A Universal Correlation between Star Formation Activity and Molecular Gas Properties Across Environments

We present the molecular gas mass fraction ( f_H2) and star formation efficiency (SFE) of local galaxies on the basisof our new CO(J = 1 - 0) observations with the Nobeyama 45 m radio telescope, combined with theCOLDGASS galaxy catalog, as a function of galaxy environment defined as the local number density of galaxiesmeasured with SDSS DR7 spectroscopic data. Our sample covers a wide range in the stellar mass and starformation rate (SFR), and also covers a wide environmental range over two orders of magnitude. This allows us toconduct the first systematic study of environmental dependence of molecular gas properties in galaxies from thelowest- to the highest-density environments in the local universe. We confirm that both f_H2 and SFE have strongpositive correlations with the SFR offset from the star-forming main sequence (δMS) and, most importantly, wefind that these correlations are universal across all environments. Our result demonstrates that star formationactivity within individual galaxies is primarily controlled by their molecular gas content, regardless of their globalenvironment. Therefore, we claim that one always needs to be careful about the δMS distribution of the samplewhen investigating the environmental effects on the H₂ gas content in galaxies.