VALES: I. The molecular gas content in star-forming dusty H-ATLAS galaxies up to z=0.35

TL;DR

This study uses ALMA observations to analyze the molecular gas content and star formation efficiency in 67 dusty star-forming galaxies up to redshift 0.35, revealing insights into galaxy evolution and gas dynamics.

Contribution

It provides the first detailed molecular gas measurements for a large sample of nearby dusty galaxies, expanding understanding of star formation and gas properties at low redshift.

Findings

Molecular gas is on average 0.6 times more compact than stellar component.

Established a global Schmidt-Kennicutt relation for the sample.

Identified a rapid increase in gas content with redshift within z<0.35.

Abstract

We present an extragalactic survey using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) to characterise galaxy populations up to $z=0.35$: the Valpara\'iso ALMA Line Emission Survey (VALES). We use ALMA Band-3 CO(1--0) observations to study the molecular gas content in a sample of 67 dusty normal star-forming galaxies selected from the $Herschel$ Astrophysical Terahertz Large Area Survey ($H$-ATLAS). We have spectrally detected 49 galaxies at $>5\sigma$ significance and 12 others are seen at low significance in stacked spectra. CO luminosities are in the range of $(0.03-1.31)\times10^{10}$ K km s$^{-1}$ pc$^2$, equivalent to $\log({\rm M_{gas}/M_{\odot}}) =8.9-10.9$ assuming an $\alpha_{\rm CO}$=4.6(K km s$^{-1}$ pc$^{2}$)$^{-1}$, which perfectly complements the parameter space previously explored with local and high-z normal galaxies. We compute the optical to CO size ratio for 21 galaxies resolved by ALMA at $\sim 3$."$5$ resolution (6.5 kpc), finding that the molecular gas is on average $\sim$ 0.6 times more compact than the stellar component. We obtain a global Schmidt-Kennicutt relation, given by $\log [\Sigma_{\rm SFR}/({\rm M_{\odot} yr^{-1}kpc^{-2}})]=(1.26 \pm 0.02) \times \log [\Sigma_{\rm M_{H2}}/({\rm M_{\odot}\,pc^{-2}})]-(3.6 \pm 0.2)$. We find a significant fraction of galaxies lying at `intermediate efficiencies' between a long-standing mode of star-formation activity and a starburst, specially at $\rm L_{IR}=10^{11-12} L_{\odot}$. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parameterised by $\log [{\rm SFR/M_{H2}}]=0.19 \times {\rm (\log {L_{IR}}-11.45)}-8.26-0.41 \times \arctan[-4.84 (\log {\rm L_{IR}}-11.45) ]$. Within the redshift range we explore ($z<0.35$), we identify a rapid increase of the gas content as a function of redshift.