Vales I: The Molecular Gas Content In Star-Forming Dusty H-Atlas Galaxies Up To Z=0.35

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 >5σ significance and 12 others are seen at low significance in stacked spectra. CO luminosities are in the range of (0.03 − 1.31) × 1010 K km s−1 pc2, equivalent to log (Mgas/M⊙) = 8.9 − 10.9 assuming an αCO = 4.6 (K km s−1 pc2)−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 ∼3 \n′′. \n.′′ \n \n5 resolution (6.5 kpc), finding that the molecular gas is on average ∼ 0.6 times more compact than the stellar component. We obtain a global Schmidt-Kennicutt relation, given by \nlog[ΣSFR/(M⊙yr−1kpc−2)]=(1.26±0.02)×log[ΣMH2/(M⊙pc−2)]−(3.6±0.2) \nlog⁡[ΣSFR/(M⊙yr−1kpc−2)]=(1.26±0.02)×log⁡[ΣMH2/(M⊙pc−2)]−(3.6±0.2) \n. 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 \nLIR=1011−12L⊙ \nLIR=1011−12L⊙ \n.Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parameterised by \nlog[SFR/MH2]=0.19×(logLIR−11.45)−8.26−0.41×arctan[−4.84(logLIR−11.45)] \nlog[SFR/MH2]=0.19×(logLIR−11.45)−8.26−0.41×arctan⁡[−4.84(log⁡LIR−11.45)] \n. Within the redshift range we explore (z < 0.35), we identify a rapid increase of the gas content as a function of redshift.