Dust continuum, CO, and [C I] 1-0 lines: self-consistent H2 mass
  estimates and the possibility of globally CO-dark galaxies at $z = 0.35$
  We present ALMA observations of a small but statistically complete sample of
twelve 250 micron selected galaxies at $z=0.35$ designed to measure their dust
submillimeter continuum emission as well as their CO(1-0) and atomic carbon
[CI](3P1-3P0) spectral lines. This is the first sample of galaxies with global
measures of all three $H_2$-mass tracers and which show star formation rates
(4-26 Msun yr$^{-1}$) and infra-red luminosities ($1-6\times10^{11}$ Lsun)
typical of star forming galaxies in their era. We find a surprising diversity
of morphology and kinematic structure; one-third of the sample have evidence
for interaction with nearby smaller galaxies, several sources have disjoint
dust and gas morphology. Moreover two galaxies have very high $L_{CI}/L_{CO}$
ratios for their global molecular gas reservoirs; if confirmed, such extreme
intensity ratios in a sample of dust selected, massive star forming galaxies
presents a challenge to our understanding of ISM. Finally, we use the emission
of the three molecular gas tracers, to determine the carbon abundance,
$X_{ci}$, and CO-$\rm{H_2}$ conversion $\alpha_{co}$ in our sample, using a
weak prior that the gas-to-dust ratio is similar to that of the Milky Way for
these massive and metal rich galaxies. Using a likelihood method which
simultaneously uses all three gas tracer measurements, we find mean values and
errors on the mean of
$\alpha_{co}=3.0\pm0.5\,\rm{Msun\,(K\,kms^{-1}\,pc^2)^{-1}}$ and
$X_{ci}=1.6\pm0.1\times 10^{-5}$ (or $\alpha_{ci}=18.8\,K kms^{-1}\,pc^2
(Msun)^{-1}$) and $\delta_{GDR}=128\pm16$ (or
$\alpha_{850}=5.9\times10^{12}\,\rm{W\,Hz^{-1}\, Msun^{-1}}$), where our
starting assumption is that these metal rich galaxies have an average
gas-to-dust ratio similar to that of the Milky Way centered on
$\delta_{GDR}=135$.
