Centrally Concentrated H I Distribution Enhances Star Formation in Galaxies

TL;DR

This study finds that galaxies with centrally concentrated H I gas, indicated by a new shape parameter, tend to have higher star formation rates, highlighting the importance of H I distribution in star formation processes.

Contribution

Introduces a new non-parametric measure of H I profile shape ($K$) to link gas distribution with star formation activity in galaxies.

Findings

Higher $K$ values correlate with more centrally concentrated H I.

Galaxies with higher $K$ have increased total and central SFR.

Centrally concentrated H I facilitates molecular gas formation and star formation.

Abstract

We use a sample of 13,511 nearby galaxies from the ALFALFA and SDSS spectroscopic surveys to study the relation between the spatial distribution of H I 21 cm emission and star formation rate (SFR). We introduce a new non-parametric quantity $K$, measured from the curve-of-growth of the line, to describe the shape of the integrated H I profile. The value of $K$ increases from double-horned to single-peaked profiles, depending on projection effects and the spatial and velocity distribution of the gas. Using carefully chosen samples to control for the competing factors that influence the integrated line profile, we argue that useful inferences can be made on the spatial distribution of the gas. We find that galaxies with a high value of $K$ tend to have more centrally concentrated H I distribution within the optical disk of the galaxy at fixed conditions, and that larger values of $K$ are associated with higher levels of total and central SFR. The results suggest that the global concentration of H I plays an important role in facilitating the conversion of neutral atomic hydrogen to molecular hydrogen gas, which, in turn, affects the star formation activity throughout the optical disk. Our sample is biased against quiescent galaxies, and thus the conclusions may not hold for galaxies with low SFR or low H I content.