The chemical enrichment in the early Universe as probed by JWST via direct metallicity measurements at z ~ 8
The chemical enrichment in the early Universe as probed by JWST via direct metallicity measurements at z ~ 8
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JWST 通过 z ~ 8 处的直接金属丰度测量探测到早期宇宙的化学富集
DOI：
10.1093/mnras/stac2737
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发表时间：
2023
影响因子：
4.8
通讯作者：
Curti M
中科院分区：
文献类型：
--
作者：
Curti M
强星云发射线是追踪恒星形成星系在宇宙时间内演化的重要诊断工具。然而，不同的观测装置会影响这些谱线，也会影响星云物理性质的推导。我们分析了来自COS遗留光谱调查（CLASSY）的12个本地恒星形成星系，以评估使用不同孔径组合对确定物理条件和气相金属丰度的影响。我们将观测到的光谱与斯隆数字巡天数据释放孔径进行了比较，该孔径直径为3英寸，与COS、IFU和长缝光谱相似，包括对五个CLASSY星系的新LBT/MODS观测。我们计算了变红、电子密度和温度、金属丰度、恒星形成速率和等效宽度（EWs）。我们发现电子密度、温度和金属丰度的测量值与孔径大小大致保持不变，表明该样品的气体条件相对均匀。然而，利用IFU对三个星系的观测，我们发现由Balmer比值得出的E （B−V）值随着孔径的增大而减小（高达53%）。这些数值在星系中心变化最为显著，在COS孔径为2 farcs 5附近趋于平稳。我们使用Hα和[O iii] λ5007 EWs作为孔径光分数的函数来研究气体和恒星的相对贡献，但发现在给定星系内几乎没有变化。这些结果表明，光学光谱提供了适合于远紫外CLASSY光谱的星云性质，即使使用窄视场0长狭缝观测。
Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the Sloan Digital Sky Survey Data Release aperture, which has a 3''diameter similar to COS, IFU, and long-slit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using IFU observations of three galaxies, we find that the E (B− V) values derived from the Balmer ratios decrease (by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2 farcs 5. We examine the relative contributions from the gas and stars using the Hα and [O iii] λ5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the far-UV CLASSY spectra, even when narrow 1 farcs 0 long-slit observations are used.