Oral Presentation
Molecular gas properties in star-forming galaxies at z~1.4 with ALMA
Revealing the properties of molecular gas in high redshift galaxies is crucial for the understanding of galaxy formation and evolution. We made CO(5-4) observations of 20 star-forming galaxies at z~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 that gas metallicity is known for each galaxy. The metallicities of our sample galaxies are derived from near-infrared observations with Subaru/FMOS. The ranges of metallicity (12+log(O/H)) and stellar mass (Salpeter IMF) are 8.1-8.8 and 4x10^9-4x10^11 Msun, respectively. The stellar mass range covers a lower mass than that in previous studies. We detected CO emission lines from about half of the galaxies. Molecular gas mass is derived by adopting metallicity dependence of CO-to-H2 conversion factor. The molecular gas mass fractions of detected galaxies are 0.3-0.8, and the fraction is lower in a more massive galaxy. Stacking analysis also shows the same trend. Meanwhile, the stacking analysis shows the molecular gas fraction does not depend on the metallicity at a fixed stellar mass significantly.
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