CO Multi-line Imaging of Nearby Galaxies (COMING). XI. Azimuthally averaged star formation rate and stellar mass relation with molecular gas amount

TL;DR

This study examines how star formation rate, stellar mass, and molecular gas content relate on kiloparsec scales in nearby galaxies, revealing different behaviors based on galaxy type and internal structures, and suggesting inside-out quenching processes.

Contribution

It provides a detailed analysis of the spatially resolved relations between star formation, stellar mass, and molecular gas in a large galaxy sample, highlighting the roles of galaxy morphology and environment.

Findings

UMS galaxies have higher SFE and similar gas fractions compared to MS galaxies.

LMS galaxies tend to have lower gas fractions and star formation activity.

Inside-out quenching is supported by the observed decrease in sSFR and gas fraction in galaxy centers.

Abstract

This study investigated the relation between the surface density of star formation rate (SFR) ($\Sigma_{\mathrm{SFR}}$), stellar mass ($\Sigma_{M_{\ast}}$), and molecular gas mass ($\Sigma_{M_\mathrm{mol}}$) on nearly 1 kpc scales averaged over concentric tilted rings using the $^{12}$CO $J=1-0$ mapping data of 92 nearby galaxies obtained in the CO Multi-line Imaging of Nearby Galaxies (COMING) project. We categorized these galaxies into three groups based on the deviation of each global SFR from the star-forming main sequence (MS), $\Delta$MS: upper MS (UMS), MS, and lower MS (LMS). UMS galaxies tend to be less massive or barred spiral galaxies, exhibiting molecular gas fraction ($f_{\mathrm{gas}}$) comparable to those of MS galaxies but higher star formation efficiency (SFE). In contrast, the LMS galaxies tend to be massive or active galaxies hosting an active galactic nucleus (AGN). Their $f_{\mathrm{gas}}$ values are lower than those of MS galaxies, and their SFEs are slightly lower or comparable to those of MS galaxies in the inner region. These trends indicate that enhanced SFE contributes to higher $\Delta$MS values, whereas reduced $f_{\mathrm{gas}}$ results in lower $\Delta$MS values. The less prominent bulge or the presence of a bar structure in UMS galaxies induces disk-wide star formation, consequently increasing the SFE. In LMS galaxies, the molecular gas is exhausted, and their star formation activity is low. Environmental effects, such as tidal gas stripping, may also reduce gas supply from the outer regions. Furthermore, our sample galaxies show that both the specific star formation rate (sSFR) and $f_{\mathrm{gas}}$ decrease in the central region in LMS galaxies but did not change in the same region in UMS galaxies. These results seem to support the inside-out quenching of star formation although the dominant cause of depletion remains uncertain.