Ph.D defense: H I Kinematics and Star Formation Rate in LITTLE THINGS Galaxies
by Nau Raj Pokhrel, adviser Dr. C. Simpson
We present a catalog and analysis of the properties of neutral hydrogen gas (H I) holes/shells in the LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey) galaxies. LITTLE THINGS uses high angular resolution (6''), high spectral resolution (≤ 2.6 km s–1), and high sensitivity (≤ 1.1 mJy beam–1 channel–1) H I observations of 41 nearby (≤ 10.3 Mpc) gas-rich dwarf galaxies. Dwarf galaxies are the most common type of galaxy in the local universe and they are believed to be the first galaxies to form. Here we study the interaction between star formation and the interstellar medium from which stars form. In the sample of galaxies, we detected 306 H I holes with sizes ranging from about 38 pc to 2.3 kpc, expansion rates varying from 5 to 30 km s–1, and estimated kinetic ages varying from 1 Myr to 127 Myr. The distribution of holes per unit area is found nearly constant both inside (51%) and outside (49%) of the V-band break radius, where the radial luminosity function changes slope. We derived surface and volume porosity and found that porosity doesn't correlate with star formation rate (SFR) for the LITTLE THINGS sample. Assuming that the holes are formed from the stellar feedback, we calculated the supernova rate (SNR) and the SFR. We did find a correlation between the SFR calculated from Hα (a star formation tracer) and the SFR estimated from the SNR, consistent with hole formation from stellar feedback.