星系中扩散气体的电离：热的低质量演化恒星的工作-会议录IAUS284
Ionization of the diffuse gas in galaxies: Hot low-mass evolved stars at work -- proceedings IAUS284
摘要：
通过对NGC 891的研究，我们重新讨论了晚型星系中弥散介质的电离问题。到目前为止所考虑的模型最重要的挑战是观察到的[OIII]/Hb，[OII]/Hb和[NII]/Ha随着到银道面距离的增加而增加。我们提出了一个方案的基础上，在这个星系中的大质量OB星和热的低质量演化恒星（HOLMES）的预期人口来解释这一观测事实。在这种情况下，我们构建了一个细网格的光电离模型的框架。对于银河纬度z的每个值，我们寻找同时适合[OIII]/Hb，[OII]/Hb和[NII]/Ha比值的观测值的模型。对于z的每一个值，我们找到一系列的解决方案，这取决于氧丰度的值。拟合观测结果的模型表明，随着z的增加，电子密度有系统地降低。只有当限制到太阳氧丰度模型时，它们才随着z的增加而被HOLMES所主导，这表明银道面上方的金属丰度应该接近太阳。它们还表明N/O随着z的增加而增加。
英文摘要：
We revisit the question of the ionization of the diffuse medium in late type galaxies, by studying NGC 891. The most important challenge for the models considered so far was the observed increase of [OIII]/Hb, [OII]/Hb, and [NII]/Ha with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic latitude z we look for the models which simultaneously fit the observed values of the [OIII]/Hb, [OII]/Hb, and [NII]/Ha ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.
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