The HI∕Star Formation Connection

Abstract

There have been many observational programs exploring the connection between the HI distribution and the presence of star formation in galaxies. Since the molecular phase of the ISM is most closely associated with star formation, the results of these investigations depend greatly on the type of galaxy being observed. For low mass, low metallicity galaxies, where the molecular gas in only found associated with the densest concentrations of HI, the correlation between HI maxima and star formation is very good. For high mass, high metallicity galaxies, star formation correlates strongly with densest concentrations of molecular gas, and the majority of the HI gas can be unrelated to star formation. Understanding the HI/star formation connection requires observations of the quality being produced by the THINGS program. The THINGS sample is especially promising due to the abundance and quality of the ancillary observational databases. As a forward look, I pose the question: How many galaxies do we need to observe with this quality of data in order to answer our fundamental questions concerning the star formation process? An important part of the answer is that we need to carefully study those galaxies and regions of galaxies which do not show current star formation in order to understand the absence of star formation as well as the presence of star formation. I describe a method of recreating star formation histories of galaxies over the last ∼500 Myr which will help us to understand how the gas has come to its present state.