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 characterize 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(M_gas/M⊙)=8.9--10.9 assuming an α_CO = 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 ∼3.5 arcsec 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 log[Σ_SFR/(M⊙yr⁻¹kpc⁻²)]=(1.26±0.02)×log[ΣM_H2/(M⊙pc⁻²)]−(3.6±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 LIR = 10^11–12 L⊙. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parametrized by log[SFR/M_H2]=0.19×(logL_IR−11.45)−8.26−0.41 × arctan[−4.84(logL_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.