An Origin of Filamentary Structure in Molecular Clouds
An Origin of Filamentary Structure in Molecular Clouds
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DOI：
10.1086/306249
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发表时间：
1998-10
期刊：
影响因子：
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通讯作者：
Tomoya Nagai;S. Inutsuka;S. Miyama
中科院分区：
文献类型：
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作者：
Tomoya Nagai;S. Inutsuka;S. Miyama
本文研究了在线性区域内具有均匀磁场的压力约束等温气体层的引力不稳定性。我们求解了线性扰动增长率的特征值问题，得到了色散关系和特征函数。并与磁化不可压缩层的结果进行了比较。未扰动状态是等温平衡层。未扰动的磁场线平行于层的中平面。对于厚度远大于压力标度高度H的层，平行于磁场的扰动比垂直于磁场的扰动增长得更快。因此，该层分裂成细丝，并且每个细丝的纵轴方向垂直于磁场线。另一方面，厚度远小于H的层对于垂直于磁场的扰动变得更不稳定。在这种情况下，它分裂成细丝，并且每个细丝的纵轴方向平行于磁场线。我们发现，无论磁场强度如何，最不稳定模发生性质变化的临界半厚度为H/（2）1/2。因此，等温层被大于中心压力0.63倍的外部压力所限制，分裂成由平行于它们的磁场穿过的非线性气体云。
The gravitational instability of a pressure-confined isothermal gas layer with uniform magnetic fields is investigated in the linear regime. We solve the eigenvalue problem for the growth rate of linear perturbations and obtain the dispersion relation and eigenfunctions. The result is compared with those of a magnetized incompressible layer. The unperturbed state is an isothermal equilibrium layer. The unperturbed magnetic field lines are parallel to the midplane of the layer. For the layer with a thickness much larger than pressure scale height H, perturbations parallel to the magnetic fields grow faster than those perpendicular to the fields. Therefore the layer fragments into filaments, and the direction of longitudinal axis of each filament is perpendicular to the magnetic field lines. On the other hand, the layer with a thickness much smaller than H becomes more unstable for perturbations perpendicular to the magnetic fields. In this case it fragments into filaments, and the direction of longitudinal axis of each filament is parallel to the magnetic field lines. We find that the critical half-thickness of the layer at which the most unstable mode changes its character is H/(2)1/2 regardless of the strength of magnetic fields. Hence the isothermal layer, which is confined by the external pressure that is larger than about 0.63 times the central pressure, fragments into filamentary gas clouds threaded by magnetic fields parallel to them.