A universal correlation between star-formation activity and molecular gas properties across environments

TL;DR

This study reveals a universal correlation between star-formation activity and molecular gas properties in local galaxies, independent of their environment, emphasizing the primary role of molecular gas in star formation.

Contribution

It provides the first systematic analysis showing that molecular gas fraction and star-formation efficiency correlate universally with star formation activity across diverse environments.

Findings

Both $f_\mathrm{H_2}$ and SFE strongly correlate with $\Delta$MS.

These correlations are consistent across all environments.

Star-formation activity is mainly governed by molecular gas content.

Abstract

We present the molecular gas mass fraction ($f_\mathrm{H_2}$) and star-formation efficiency (SFE) of local galaxies on the basis of our new CO($J=1-0$) observations with the Nobeyama 45m radio telescope, combined with the COLDGASS galaxy catalog, as a function of galaxy environment defined as the local number density of galaxies measured with SDSS DR7 spectroscopic data. Our sample covers a wide range in the stellar mass and SFR, and covers wide environmental range over two orders of magnitude. This allows us to conduct the first, systematic study of environmental dependence of molecular gas properties in galaxies from the lowest- to the highest-density environments in the local universe. We confirm that both $f_\mathrm{H_2}$ and SFE have strong positive correlations with the SFR offset from the star-forming main sequence ($\Delta$MS), and most importantly, we find that these correlations are universal across all environments. Our result demonstrates that star-formation activity within individual galaxies is primarily controlled by their molecular gas content, regardless of their global environment. Therefore, we claim that one always needs to be careful about the $\Delta$MS distribution of the sample when investigating the environmental effects on the H$_2$ gas content in galaxies.