THE TWO STATES OF STAR-FORMING CLOUDS
THE TWO STATES OF STAR-FORMING CLOUDS
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恒星形成云的两种状态
DOI：
10.1088/0004-637x/750/1/13
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
M. Norman
中科院分区：
文献类型：
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作者：
D. Collins;A. Kritsuk;P. Padoan;Hui Li;Haoting Xu;S. Ustyugov;M. Norman
通过高分辨率模拟和自适应网格细化，研究了自重力和磁场对等温分子云中超音速湍流的影响。这些模拟使用大的根网格（5123）来捕捉湍流，并使用四个级别的细化来跟随崩溃到高密度，有效分辨率为81923。进行了三次马赫数9的模拟，两次是超级阿尔夫曼和一次是跨阿尔夫曼。我们发现重力将云分成两个种群，一个低密度的湍流状态和一个高密度的坍缩状态。研究了不同磁场强度对统计性质的影响：密度概率分布函数近似对数正态分布，速度功率谱斜率随平均磁场强度的减小而减小，速度与磁场的对准度随磁场的增大而增大，磁场概率分布可以拟合为拉伸指数。密度概率分布服从幂律，坍缩率随平均场的增大而减小，密度功率谱斜率为正，P(ρ, k)∝k，热磁压比在所有平均场强下大致为1，动磁压比在所有平均场强下大于1，磁场分布服从幂律分布。塌缩区域的高阿尔夫萨芬马赫数解释了最近观测到的磁影响随密度减小的现象。我们还发现高密度状态通常存在于由汇聚流形成的细丝中，这与赫歇尔最近的观察结果一致。对现有恒星形成理论的可能修正进行了探讨。讨论了形成恒星的云的整体反阿尔夫萨奇性质。
We examine the effects of self-gravity and magnetic fields on supersonic turbulence in isothermal molecular clouds with high-resolution simulations and adaptive mesh refinement. These simulations use large root grids (5123) to capture turbulence and four levels of refinement to follow the collapse to high densities, for an effective resolution of 81923. Three Mach 9 simulations are performed, two super-Alfvénic and one trans-Alfvénic. We find that gravity splits the clouds into two populations, one low-density turbulent state and one high-density collapsing state. The low-density state exhibits properties similar to non-self-gravitating in this regime, and we examine the effects of varied magnetic field strength on statistical properties: the density probability distribution function is approximately lognormal, the velocity power spectral slopes decrease with decreasing mean field strength, the alignment between velocity and magnetic field increases with the field, and the magnetic field probability distribution can be fitted to a stretched exponential. The high-density state is well characterized by self-similar spheres: the density probability distribution is a power law, collapse rate decreases with increasing mean field, density power spectra have positive slopes, P(ρ, k)∝k, thermal-to-magnetic pressure ratios are roughly unity for all mean field strengths, dynamic-to-magnetic pressure ratios are larger than unity for all mean field strengths, the magnetic field distribution follows a power-law distribution. The high Alfvén Mach numbers in collapsing regions explain the recent observations of magnetic influence decreasing with density. We also find that the high-density state is typically found in filaments formed by converging flows, consistent with recent Herschel observations. Possible modifications to existing star formation theories are explored. The overall trans-Alfvénic nature of star-forming clouds is discussed.
自重力气体 (M)HD 模拟的新 Jean 分辨率准则：在重力驱动湍流磁场放大中的应用
DOI：
10.1088/0004-637x/731/1/62
发表时间：
2011
期刊：
The Astrophysical Journal
影响因子：
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作者：
Christoph Federrath;Sharanya Sur;Dominik R. G Schleicher;Robi Banerjee;Ralf S. Klessen
通讯作者：
Ralf S. Klessen