Constraint on the Gas-to-Dust Ratio in Massive Star-Forming Galaxies at
  z~1.4
  We carried out 12CO(J=2-1) observations toward three star-forming galaxies on
the main sequence at z~1.4 with the Nobeyama 45m radio telescope. These
galaxies are detected with Spitzer/MIPS in 24 um, Herschel/SPIRE in 250 um and
350 um, and their gas metallicity, derived from optical emission line ratios
based on near infrared spectroscopic observations, is close to the solar
metallicity. Although weak signal-like features of CO were seen, we could not
detect significant CO emission. The dust mass and the upper limits on the
molecular gas mass are (3.4-6.7) x 10^{8} Msun and (9.7-14) x 10^{10} Msun,
respectively. The upper limits on the gas-to-dust ratios at z~1.4 are 150-410
which are comparable to the gas-to-dust ratios in local galaxies with similar
gas metallicity. A line stacking analysis enables us to detect a significant CO
emission and to derive an average molecular gas mass of 1.3 x 10^{11} Msun and
gas-to-dust ratio of 250. This gas-to-dust ratio is also near that in local
galaxies with solar metallicity. These results suggest that the gas-to-dust
ratio in star-forming galaxies with solar metallicity does not evolve
significantly up to z~1.4. By comparing to a theoretical calculation, a rapid
increase of the dust mass in an earlier epoch of galaxy evolution is suggested.
