Thermal Instability behind a Shock Wave in H I and Molecular Clouds
Thermal Instability behind a Shock Wave in H I and Molecular Clouds
复制标题
H I 和分子云中冲击波背后的热不稳定性
DOI：
10.1088/0004-637x/775/1/26
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Y.
中科院分区：
文献类型：
--
作者：
Aota;T. Inoue;T.;Aikawa;Y.
我们通过详细的冷却、加热和化学过程进行一维流体动力学模拟，以检查冷中性介质 (CNM) 和分子云中冲击气体的热稳定性。我们发现 CNM 和分子云在冲击波后面的冷却层中都可能是热不稳定的。 CNM 中热不稳定性的特征波长范围为 10− 5 pc 至 0.1 pc，分子云中热不稳定性的特征波长范围为 10− 7 pc 至 0.1 pc。这与在 CNM 和分子云中观察到的微小尺度结构的大小相吻合，表明冲击气体中的热不稳定性可能是星际介质中这些微小结构的形成机制。我们还计算了热不稳定性的电子折叠数，以估计冲击气体中密度波动的放大程度。 CNM 中的密度扰动增长了 exp (5)≃ 150 倍，而分子云中的扰动仅在高马赫数激波后增长了几倍。密度较低且速度较高时，放大系数较大。通过冲击气体中的热不稳定性形成非常小尺度的结构在较低密度下更有效。
We performed one-dimensional hydrodynamic simulations with detailed cooling, heating, and chemical processes to examine the thermal stability of shocked gas in cold neutral medium (CNM) and molecular clouds. We find that both CNM and molecular clouds can be thermally unstable in the cooling layer behind the shock wave. The characteristic wavelength of the thermal instability ranges from 10− 5 pc to 0.1 pc in the CNM, and from 10− 7 pc to 0.1 pc in the molecular clouds. This coincides with the size of observed tiny scale structures in the CNM and molecular clouds, indicating that the thermal instability in the shocked gas could be a formation mechanism of these tiny structures in the interstellar medium. We have also calculated the e-folding number of the thermal instability to estimate the amplification of the density fluctuation in the shocked gas. Density perturbations in the CNM grow by a factor of exp (5)≃ 150, whereas the perturbations in the molecular clouds grow only by a factor of a few behind a high Mach number shock. The amplification factor is larger at lower densities and higher velocities. Formation of very small scale structures by thermal instability in shocked gas is more effective in lower densities.