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arXiv 1701.07129astro-ph.GA
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磁场作用下星际非均匀湍流HI气体21 cm HI谱线合成观测

Synthetic Observations of 21cm HI Line Profiles from Inhomogeneous Turbulent Interstellar HI Gas with Magnetic Field

Yasuo Fukui, Takahiro Hayakawa, Tsuyoshi Inoue, Kazufumi Torii, Ryuji Okamoto, Kengo Tachihara, Toshikazu Onishi, Katsuhiro Hayashi

摘要:

我们利用Inoue和Inutsuka(2012)对非均匀湍流星际介质(ISM)的磁流体动力学数值模拟,在21 cm波长处对星际原子氢进行了合成观测。冷中性介质(CNM)表现出明显的团块状分布,其体积填充因子较小,为3.5%;而暖中性介质(WNM)表现出明显不同的光滑分布,其体积填充因子较大,为96.5%。在天空投影中,CNM呈现出亚pc宽度的高度连续分布,而WNM呈现出平滑的扩展分布。在HI光学深度中,CNM占主导地位,WNM的贡献小得可以忽略。CNM的投影面积覆盖率为30%,而WNM的覆盖率为70%。这导致对射电连续致密源的发射-吸收测量倾向于以70%的概率对WNM进行采样,从而产生比块状HI气体更小的HI光学深度和更小的HI柱密度。的发射-吸收测量,这是显着的小规模的大波动的CNM属性的影响,是不适合的散装HI气体的特征。更大的光束发射测量,能够充分采样的HI气体将提供一个更好的工具,用于此目的,如果一个可靠的代理氢柱密度,可能的灰尘光学厚度和伽马射线,是可用的。

英文摘要:

We carried out synthetic observations of interstellar atomic hydrogen at 21cm wavelength by utilizing the magneto-hydrodynamical numerical simulations of the inhomogeneous turbulent interstellar medium (ISM) Inoue and Inutsuka (2012). The cold neutral medium (CNM) shows significantly clumpy distribution with a small volume filling factor of 3.5%, whereas the warm neutral medium (WNM) distinctly different smooth distribution with a large filling factor of 96.5%. In projection on the sky, the CNM exhibits highly filamentary distribution with a sub-pc width, whereas the WNM shows smooth extended distribution. In the HI optical depth the CNM is dominant and the contribution of the WNM is negligibly small. The CNM has an area covering factor of 30% in projection, while the WNM has a covering factor of 70%. This causes that the emission-absorption measurements toward radio continuum compact sources tend to sample the WNM with a probability of 70%, yielding smaller HI optical depth and smaller HI column density than those of the bulk HI gas. The emission-absorption measurements, which are significantly affected by the small-scale large fluctuations of the CNM properties, are not suitable to characterize the bulk HI gas. Larger-beam emission measurements which are able to fully sample the HI gas will provide a better tool for that purpose, if a reliable proxy for hydrogen column density, possibly dust optical depth and gamma rays, is available.

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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