Properties of Molecular Gas in Star-Forming Galaxies at z ∼ 1.4 with ALMA

We made CO(J=5-4) observations of 20 star-forming galaxies at z similar to 1.4 with ALMA to study properties of molecular gas with respect to the stellar mass and metallicity. Almost all of our sample galaxies are on the main sequence of star forming galaxies at this redshift. Uniqueness of the sample is gas phase metallicity is known for each galaxy. The metallicities of our sample galaxies are derived from near-infrared spectroscopic observations with Subaru/FMOS. The ranges of metallicity (12+log(O/H)) and stellar mass are 8.2-8.9 and 4 x 10(9)-4 x 10(11) M-circle dot, respectively. The stellar mass range covers lower mass than that in previous studies. We detected CO emission lines from 11 galaxies. Molecular gas mass is derived by adopting metallicity-dependent CO-to-H-2 conversion factor. The derived molecular gas masses of detected galaxies are (3-11)x10(10) M-circle dot. The molecular gas mass fractions are 0.25-0.94, and the fraction is lower in a more massive galaxy or a galaxy with higher metallicity. However, it is difficult to conclude which of stellar mass and metallicity is a main cause for the relations. We try to constrain the inflow and outflow rate by using an analytic chemical evolution model.