The MaNGA Low-mass disks HUnt for CO (MaLHUCO) Survey

TL;DR

This study uses JCMT observations to analyze molecular gas in low-mass, star-forming disk galaxies, revealing correlations with star formation and interstellar medium properties, and testing scaling relations.

Contribution

First systematic CO(2-1) survey of low-mass, late-type galaxies from MaNGA, exploring molecular gas content and its relation to star formation and galaxy evolution.

Findings

CO detected in 55% of the sample.

12 μm luminosity correlates linearly with CO emission.

The Kennicutt-Schmidt law remains linear at low stellar masses.

Abstract

We present James Clerk Maxwell Telescope (JCMT) observations of the $^{12}$CO(J = 2-1) emission of 42 low-mass, star-forming disk galaxies of morphological type Scd or later from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. The sample, which probes the M33-like stellar-mass regime, is complemented with metallicities, star formation rates, and \hi\ masses used to investigate the star formation process and to test scaling relations involving molecular gas mass in low-mass systems. We detect CO emission in 55% of the sample and derive H$_2$ masses using both a constant Galactic and a metallicity-dependent CO-to-H$_2$ conversion factor. The 12 $\mu$m luminosity, which includes polycyclic aromatic hydrocarbon features, exhibits a tight linear correlation with the CO line emission, making it a robust tracer of global molecular gas content. The molecular gas mass - star formation rate relation, i.e. the Kennicutt-Schmidt law, is the most fundamental one and it is found to remain linear down to low stellar masses. We also find that the mean molecular gas depletion time is slightly shorter in low-mass late-type galaxies than in more massive systems, consistent with their higher specific star formation rates. Finally, while the specific molecular gas mass ($M_{\rm H_2}/M_*$) shows no significant dependence on stellar mass and a large intrinsic scatter, the HI-to-stellar mass ratio ($M_{\rm HI}/M_*$) decreases with increasing stellar mass and molecular fraction ($M_{\rm H_2}/M_{\rm gas}$), highlighting the progressive transition from atomic- to molecular-dominated interstellar medium along the galaxy population.