量化从大尺度云到坍缩核的磁场的意义：自相似性、质量通量比和恒星形成效率
Quantifying the Significance of the Magnetic Field from Large-Scale Cloud to Collapsing Core: Self-Similarity, Mass-to-Flux Ratio and Star Formation Efficiency
摘要：
分析了从最大母云（$\sim$ 2~pc，JCMT）到大尺度包层（$\sim$ 0.5~pc，BIMA）再到坍缩核e2（$\sim$ 60~mpc，SMA）的大质量恒星形成区W51的尘埃偏振观测结果。磁场和尘埃发射梯度方向揭示了一种相关性，这种相关性随着分辨率的提高而变得越来越紧密。应用先前开发的极化强度梯度方法（Koch等人，2012），以量化磁场的显著性。该技术提供了一种方法来估计与重力相比的局部磁场力，而不需要任何质量或场强测量，仅利用反映各种力的几何印记的测量角度。所有三个数据集都清楚地显示了磁场与重力之比具有不同特征的区域。这个力比的方位平均径向分布揭示了从较大距离处的场优势到更靠近发射峰的重力优势的过渡。将这些配置文件规范化为特征核心尺度指向自相似性。此外，极化强度梯度法与质量通量比相联系，提供了一种新的方法来估计后者没有质量和场强输入。从磁超临界到亚临界状态的过渡作为距离的函数的发射峰被发现为e2核心。最后，基于测量的半径依赖的场重力比，我们推导出一个修改后的恒星形成效率与稀释的重力。与标准（自由落体）效率相比，观测场能够将效率降低至10%或更低。
英文摘要：
Dust polarization observational results are analyzed for the high-mass star formation region W51 from the largest parent cloud ($\sim$ 2~pc, JCMT) to the large-scale envelope ($\sim$ 0.5~pc, BIMA) down to the collapsing core e2 ($\sim$ 60~mpc, SMA). Magnetic field and dust emission gradient orientations reveal a correlation which becomes increasingly more tight with higher resolution. The previously developed polarization - intensity gradient method (Koch et al. 2012) is applied in order to quantify the magnetic field significance. This technique provides a way to estimate the local magnetic field force compared to gravity without the need of any mass or field strength measurements, solely making use of measured angles which reflect the geometrical imprint of the various forces. All three data sets clearly show regions with distinct features in the field-to-gravity force ratio. Azimuthally averaged radial profiles of this force ratio reveal a transition from a field dominance at larger distances to a gravity dominance closer to the emission peaks. Normalizing these profiles to a characteristic core scale points toward self-similarity. Furthermore, the polarization intensity-gradient method is linked to the mass-to-flux ratio, providing a new approach to estimate the latter one without mass and field strength inputs. A transition from a magnetically supercritical to a subcritical state as a function of distance from the emission peak is found for the e2 core. Finally, based on the measured radius-dependent field-to-gravity force ratio we derive a modified star formation efficiency with a diluted gravity force. Compared to a standard (free-fall) efficiency, the observed field is capable of reducing the efficiency down to 10\% or less.
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