation, and the correlation of the star formation rate (SFR) calculated from H I holes with standard star formation tracers Hα and FUV. We detected 306 H I holes in LITTLE THINGS galaxies. We confirmed 22 kpc-sized holes, the largest and the smallest hole diameters are about 2.3 kpc and 38 pc (resolution limit) respectively. The expansion velocities of the holes range from 5 km s-1 (upper limit) to 30 km s-1, and the rotational velocities range from 6 km s-1 to 77 km s-1. The H I disk radii of the galaxies range from about 0.5 kpc to 6.7 kpc. The kinetic ages of the holes range from about 1 to 127 Myr, and the estimated scale heights are varying from 61 pc to 653 pc. The percentage distribution of the holes outside and inside the V-band break radius is nearly uniform, 49% and 51% respectively. In LITTLE THINGS galaxies, we found no obvious correlation between the surface and volume porosities, and SFR. However, two highest and two lowest porosity galaxies have no star formation at present. The holes are consistent with the SFR estimated from the energy required to create a hole and the star formation rates measured from Hα and FUV, indicating that the holes are consistent with a star formation origin.