We carried out ^ { 12 } CO ( J = 2 - 1 ) observations toward three star-forming galaxies on the main sequence at z \sim 1.4 with the Nobeyama 45m radio telescope .
These galaxies are detected with Spitzer /MIPS in 24 \mu \mathrm { m } , Herschel /SPIRE in 250 \mu \mathrm { m } and 350 \mu \mathrm { m } , 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 ) \times 10 ^ { 8 } M _ { \odot } and ( 9.7 - 14 ) \times 10 ^ { 10 } ( \alpha _ { \mathrm { CO } } / 4.36 ) M _ { \odot } , respectively .
The upper limits on the gas-to-dust ratios at z \sim 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 \times 10 ^ { 11 } M _ { \odot } 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 \sim 1.4 .
By comparing to a theoretical calculation , a rapid increase of the dust mass in an earlier epoch of galaxy evolution is suggested .