Constraint on the inflow/outflow rates in star-forming galaxies at z~1.4 from molecular gas observations

We constrain the rate of gas inflow into and outflow from a main-sequence star-forming galaxy at z~1.4 by fitting a simple analytic model for the chemical evolution in a galaxy to the observational data of the stellar mass, metallicity, and molecular gas mass fraction. The molecular gas mass is derived from CO observations with a metallicity-dependent CO-to-H2 conversion factor, and the gas metallicity is derived from the H{\alpha} and [NII]{\lambda} 6584 emission line ratio. Using a stacking analysis of CO integrated intensity maps and the emission lines of H{\alpha} and [NII], the relation between stellar mass, metallicity, and gas mass fraction is derived. We constrain the inflow and outflow rates with least-chi-square fitting of a simple analytic chemical evolution model to the observational data. The best-fit inflow and outflow rates are ~1.7 and ~0.4 in units of star-formation rate, respectively. The inflow rate is roughly comparable to the sum of the star-formation rate and outflow rate, which supports the equilibrium model for galaxy evolution; i.e., all inflow gas is consumed by star formation and outflow.Comment: 5 pages, 2 figures, Accepted for publication in the Ap

銀河進化の激動期における星形成銀河の星間物質の研究

京都大学0048新制・課程博士博士(理学)甲第20180号理博第4265号新制||理||1613(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 太田 耕司, 准教授 栗田 光樹夫, 教授 長田 哲也学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA

Constraint on the gas-to-dust ratio in massive star-forming galaxies at z ∼ 1.4

We carried out [12]CO (J = 2–1) observations toward three star-forming galaxies on the main sequence at z ∼ 1.4 with the Nobeyama 45 m radio telescope. These galaxies have been detected with Spitzer/MIPS in 24 μm, Herschel/SPIRE in 250 μm and 350 μm; 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) × 10[8] M⊙ and (9.7–14) × 10[10] (αCO/4.36) M⊙, 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 significant CO emission and to derive an average molecular gas mass of 1.3 × 10[11] M⊙and gas-to-dust ratio of 250. This gas-to-dust ratio is also near to 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

First-Principles Selection of Solute Elements for Er-Stabilized Bi₂O₃ Oxide-Ion Conductor with Improved Long-Term Stability at Moderate Temperatures

Quality oxide-ion conductors are essential for clean-energy applications. Rare-earth-stabilized bismuth sesquioxide, δ-Bi₂O₃, exhibits a much greater oxide-ion conductivity at high temperatures than commonly used ZrO₂- or CeO₂-based electrolytes, but it suffers from serious conductivity degradation while annealing at moderate temperatures of ∼773 K, which is the target temperature for many applications. Here, we demonstrate that a novel set of solute elements for δ-Bi₂O₃ can significantly enhance the long-term stability at 773 K. A pure oxide-ion conductivity of 0.035 S/cm at 773 K remains unchanged during annealing for 100 h, which is five times greater than the best known solid-state oxide materials after long-term annealing. For materials design, we explore a range of chemical spaces using theoretical methods based on first-principles calculations. The order–disorder transition temperature of the anion sublattice, oxygen-ion diffusivity, and solution free energy are used as descriptors. The design concept is verified experimentally