HIghMass - High HI Mass, HI-Rich Galaxies at $z\sim0$: Combined HI and H$_2$ Observations

TL;DR

This study investigates three high HI mass, gas-rich galaxies at z~0, revealing that their star formation bottleneck lies in converting HI to H2, with implications for galaxy evolution and star formation efficiency.

Contribution

The paper provides detailed resolved HI and CO observations of HIghMass galaxies, highlighting the role of HI to H2 conversion in star formation regulation.

Findings

Star formation efficiency is limited by HI to H2 conversion.

Galaxies have normal star formation rates for their HI mass.

Dark matter spin parameters are above average, influencing star formation history.

Abstract

We present resolved HI and CO observations of three galaxies from the HIghMass sample, a sample of HI-massive ($M_{HI} > 10^{10} M_\odot$), gas-rich ($M_{HI}$ in top $5\%$ for their $M_*$) galaxies identified in the ALFALFA survey. Despite their high gas fractions, these are not low surface brightness galaxies, and have typical specific star formation rates (SFR$/M_*$) for their stellar masses. The three galaxies have normal star formation rates for their HI masses, but unusually short star formation efficiency scale lengths, indicating that the star formation bottleneck in these galaxies is in the conversion of HI to H$_2$, not in converting H$_2$ to stars. In addition, their dark matter spin parameters ($\lambda$) are above average, but not exceptionally high, suggesting that their star formation has been suppressed over cosmic time but are now becoming active, in agreement with prior H$\alpha$ observations.