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 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 themolecular 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 ~3.5 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[ΣSFR/(M⊙ yr-1 kpc-2)] = (1.26 ± 0.02) × log[ΣMH2/(M⊙ pc-2)] - (3.6 ± 0.2).We find a significant fraction of galaxies lying at 'intermediate efficiencies' between a longstanding mode of star formation activity and a starburst, specially at LIR = 1011-12 L⊙. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parametrized by log [SFR/MH2] = 0.19 × (log LIR - 11.45) - 8.26-0.41 × arctan[-4.84 (logLIR - 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.