Dust, Gas, and Metal Content in Star-forming Galaxies at z ∼ 3.3 Revealed with ALMA and Near-IR Spectroscopy
We conducted submillimeter observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of star-forming galaxies at z ∼ 3.3, whose gas-phase metallicities have been measured previously. We investigated the dust and gas contents of the galaxies at z ∼ 3.3 and studied the interaction of galaxies with their circumgalactic or intergalactic medium at this epoch by probing their gas mass fractions and gas-phase metallicities. Single-band dust continuum emission tracing dust mass and the relation between the gas-phase metallicity and gas-to-dust mass ratio were used to estimate the gas masses. The estimated gas mass fractions and depletion timescales are f gas= 0.20–0.75 and t dep= 0.09–1.55 Gyr. Although the galaxies appear to be tightly distributed around the star-forming main sequence at z ∼ 3.3, both quantities show a wider spread at a fixed stellar mass than expected from the scaling relation, suggesting a large diversity of fundamental gas properties in star-forming galaxies that apparently lie on the main sequence. When we compared gas mass fraction and gas-phase metallicity in star-forming galaxies at z ∼ 3.3 and at lower redshifts, star-forming galaxies at z ∼ 3.3 appear to be more metal poor than local galaxies with similar gas mass fractions. Using the gas regulator model to interpret this offset, we find that this can be explained by a higher mass-loading factor, suggesting that the mass-loading factor in outflows increases at earlier cosmic times.