On the structure of the turbulent interstellar atomic hydrogen. I- Physical characteristics Influence and nature of turbulence in a thermally bistable flow
On the structure of the turbulent interstellar atomic hydrogen. I- Physical characteristics Influence and nature of turbulence in a thermally bistable flow
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关于湍流星际原子氢的结构。
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
E. Audit
中科院分区：
文献类型：
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作者：
P. Hennebelle;E. Audit
目标。本文详细研究了湍流两相星际原子气体的统计性质。方法.我们提出了高分辨率的二维数值模拟的星际原子氢，它描述了它在3至4个数量级的空间尺度。结果模拟产生具有大或小柱密度的自然小尺度结构。很容易提出，前者与ISM中观察到的微小尺度结构有关。我们计算了CNM结构的质谱，发现N（M）dM / M为1.7 dM，这与CO团簇的质谱非常相似。我们提出了一个理论解释的基础上的形式主义的启发，从新闻和Schecter（1974年）的方法，并使用的事实，在WNM内的湍流是亚音速。该理论预测2D中N（M）/ M为5/3，3D中N（M）/ M为16/9。我们计算的速度和密度功率谱，并得出结论，虽然后者是相当平坦的，如在超音速等温模拟中观察到的，前者遵循柯尔莫哥洛夫预测，并占主导地位的螺线管组件。这是由于即使当均方根马赫数（WNM的）不大时，流动也会产生大的密度波动。我们还发现，而在大尺度上的能量主要是在WNM，在较小的尺度上，它是由CNM碎片的动能为主。结论.我们发现，湍流的热膨胀流一样，星际氢原子，是在某种程度上不同于湍流的超音速等温气体。在配套文件中，我们比较了数值结果与原子氢观测，并表明模拟很好地再现各种观测功能。
Aims. We study in some details the statistical properties of the turbulent 2-phase interstellar atomic gas. Methods. We present high resolution bidimensional numerical simulations of the interstellar atomic hydrogen which describe it over 3 to 4 orders of magnitude in spatial scales. Results. The simulations produce naturally small scale structures having either large or small column density. It is tempting to propose that the former are connected to the tiny small scale structures observed in the ISM. We compute the mass spectrum of CNM structures and find that N(M)dM / M 1.7 dM, which is remarkably similar to the mass spectrum inferred for the CO clumps. We propose a theoretical explanation based on a formalism inspired from the Press & Schecter (1974) approach and used the fact that the turbulence within WNM is subsonic. This theory predicts N(M) / M 5/3 in 2D and N(M) / M 16/9 in 3D. We compute the velocity and the density power-spectra and conclude that, although the latter is rather flat, as observed in supersonic isothermal simulations, the former follows the Kolmogorov prediction and is dominated by its solenoidal component. This is due to the bistable nature of the flow which produces large density fluctuations even when the rms Mach number (of WNM) is not large. We also find that, whereas the energy at large scales is mainly in the WNM, at smaller scales, it is dominated by the kinetic energy of the CNM fragments. Conclusions. We find that turbulence in a thermally bistable flow like the atomic interstellar hydrogen, is somehow different from turbulence in a supersonic isothermal gas. In a companion paper, we compare the numerical results with atomic hydrogen observations and show that the simulations well reproduce various observational features.