VALES: I. The molecular gas content in star-forming dusty H-ATLAS galaxies up to 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 Valparaíso 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 $(0.03-1.31)\times 10^{10}$ K km s${}^{-1}$ pc${}^2$, equivalent to $\log ({\mathrm{M}}_{\mathrm{gas}}/{\mathrm{M}}_{\odot })=8.9-10.9$ assuming an ${\alpha }_{\mathrm{CO}}$=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 $\log [{\Sigma }_{\mathrm{SFR}}/({\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}\mathrm{kp}{\mathrm{c}}^{-2})]=(1.26\pm 0.02)\times \log [{\Sigma }_{{\mathrm{M}}_{H2}}/({\mathrm{M}}_{\odot }\mathrm{p}{\mathrm{c}}^{-2})]-(3.6\pm 0.2)$. 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 ${\mathrm{L}}_{\mathrm{IR}}=10^{11-12}{\mathrm{L}}_{\odot }$. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parameterised by $\log [SFR/{\mathrm{M}}_{H2}]=0.19\times (\log {\mathrm{L}}_{\mathrm{IR}}-11.45)-8.26-0.41\times \arctan [-4.84(\log {\mathrm{L}}_{\mathrm{IR}}-11.45)]$. Within the redshift range we explore ($z<0.35$), we identify a rapid increase of the gas content as a function of redshift.

Accepted for publication in MNRAS. 31 pages, including 9 figures and 2 tables

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