Gas-to-dust ratios in massive star-forming galaxies at z similar to 1.4

摘要

We present results of (CO)-C-12(J = 2-1) observations toward four massive star-forming galaxies at z similar to 1.4 with the Nobeyama 45m radio telescope. The galaxies are detected with Spitzer/MIPS in 24 mu m and Herschel/SPIRE in 250 mu m and 350 mu m, and they mostly reside in the main sequence. Their gas-phase metallicities derived by the N2 method using the H alpha and [NII]lambda 6584 emission lines are near the solar value. CO lines are detected toward three galaxies. The molecular-gas masses obtained are (9.6-35) x 10(10) M-circle dot by adopting the Galactic CO-to-H-2 conversion factor and a CO(2-1)/CO(1-0) flux ratio of 3. The dust masses derived from the modified blackbody model (assuming a dust temperature of 35K and an emissivity index of 1.5) are (2.4-5.4) x 10(8) M-circle dot. Resulting gas-to-dust ratios (not accounting for HI mass) at z similar to 1.4 are 220-1450, which are several times larger than those in local star-forming galaxies. A dependence of the gas-to-dust ratio on the far-infrared luminosity density is not clearly seen.