Electron Densities and Nitrogen Abundances in Ionized Gas Derived Using [N ii] Fine-structure and Hydrogen Recombination Lines
Electron Densities and Nitrogen Abundances in Ionized Gas Derived Using [N ii] Fine-structure and Hydrogen Recombination Lines
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DOI：
10.3847/1538-4357/ab46c2
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发表时间：
2019-05
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影响因子：
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通讯作者：
J. Pineda;S. Horiuchi;L. Anderson;M. Luisi;W. Langer;P. Goldsmith;T. Kuiper;G. Bryden;Melissa Soriano;T. Joseph W. Lazio
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作者：
J. Pineda;S. Horiuchi;L. Anderson;M. Luisi;W. Langer;P. Goldsmith;T. Kuiper;G. Bryden;Melissa Soriano;T. Joseph W. Lazio
本文提出了一种利用[N_（ii）] 205 μm谱线强度与氢射电复合谱线强度之比来推算电离气体电子密度的方法。我们使用这种方法来获得电子密度的21个速度分量在11条视线通过银河系，包括银河系中心。我们用Herschel/HIFI和索菲亚/GREAT仪器在高光谱分辨率下观测了[N ii] 205 μm，用绿色银行望远镜和NASA深空网络深空站43（DSS-43）望远镜观测了RRL。我们发现典型的电子密度在8到170 cm−3之间，这与在低光谱分辨率下使用[N ii] 205 μm/122 μm比率与Herschel/PACS在银河平面上的较大样本视线上得出的结果一致。通过匹配由[N ii] 205 μm/RRL强度比和[N ii] 122 μm/205 μm强度比导出的电子密度，我们导出了大多数速度分量的氮分数丰度。我们研究了内星系（Rgal < 6 kpc）的N/H比对银河系中心距离的依赖关系，这是光学研究中由于尘埃消光而无法实现的。我们发现，根据我们的数据得出的银河系内部氮丰度分布的斜率与光学研究中在银河系外部发现的一致。这一结果与银河系内部氮丰度分布较平坦的一些建议不一致。
We present a method for deriving the electron density of ionized gas using the ratio of the intensity of the [N ii] 205 μm line to that of hydrogen radio recombination lines (RRLs). We use this method to derive electron densities of 21 velocity components in 11 lines of sight through the Galaxy, including the Galactic center. We observed, at high spectral resolution, the [N ii] 205 μm with the Herschel/HIFI and SOFIA/GREAT instruments and the RRLs with the Green Bank Telescope and the NASA Deep Space Network Deep Space Station 43 (DSS-43) telescope. We find typical electron densities between 8 and 170 cm−3, which are consistent with those derived at low spectral resolution using the [N ii] 205 μm/122 μm ratio with Herschel/PACS on a larger sample of sight lines in the Galactic plane. By matching the electron densities derived from the [N ii] 205 μm/RRL intensity ratio and the [N ii] 122 μm/205 μm intensity ratio, we derive the nitrogen fractional abundance for most of the velocity components. We investigate the dependence of the N/H ratio on galactocentric distance in the inner Galaxy (Rgal < 6 kpc), which is inaccessible in optical studies owing to dust extinction. We find that the distribution of nitrogen abundances in the inner Galaxy derived from our data has a slope that is consistent with that found in the outer Galaxy in optical studies. This result is inconsistent with some suggestions of a flatter distribution of the nitrogen abundance in the inner Galaxy.