标题： 湍流作为星际介质中的组织者 显示英文标题

标题： Turbulence as an Organizing Agent in the ISM

摘要： 我们讨论HD和MHD可压缩湍流作为星际介质中云形成和云结构形成的机制。 在大尺度星际介质的数值模型结果表明，介质的类似相的外观、云间介质中的典型密度和磁场强度，以及云中的速度弥散-尺寸标度关系可能被理解为星际湍流的结果。 然而，密度-尺寸关系似乎仅适用于最致密的云，这表明最难观测的低柱密度云是湍流瞬态。 然后，我们探讨了适用于分子云尺度的一维和多维高度可压缩多变湍流的一些特性。 在多变指数$\gamma$的低值情况下，湍流可能引发原本线性稳定的云的重力坍缩，除非它们是磁亚临界的。 在高马赫数极限下，密度涨落的性质取决于$\gamma$，并且在任何情况下都不像由伯格斯湍流产生的那样。 在等温（$\gamma=1$）情况下，$\ln (\rho)$的弥散与湍流马赫数成比例。 后一种情况具有对数正态密度概率分布函数，而在高（或低）密度下，$\gamma <1$（或$\gamma >1$）会出现幂律尾部。 显示英文摘要

摘要： We discuss HD and MHD compressible turbulence as a cloud-forming and cloud-structuring mechanism in the ISM. Results from a numerical model of the turbulent ISM at large scales suggest that the phase-like appearance of the medium, the typical values of the densities and magnetic field strengths in the intercloud medium, as well as the velocity dispersion-size scaling relation in clouds may be understood as consequences of the interstellar turbulence. However, the density-size relation appears to only hold for the densest clouds, suggesting that low-column density clouds, which are hardest to observe, are turbulent transients. We then explore some properties of highly compressible polytropic turbulence, in one and several dimensions, applicable to molecular cloud scales. At low values of the polytropic index $\gamma$, turbulence may induce the gravitational collapse of otherwise linearly stable clouds, except if they are magnetically subcritical. The nature of the density fluctuations in the high Mach-number limit depends on $\gamma$, and in no case resembles that resulting from Burgers turbulence. In the isothermal ($\gamma=1$) case, the dispersion of $\ln (\rho)$ scales like the turbulent Mach number. The latter case is singular with a lognormal density pdf, while power-law tails develop at high (resp. low) densities for $\gamma <1$ (resp. $\gamma >1$).