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 Valparaiso 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 >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) x 10(10) K km s(-1) pc(2), equivalent to log(M-gas/M-circle dot) = 8.9-10.9 assuming an alpha(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 similar to 3.5 arcsec resolution (6.5 kpc), finding that the molecular gas is on average similar to 0.6 times more compact than the stellar component. We obtain a global Schmidt-Kennicutt relation, given by log[Sigma(SFR)/(M(circle dot)yr(-1)kpc(-2))] = (1.26 +/- 0.02) x log[Sigma(MH2)/(M(circle dot)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 L-IR = 10(11-12) L-circle dot. 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 x (log L-IR -11.45) - 8.26 - 0.41 x arctan[-4.84 (lo gL(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.