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

Abstract

We present the molecular gas mass fraction (f H2 ) 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 H2 and SFE have strong positive correlations with the SFR offset from the star-forming main sequence (∆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 ∆MS distribution of the sample when investigating the environmental effects on the H 2 gas content in galaxies.

Similar Scaling Relations for the Gas Content of Galaxies Across Environments to z ∼ 3.5

“…We also found no evidence for a different depletion timescale in denser environments than the field to z ∼ 3.5 consistent with e.g. Koyama et al (2017) at z ∼ 0 and Noble et al (2017) at z ∼ 1.6. However, some studies have suggested that denser environments accelerate (decelerate) the consumption of molecular gas, leading to a shorter (longer) τ in denser regions (e.g.…”

“…This is supported by the lack of environmental effects on the molecular gas content of galaxies as seen in some studies (e.g. ; Kenney & Young 1989;Koyama et al 2017). However, others find lower (e.g.…”

“…These automatically bias the denser environment samples to higher M * and lower sSFR/sSFR MS distributions, both leading to lower gas content for galaxies in denser environments. The role of selection biases is recently highlighted by Koyama et al (2017) who found no environmental effects on molecular gas and star-formation efficiency at z ∼ 0 after controlling for potential biases.…”

Do Galaxy Morphologies Really Affect the Efficiency of Star Formation During the Phase of Galaxy Transition?

“…We performed data reduction by following the procedure described in Koyama et al (2017) using the NEW-STAR software developed by NRO based on the Astronomical Image Processing System (AIPS) package. We only used the data with wind velocities of < 5 m s −1 , pointing accuracies with <5 , system noise temperature (T sys ) with <300 K, and the data with the rms noise temperature of T rms < 0.045 K in the T mb scale at a velocity resolution of 200 km s −1 to exclude bad baseline spectra.…”

Molecular Gas Reservoirs in Cluster Galaxies at z = 1.46

“…Gas fraction and star formation efficiency of galaxies can be responsible for deviation from the main sequence in the plane of SFR-M stellar , in the sense that starburst (passive) galaxies tend to have larger (smaller) gas fraction and/or higher (lower) efficiency of star formation (Saintonge et al 2012(Saintonge et al , 2016(Saintonge et al , 2017Sargent et al 2014). On the other hand, as long as we focus on star-forming galaxies, an environment where galaxies reside do not have a strong impact on the star-forming main sequence and the relationship between gas reservoirs and star-formation activity (Peng et al 2010;Koyama et al 2017). These observational studies may suggest that star formation activity in most of galaxies is governed not by external process such as galaxy interaction but by internal factors such as gas reservoir.…”