MOSDEF巡天：氖作为ISM高红移物理条件的探针
The MOSDEF Survey: Neon as a Probe of ISM Physical Conditions at High Redshift
摘要：
我们提出的结果氖发射的$z\sim2$恒星形成星系的MOSFIRE深演化场（MOSDEF）调查。在61个星系中的$\geq3σ$处探测到双电离氖（[NeIII]3869），相当于在类似红移处探测到的H $α$、H $β$和[OIII] $5007$的MOSDEF样本的$\sim$的25%。我们认为，氖发射线的属性与[NeIII]3869检测和复合$z\sim2$光谱的恒星质量的两个单独的星系。由于不需要[NeIII]3869检测，后者提供了MOSDEF样品中氖发射线特性的更具代表性的图片。正如基于质量-金属丰度关系所预期的那样，[NeIII]3869/[OII]3727比率（Ne 3 O2）与$z\sim2$星系中的恒星质量反相关。它还与[OIII] $5007$ /[OII] $3727$比值（O ~（32））呈正相关，但与本星系和单个H~II区相比，在O ~（32）固定时，$z\sim2$线比值向高Ne ~ 3 O ~ 2方向偏移。尽管在$z\sim2$的固定O32下向较高的Ne 3 O2偏移，但推断的基于Ne 3 O2的金属丰度的偏差很小。因此，Ne 3 O2可以作为一个重要的金属丰度指标深入到再电离时代。通过分析其他的静止-光学谱线比，包括[NeIII] $3869$ /[OIII] $5007$（Ne 3 O3）和[OIII] $5007$ /H $β$（O3 H $β$），我们得出结论：$z\sim2$恒星形成星系的星云发射谱线比表明了一个较硬的电离光谱（较低的恒星金属丰度，即，Fe/H）在固定的气相氧丰度，相比系统在$z\sim0$。这些基于氖的新结果支持了由氧、氮、氢和硫发射描绘的物理图像，即在化学上年轻的、$α$增强的大质量恒星照射的高红移恒星形成星系中的电离ISM。
英文摘要：
We present results on the properties of neon emission in $z\sim2$ star-forming galaxies drawn from the MOSFIRE Deep Evolution Field (MOSDEF) survey. Doubly-ionized neon ([NeIII]3869) is detected at $\geq3σ$ in 61 galaxies, representing $\sim$25% of the MOSDEF sample with H$α$, H$β$, and [OIII]$5007$ detections at similar redshifts. We consider the neon emission-line properties of both individual galaxies with [NeIII]3869 detections and composite $z\sim2$ spectra binned by stellar mass. With no requirement of [NeIII]3869 detection, the latter provide a more representative picture of neon emission-line properties in the MOSDEF sample. The [NeIII]3869/[OII]3727 ratio (Ne3O2) is anti-correlated with stellar mass in $z\sim2$ galaxies, as expected based on the mass-metallicity relation. It is also positively correlated with the [OIII]$5007$/[OII]$3727$ ratio (O32), but $z\sim2$ line ratios are offset towards higher Ne3O2 at fixed O32, compared with both local star-forming galaxies and individual H~II regions. Despite the offset towards higher Ne3O2 at fixed O32 at $z\sim2$, biases in inferred Ne3O2-based metallicity are small. Accordingly, Ne3O2 may serve as an important metallicity indicator deep into the reionization epoch. Analyzing additional rest-optical line ratios including [NeIII]$3869$/[OIII]$5007$ (Ne3O3) and [OIII]$5007$/H$β$ (O3H$β$), we conclude that the nebular emission-line ratios of $z\sim2$ star-forming galaxies suggest a harder ionizing spectrum (lower stellar metallicity, i.e., Fe/H) at fixed gas-phase oxygen abundance, compared to systems at $z\sim0$. These new results based on neon lend support to the physical picture painted by oxygen, nitrogen, hydrogen, and sulfur emission, of an ionized ISM in high-redshift star-forming galaxies irradiated by chemically young, $α$-enhanced massive stars.
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