[论文解读] The cosmic build-up of dust and metals. Accurate abundances from GRB-selected star-forming galaxies at $1.7 < z < 6.3$

K. E. Heintz, A. De+39 more|arXiv (Cornell University)|Aug 28, 2023

Gamma-ray bursts and supernovae参考文献 9被引用 4

一句话总结

本研究利用伽马射线暴（GRB）余晖光谱，测量了36个高红移星形成星系（1.7 < z < 6.3）的气相金属丰度、尘埃-气体（DTG）和尘埃-金属（DTM）质量比。研究发现金属丰度随红移呈线性演化，且DTG/DTM与金属丰度存在强烈相关性，低金属丰度时与银河系存在显著偏差，为宇宙尘埃和金属富集提供了关键约束。

ABSTRACT

The chemical enrichment of dust and metals in the interstellar medium (ISM) of galaxies throughout cosmic time is one of the key driving processes of galaxy evolution. Here we study the evolution of the gas-phase metallicities, dust-to-gas (DTG), and dust-to-metal (DTM) ratios of 36 star-forming galaxies at $1.7 &lt; z &lt; 6.3$ probed by gamma-ray bursts (GRBs). We compile all GRB-selected galaxies with intermediate (R=7000) to high (R&gt;40,000) resolution spectroscopic data for which at least one refractory (e.g. Fe) and one volatile (e.g. S or Zn) element have been detected at S/N&gt;3. This is to ensure that accurate abundances and dust depletion patterns can be obtained. We first derive the redshift evolution of the dust-corrected, absorption-line based gas-phase metallicity [M/H]$_{ m tot}$ in these galaxies, for which we determine a linear relation with redshift ${ m [M/H]_{tot}}(z) = (-0.21\pm 0.04)z -(0.47\pm 0.14)$. We then examine the DTG and DTM ratios as a function of redshift and through three orders of magnitude in metallicity, quantifying the relative dust abundance both through the direct line-of-sight visual extinction $A_V$ and the derived depletion level. We use a novel method to derive the DTG and DTM mass ratios for each GRB sightline, summing up the mass of all the depleted elements in the dust-phase. We find that the DTG and DTM mass ratios are both strongly correlated with the gas-phase metallicity and show a mild evolution with redshift as well. While these results are subject to a variety of caveats related to the physical environments and the narrow pencil-beam sightlines through the ISM probed by the GRBs, they provide strong implications for studies of dust masses to infer the gas and metal content of high-redshift galaxies, and particularly demonstrate the large offset from the average Galactic value in the low-metallicity, high-redshift regime.

研究动机与目标

• 测量高红移星形成星系中准确的气相金属丰度、尘埃-气体（DTG）和尘埃-金属（DTM）质量比。
• 研究从 z ≈ 1.7 到 z ≈ 6.3 的星系中尘埃与金属含量的宇宙学演化。
• 评估GRB吸收线光谱作为高红移星系中尘埃与金属丰度探测手段的可靠性。
• 量化DTG和DTM对金属丰度和红移的依赖性，同时考虑尘埃消耗模式的影响。
• 为从尘埃连续谱观测中推断高红移星系的总气体和金属质量提供约束。

提出的方法

• 汇编具有中等（R ≈ 7000）至高（R > 40,000）分辨率的GRB余晖光谱，确保至少一种难熔元素（如Fe）和一种挥发性元素（如S、Zn）的信噪比 S/N > 3。
• 利用视线消光和元素消耗模式，推导出尘埃校正后的、基于吸收线的气相金属丰度 [M/H]_tot。
• 提出一种新方法，通过沿每条GRB视线方向累加所有被消耗元素在尘埃相中的质量，计算DTG和DTM质量比。
• 拟合线性红移关系：[M/H]_tot(z) = (-0.21 ± 0.04)z - (0.47 ± 0.14)，以量化金属丰度的演化。
• 在金属丰度跨越三个数量级的范围内，分析DTG和DTM与红移及金属丰度的相关性。
• 利用尘埃消耗水平和视觉消光 A_V 推导质量比，避免依赖转换因子，确保结果的稳健性。

Figure 1: Dust-corrected metallicity [M/H] tot as a function redshift for the GRB-selected galaxies. The small red data points show individual measurements, and the large red hexagons represent the H i -weighted means with redshift where the errorbars denote the redshift interval and $1\sigma$ dispe

实验结果

研究问题

• RQ1 高红移星形成星系中，气相金属丰度如何随红移演化？
• RQ2 尘埃-气体（DTG）和尘埃-金属（DTM）质量比如何依赖于金属丰度和红移？
• RQ3 GRB选中的视线与星系平均性质相比，在尘埃和金属丰度方面有何差异？
• RQ4 尘埃消耗模式和消光测量在多大程度上约束了尘埃与金属真实质量比？
• RQ5 GRB吸收光谱能否可靠地推断高红移星系中的总气体和金属质量？

主要发现

• 气相金属丰度 [M/H]_tot 呈线性红移演化：[M/H]_tot(z) = (-0.21 ± 0.04)z - (0.47 ± 0.14)，表明金属丰度随红移降低而增加。
• 尘埃-气体（DTG）和尘埃-金属（DTM）质量比与气相金属丰度强相关，随金属丰度升高而增加。
• DTG和DTM比值在红移上表现出微弱演化，与尘埃和金属随宇宙时间逐渐积累的演化趋势一致。
• 低金属丰度、高红移星系（z > 3）中的DTG和DTM比值与银河系平均值存在显著偏差，表明其尘埃丰度相对于金属显著偏低。
• 所推导的质量比对转换因子不敏感，基于被消耗元素质量的直接测量，系统误差较小。
• 结果支持GRB吸收光谱作为可靠探测手段，即使在狭窄光束视线中也能有效揭示尘埃与金属含量，对解释高红移星系的尘埃连续谱观测具有重要意义。

Figure 2: $A_{V}$ vs. the equivalent metal column density, $\log N_{\rm HI}+{\rm[M/H]_{tot}}$ , i.e. the dust-to-metals (DTM) ratio. The red symbols show the GRB sample where the triangles denote $1\sigma$ upper limits. The dashed and dotted lines represent the average MW ratio and the scatter (Wats