Revisiting the Origin of the Star-Forming Main Sequence Based on a Volume-Limited Sample of ~25,000 Galaxies

TL;DR

This study uses a large, volume-limited galaxy sample to analyze the fundamental drivers of star formation, revealing that the star-forming main sequence results from the interplay of molecular gas and stellar mass relations.

Contribution

It provides a comprehensive statistical analysis linking the star-forming main sequence to molecular gas and stellar mass relations, clarifying their fundamental roles.

Findings

Global relations between SFR, stellar mass, and molecular gas surface densities are established.

Scatter in KS and MGMS relations is smaller than in the SFR-stellar mass relation.

The correlation between SFR surface density and stellar mass surface density is mediated by molecular gas surface density.

Abstract

We revisit the extensively debated star-forming main sequence (SFMS)-a tight correlation between the star formation rate and stellar mass in both kiloparsec-resolved and integrated galaxies. We statistically explore the fundamental drivers of star formation at global scales, using a large volume-limited sample of 24,954 local star-forming galaxies to overcome the limitations of previous works. Based on the mid-infrared 12 micron luminosity, stellar mass, and g-r color, we estimate the molecular gas mass for the considered sample. At galaxy-wide scales, we establish global relations between the surface densities of the star formation rate, stellar mass, and molecular gas mass . These global density relations are connected with and follow similar trends as the resolved SFMS, the Kennicutt-Schmidt (KS) relation, and the molecular gas main sequence (MGMS). Taking advantage of this large catalog, we show that the scatters in the global KS and MGMS relations are smaller than that of the global relation between the star formation rate surface density and stellar mass surface density, and their Pearson correlation coefficients are higher. More importantly, multivariate regression and partial correlation analyses demonstrate that the apparent correlation between the star formation rate surface density and stellar mass surface density is entirely mediated by the molecular gas surface density, with its best-fit parameters directly derivable from those of the KS and MGMS relations. Overall, our findings suggest that the correlation between stellar mass and molecular gas, as well as that between molecular gas and star formation, are more direct and fundamental. The star-forming main sequence thus appears to be a natural by-product of these two tighter relations.