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arXiv 1912.02201astro-ph.GA
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恒星形成取样效应对用$\textit{JWST}$探测的透镜$z>6$星系光谱的影响

The impact of star formation sampling effects on the spectra of lensed $z>6$ galaxies detectable with $\textit{JWST}$

Anton Vikaeus, Erik Zackrisson, Christian Binggeli

摘要:

即将进行的$\textit{James Webb Space Telescope}$($\textit{JWST}$)将允许在比以往任何时候都更微弱的探测水平上观测高红移星系,而针对引力透镜场的$\textit{JWST}$巡天预计将使恒星形成率非常低的$z\gtrsim 6$天体进入光谱研究的范围。随着越来越低的恒星形成活动的星系被纳入视野,许多用于分析综合星系光谱的标准方法在某些时候必然会崩溃,这是由于违反了良好采样的恒星初始质量函数(IMF)和缓慢变化的SFR的假设。我们认为,星系与SFR $\sim 0.1\ M_\odot$年$^{-1}$可能会出现在光谱检测限的$\textit{JWST}$在透镜领域,并调查在何种程度上恒星形成采样可能会影响光谱分析等对象。我们使用的$\small{\text{SLUG}}$光谱合成代码来证明,这样的效果很可能有显着的影响,例如,巴耳末发射线的光谱诊断。这些影响被发现主要源于SFR迅速变化的短($\sim$百万年)的时间尺度,由于恒星形成在有限的单位(星团),而一个采样不足的国际货币基金组织的影响被认为是微不足道的比较。与此相反,HeII和HI电离通量之间的比率被认为是敏感的IMF采样以及ICMF采样(初始集群质量函数的采样),这可能会影响解释的星系包含人口III恒星或其他来源的硬电离辐射。

英文摘要:

The upcoming $\textit{James Webb Space Telescope}$ ($\textit{JWST}$) will allow observations of high-redshift galaxies at fainter detection levels than ever before, and $\textit{JWST}$ surveys targeting gravitationally lensed fields are expected to bring $z\gtrsim 6$ objects with very low star formation rate (SFR) within reach of spectroscopic studies. As galaxies at lower and lower star formation activity are brought into view, many of the standard methods used in the analysis of integrated galaxy spectra are at some point bound to break down, due to violation of the assumptions of a well-sampled stellar initial mass function (IMF) and a slowly varying SFR. We argue that galaxies with SFR$\sim 0.1\ M_\odot$ yr$^{-1}$ are likely to turn up at the spectroscopic detection limit of $\textit{JWST}$ in lensed fields, and investigate to what extent star formation sampling may affect the spectral analysis of such objects. We use the $\small{\text{SLUG}}$ spectral synthesis code to demonstrate that such effects are likely to have significant impacts on spectral diagnostics of, for example, the Balmer emission lines. These effects are found to stem primarily from SFRs varying rapidly on short ($\sim$ Myr) timescales due to star formation in finite units (star clusters), whereas the effects of an undersampled IMF is deemed insignificant in comparison. In contrast, the ratio between the HeII- and HI-ionizing flux is found to be sensitive to IMF-sampling as well as ICMF-sampling (sampling of the initial cluster mass function), which may affect interpretations of galaxies containing Population III stars or other sources of hard ionizing radiation.

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