超音速薄壳与分子云的相互作用
On the interaction of a thin, supersonic shell with a molecular cloud
摘要：
分子云是恒星的摇篮，然而，分子云中恒星的形成取决于周围的物理条件。在自由落体时间内，MCs暴露于许多动力学现象，其中，与薄而致密的气体壳层的相互作用只是其中之一。下面，我们提出的结果，从自引力，3-D平滑粒子流体动力学（{ \small SPH}）模拟的问题，七个实现的问题已经通过改变碰撞前的云内的密度，碰撞后的冲击的性质，在计算域中的空间分辨率。不管激波的类型如何，激波云中很容易出现一个由密集细丝组成的复杂网络，这些细丝被数值噪声所播种。致密和稀薄气体相的分离也表现为气体密度的双峰分布。我们证明，稀薄气体的功率谱是Kolomogorov一样，而密度较大的气体是相当陡峭的。作为主要问题的必然结果，我们还研究了{ \small SPH}人工粘性对入射壳层影响的可能退化效应。据观察，更强的粘度导致更大的冲击后耗散，强烈减速的入射冲击波阵面和促进连续结构的形成，虽然在一个更长的时间尺度。我们的结论是，太大的粘度可能会增加倾向于引力约束的结构，导致非物理的碎裂。另一方面，分辨率不足，似乎抑制碎裂。在两个极端情况下测试结果的收敛性，首先使用超过一百万个粒子重复测试用例，然后使用原始测试用例中的一半粒子数重复测试用例。
英文摘要：
Molecular clouds (MCs) are stellar nurseries, however, formation of stars within MCs depends on the ambient physical conditions. MCs, over a free-fall time are exposed to numerous dynamical phenomena, of which, the interaction with a thin, dense shell of gas is but one. Below we present results from self-gravitating, 3-D smoothed particle hydrodynamics ({\small SPH}) simulations of the problem; seven realisations of the problem have been performed by varying the precollision density within the cloud, the nature of the post-collision shock, and the spatial resolution in the computational domain. Irrespective of the type of shock, a complex network of dense filaments, seeded by numerical noise, readily appears in the shocked cloud. Segregation of the dense and rarefied gas phases also manifests itself in a bimodal distribution of gas density. We demonstrate that the power-spectrum for rarefied gas is Kolomogorov like, while that for the denser gas is considerably steeper. As a corollary to the main problem, we also look into the possibly degenerative effect of the {\small SPH} artificial viscosity on the impact of the incident shell. It is observed that stronger viscosity leads to greater post-shock dissipation, that strongly decelerates the incident shock-front and promotes formation of contiguous structure, albeit on a much longer timescale. We conclude that too much viscosity is likely to enhance the proclivity towards gravitational boundedness of structure, leading to unphysical fragmentation.On the other hand, insufficient resolution appears to suppress fragmentation. Convergence of results is tested at both extremes, first by repeating the test case with more than a million particles and then with only half the number of particles in the original test case.
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