Metals in Star-Forming Galaxies with KCWI. I. Methodology and First Results on the Abundances of Iron, Magnesium, and Oxygen
Zhuyun Zhuang, Evan N. Kirby, Charles C. Steidel, Mithi A. C. de los Reyes, Nikolaus Z. Prusinski, N. Leethochawalit, Minjung Park, Charlie Conroy, Evan H. Nuñez
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36 pages, 16 figures, 4 tables; accepted for publication in ApJ. Main results in Figure 7, 10 and 11
Understanding the chemical enrichment of different elements is crucial to gaining a complete picture of galaxy chemical evolution. In this study, we present a new sample of 46 low-redshift, low-mass star-forming galaxies at $M_*\sim 10^{8-10}M_{\odot}$ along with two quiescent galaxies at $M_*\sim 10^{8.8}M_{\odot}$ observed with the Keck Cosmic Web Imager (KCWI), aiming to investigate the chemical evolution of galaxies in the transition zone between Local Group satellites and massive field galaxies. We develop a novel method to simultaneously determine stellar abundances of iron and magnesium in star-forming galaxies. With the gas-phase oxygen abundance (O/H)$_{\rm g}$ measured using the strong line method, we are able to make the first-ever apples-to-apples comparison of $α$ elements in the stars and the ISM. We find that the [Mg/H]$_*$-[O/H]$_{\rm g}$ relation is much tighter than the [Fe/H]$_*$-[O/H]$_{\rm g}$ relation, which can be explained by the similar production processes of $α$ elements. Most galaxies in our sample exhibit higher [O/H]$_{\rm g}$ than [Fe/H]$_*$ and [Mg/H]$_*$. In addition, we construct mass-metallicity relations (MZRs) measured as three different elements (Fe$_*$, Mg$_*$, O$_{\rm g}$). Compared to the gas O-MZR, the stellar Fe- and Mg-MZRs show larger scatter driven by variations in specific star formation rates (sSFR), with star-forming galaxies exhibiting higher sSFR and lower stellar abundances at fixed mass. The excess of [O/H]$_{\rm g}$ compared to stellar abundances as well as the anti-correlation between sSFR and stellar abundance suggests that galaxy quenching of intermediate-mass galaxies at $M_*\sim 10^{8-10}M_{\odot}$ is primarily driven by starvation.
High Radiation Pressure on Interstellar Dust Computed by Light-Scattering Simulation on Fluffy Agglomerates of Magnesium-silicate Grains with Metallic-iron Inclusions
The Mysterious Case of Iron in XMPs: Anomalous High log(Fe/O) Observed in Extremely Metal-Poor Galaxies HSCJ1631+4426 and SDSSJ0811+4730
Swinburne University of Technology（斯威本科技大学）；The University of Sydney（悉尼大学）；University of Queensland（昆士兰大学）；University of Western Australia（西澳大学）；Astronomy Australia Ltd.（澳大利亚天文学有限公司）；The University of Oklahoma（俄克拉荷马大学）
The complex stellar system M 22: constraining the chemical enrichment from AGB stars using magnesium isotope ratios
Research School of Astronomy & Astrophysics, Australian National University（澳大利亚国立大学天文与天体物理研究学院）；ARC Centre of Excellence for Astrophysics in Three Dimensions (ASTRO-3D)（三维天体物理学卓越研究中心（ASTRO-3D））；School of Physics & Astronomy, Monash University（蒙纳士大学物理与天文学院）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；Istituto Nazionale di Astrofisica — Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；Istituto Nazionale di Astrofisica — Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切尔天文台）
A Theoretical Study of the Stellar Parameters and Surface Nucleosynthesis of the Extremely Metal-Poor RGB Giant BD$-18^{\circ}$5550 - Part I: Effects of $α$-enhancement and Internal Mixing
