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 Valpara\'iso 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
$(0.03-1.31)\times10^{10}$ K km s$^{-1}$ pc$^2$, equivalent to $\log({\rm
M_{gas}/M_{\odot}}) =8.9-10.9$ assuming an $\alpha_{\rm CO}$=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 $\log [\Sigma_{\rm SFR}/({\rm M_{\odot}
yr^{-1}kpc^{-2}})]=(1.26 \pm 0.02) \times \log [\Sigma_{\rm M_{H2}}/({\rm
M_{\odot}\,pc^{-2}})]-(3.6 \pm 0.2)$. 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 $\rm L_{IR}=10^{11-12}
L_{\odot}$. Combining our observations with data taken from the literature, we
propose that star formation efficiencies can be parameterised by $\log [{\rm
SFR/M_{H2}}]=0.19 \times {\rm (\log {L_{IR}}-11.45)}-8.26-0.41 \times
\arctan[-4.84 (\log {\rm L_{IR}}-11.45) ]$. Within the redshift range we
explore ($z<0.35$), we identify a rapid increase of the gas content as a
function of redshift.
