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arXiv 2301.07072astro-ph.GA
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利用CEERS进行的JWST/NIRSpec对z=7-9恒星形成星系的光谱观测:对电离泡中明亮Lyα发射体的新认识

JWST/NIRSpec Spectroscopy of $z=7-9$ Star Forming Galaxies with CEERS: New Insight into Bright Ly$α$ Emitters in Ionized Bubbles

Mengtao Tang, Daniel P. Stark, Zuyi Chen, Charlotte Mason, Michael Topping, Ryan Endsley, Peter Senchyna, Adèle Plat, Ting-Yi Lu, Lily Whitler, Brant Robertson, Stéphane Charlot

AI总结:

本文利用CEERS巡天的JWST/NIRSpec数据研究z≳7星系,发现Lyα发射体具有极端电离和低金属丰度特征,其Lyα发射比低红移样本弱6-12倍,表明它们可能位于小型电离泡中。

摘要:

我们描述了来自CEERS巡天的对z≳7星系的新JWST/NIRSpec观测。该区域先前的观测揭示了在红移z=7.5、7.7、8.7处Lyα发射体的成协现象,而这些红移处星际介质(IGM)被认为大部分是中性,这导致人们提出这些系统位于大型电离泡中。我们在CEERS数据集中识别出21个具有可靠红移的z≳7星系,其中包括10个位于Lyα成协中的星系。它们的光谱表明气体高度电离且金属贫乏,具有在较低红移处很少见到的谱线比(O32=17.84和Ne3O2=0.89,线性标度)和金属丰度(12+log(O/H)=7.84)。我们发现样本中六个z≳7 Lyα发射体具有最极端的谱线性质。每个都具有硬电离谱,表明它们的可见性可能因高效的电离光子产生而增强。Lyα速度偏移被发现非常大(≳300 km s⁻¹),可能也有助于它们的可探测性。我们发现z≳7星系中的Lyα比具有匹配静止光学谱线性质的较低红移样本弱6-12倍。如果Lyα发射体周围的电离泡相对较小(≲0.5-1 pMpc),我们可以预期在这些电离区域中Lyα会出现如此显著的衰减。我们讨论了可能导致z≳7处Lyα发射较弱的其他几种效应。对Lyα发射体附近较暗星系进行深度光谱观测将更好地刻画该场中电离泡的物理尺度。

英文摘要:

We describe new JWST/NIRSpec observations of galaxies at $z\gtrsim7$ taken from the CEERS survey. Previous observations of this area have revealed associations of Ly$α$ emitters at redshifts ($z=7.5$, $7.7$, $8.7$) where the intergalactic medium (IGM) is thought to be mostly neutral, leading to suggestions that these systems are situated in large ionized bubbles. We identify 21 $z\gtrsim7$ galaxies with robust redshifts in the CEERS dataset, including 10 in the Ly$α$ associations. Their spectra are indicative of very highly ionized and metal poor gas, with line ratios (O32 $=17.84$ and Ne3O2 $=0.89$, linear scale) and metallicity ($12+\log{(\rm{O/H})}=7.84$) that are rarely seen at lower redshifts. We find that the most extreme spectral properties are found in the six $z\gtrsim7$ Ly$α$ emitters in the sample. Each has a hard ionizing spectrum indicating that their visibility is likely enhanced by efficient ionizing photon production. Ly$α$ velocity offsets are found to be very large ($\gtrsim300$ km s$^{-1}$), likely also contributing to their detectability. We find that Ly$α$ in $z\gtrsim7$ galaxies is $6-12\times$ weaker than in lower redshift samples with matched rest-optical spectral properties. If the bubbles around the Ly$α$ emitters are relatively small ($\lesssim0.5-1$ pMpc), we may expect such significant attenuation of Ly$α$ in these ionized regions. We discuss several other effects that may contribute to weaker Ly$α$ emission at $z\gtrsim7$. Deep spectroscopy of fainter galaxies in the vicinity of the Ly$α$ emitters will better characterize the physical scale of the ionized bubbles in this field.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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