TESTING MAGNETIC STAR FORMATION THEORY
TESTING MAGNETIC STAR FORMATION THEORY
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DOI：
10.1088/0004-637x/692/1/844
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发表时间：
2009-02-10
影响因子：
4.9
通讯作者：
Troland, Thomas H.
中科院分区：
文献类型：
--
作者：
Crutcher, Richard M.;Hakobian, Nicholas;Troland, Thomas H.
塞曼观测分子云产生的视线分量B-LOS的磁矢量B，这使得它有可能测试两个主要的极端情况下的理论驱动星星的形成-双极扩散或湍流。然而，B的三个组成部分中只有一个是可测量的，因此测试是统计的而不是直接的，并且它们不是确定的。我们在这里报告的塞曼效应的观测结果在18厘米线的OH在周围的四个分子云的核心已实现在相同的线路检测B-LOS的包络区域，并评估的质量比磁通量，M/Φ，云的核心和信封之间。这种相对M/Phi测量减少了先前研究中的不确定性，例如B和视线之间的角度以及[OH/H]的值。我们的结果是，对于所有四种云，核心与M/Phi的包络值之比R'小于1。换句话说，核心与总云M/Phi的比率R小于1。核心形成的极端情况或理想化（无湍流）双极扩散理论要求中心M/Phi与总M/Phi的比率近似等于原始亚临界M/Phi的倒数，或R' > 1。我们的四个云R' > 1的概率是3 × 10（-7）;因此，我们的结果与这四个核是由双极扩散形成的假设明显矛盾。高度超Alfvenic湍流模拟产生了较宽范围的相对M/Phi，但有利于比值R < 1，正如我们所观察到的。我们的实验仅限于四个云，我们只能直接测试双极扩散驱动星星形成的极端情况下的“理想化”模型的预测，这些模型具有规则的磁场形态。然而，我们的实验结果与“理想化”的强场双极扩散理论的星星形成是不一致的。比较我们的结果与更现实的模型和模拟，包括双极扩散和湍流可能有助于完善我们的理解磁场和湍流的相对重要性在星星形成过程。
Zeeman observations of molecular clouds yield the line-of-sight component B-LOS of the magnetic vector B, which makes it possible to test the two major extreme-case theories of what drives star formation-ambipolar diffusion or turbulence. However, only one of the three components of B is measurable, so tests have been statistical rather than direct, and they have not been definitive. We report here observations of the Zeeman effect in the 18 cm lines of OH in the envelope regions surrounding four molecular cloud cores toward which detections of B-LOS have been achieved in the same lines, and evaluate the ratio of mass-to-magnetic flux, M/Phi, between the cloud core and envelope. This relative M/Phi measurement reduces uncertainties in previous studies, such as the angle between B and the line of sight and the value of [OH/H]. Our result is that for all four clouds, the ratios R' of the core to the envelope values of M/Phi are less than 1. Stated another way, the ratios R of the core to the total cloud M/Phi are less than 1. The extreme case or idealized (no turbulence) ambipolar diffusion theory of core formation requires the ratio of the central to total M/Phi to be approximately equal to the inverse of the original subcritical M/Phi, or R' > 1. The probability that all four of our clouds have R' > 1 is 3 x 10(-7); our results are therefore significantly in contradiction with the hypothesis that these four cores were formed by ambipolar diffusion. Highly super-Alfvenic turbulent simulations yield a wide range of relative M/Phi, but favor a ratio R < 1, as we observe. Our experiment is limited to four clouds, and we can only directly test the predictions of the extreme-case " idealized" models of ambipolar-diffusion driven star formation, which have a regular magnetic field morphology. Nonetheless, our experimental results are not consistent with the " idealized" strong field, ambipolar diffusion theory of star formation. Comparisons of our results with more realistic models and simulations that include both ambipolar diffusion and turbulence may help to refine our understanding of the relative importance of magnetic fields and turbulence in the star formation process.