The Warm Ionized Medium in the Milky Way and Other Galaxies
The Warm Ionized Medium in the Milky Way and Other Galaxies
复制标题
银河系和其他星系中的温暖电离介质
DOI：
10.1086/317210
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
J. Mathis
中科院分区：
文献类型：
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作者：
J. Mathis
现在已经观测到来自本地星际介质的“热电离介质”（WIM，或等价的“扩散电离气体”）、来自银河系英仙座臂以及其他几个星系的几条发射线。这些观测的有趣特征包括[N II] λ6563（在某些情况下为~Hα）的强大强度，以及[S II] λ6717/[N II] λ6583在所有位置和物体上几乎相同（~0.6-0.7）。其他谱线比率（例如，[O III] λ5007/Hβ）变化很大。本文提出了简单的光电离模型，再现了观测到的光谱，提供额外的加热，超出了光电离所提供的假设。同样的额外加热被用于所有恒星温度组合在一起的模型，尽管它很容易依赖于T*。与观测到的气相丰度（非太阳能）相比，在b = 0°时，不需要额外加热，S/H = 13 ppm，而不是太阳能（~20 ppm）。在b = -35°观测到的局部气体需要额外加热约Γ-25 = 0.75，其中Γ-25是额外加热，单位为10-25 ergs -1 H-1 s-1。在英仙座臂上也有类似的结果：在|z| = 500pc时需要很少的额外加热，而在|z| = 1.2 kpc时需要Γ-25 = 3.0。为了符合观测结果，英仙座臂中的气相组成必须根据观测到的银河系丰度梯度的要求减少。NGC 891（其他观测最好的星系）在|z| = 1 kpc和2 kpc的要求与英仙座臂相似：在平面附近很少或没有额外的加热（在这种情况下为1 kpc）和Γ-25 ~ 3在|z| = 2 kpc。在NGC 891中，λ5007/Hα也随着|z|的增加而增加，这只有在大部分电离辐射由非常热的恒星（O4型：T* ~ 50,000 K）提供的情况下才能实现。要么它们的辐射必须通过很少的干涉物质从平面传播到高|z|，要么恒星位于高|z|。额外加热的总功率要求是在不额外加热的情况下使WIM光解离的功率的15%。额外加热使[O II] λ3727/Hβ增强。图1显示预测值之间存在差异，但该比率可以作为额外加热的有用诊断。[S III] λλ9065, 9531线（见图2）在诊断额外加热时不起作用。
There are now observations of several emission lines from the "warm ionized medium" (WIM or, equivalently, the "diffuse ionized gas") of the local interstellar medium, from the Perseus arm in the Milky Way, and also in several other galaxies. Interesting features of these observations include the great strength of [N II] λ6563 (~Hα in some cases) and the fact that [S II] λ6717/[N II] λ6583 is almost the same (~0.6-0.7) in all locations and objects. Other line ratios (e.g., [O III] λ5007/Hβ) vary considerably. This paper presents simple photoionization models that reproduce the observed spectra, providing extra heating beyond that supplied by photoionization is assumed. The same extra heating was used for models of all stellar temperatures being combined together, although it could easily depend on T*. With observed gas-phase abundances (not solar), the line ratios in the Local arm at b = 0° are fitted with no extra heating and S/H = 13 ppm, as opposed to solar (~20 ppm). Local gas observed at b = -35° requires extra heating of about Γ-25 = 0.75, where Γ-25 is the extra heating in units of 10-25 ergs H-1 s-1. In the Perseus arm there are similar results: little extra heating is required at |z| = 500 pc, and Γ-25 = 3.0 is needed at |z| = 1.2 kpc. To fit the observations, the gas-phase composition in the Perseus arm must be reduced as required by the Galactic abundance gradient observed for H II regions. The requirements for NGC 891 (the best observed other galaxy) at |z| = 1 kpc and 2 kpc are similar to the Perseus arm: little or no extra heating near the plane (1 kpc in this case) and Γ-25 ~ 3 at |z| = 2 kpc. In NGC 891 there is also an increase of λ5007/Hα with |z| that can only come about if most of the ionizing radiation is supplied by very hot stars (type O4: T* ~ 50,000 K). Either their radiation must propagate from the plane to high |z| through very little intervening matter, or else the stars are located at high |z|. The total power requirement of the extra heating is ≲15% of the power to photoionize the WIM without extra heating. Extra heating enhances [O II] λ3727/Hβ. Figure 1 shows that there is a spread in the predicted values, but the ratio can serve as a useful diagnostic of extra heating. The [S III] λλ9065, 9531 lines (see Fig. 2) are not useful in diagnosing extra heating.