ISM中规则磁场和随机磁场的研究：极化矢量统计和F-F技术
Studies of regular and random magnetic fields in the ISM: statistics of polarization vectors and the Chandrasekhar-Fermi technique
摘要：
偏振测量是一种广泛应用于跟踪星际磁场在天空平面上投影的工具。此外，还可以基于Escherasekhar-Fermi方法从极化图估计磁场强度。在这项工作中，我们提出的结果湍流，等温，3-D模拟的亚/超音速和亚/超Alfvenic的情况下。与立方体，假设完美的晶粒对齐，我们创建了合成极化地图的平均磁场相对于视线（LOS）的不同方向。我们表明，偏振角的色散依赖于平均磁场的角度，关于LOS和阿尔芬马赫数。然而，偏振角的二阶结构函数遵循关系式$SF \propto l^α$，其中$α$仅取决于Alfvenic马赫数。结果表明，偏振度与柱密度之间存在反相关关系，其指数为$γ\sim -0.5$，与观测结果一致，这可以用偏振角沿LOS方向在密集区域内的色散增加来解释。然而，这种效应只在超音速，但亚Alfvenic，模拟中观察到。对于超阿尔文模型和亚音速模型，极化度与柱密度有关。我们的主要定量结果是CF方法的广义方程，这使我们能够确定磁场强度的极化图与错误$< 20%$。我们还占CF方法的观测分辨率的作用。
英文摘要：
Polarimetry is extensively used as a tool to trace the interstellar magnetic field projected on the plane of sky. Moreover, it is also possible to estimate the magnetic field intensity from polarimetric maps based on the Chandrasekhar-Fermi method. In this work, we present results for turbulent, isothermal, 3-D simulations of sub/supersonic and sub/super-Alfvenic cases. With the cubes, assuming perfect grain alignment, we created synthetic polarimetric maps for different orientations of the mean magnetic field with respect to the line of sight (LOS). We show that the dispersion of the polarization angle depends on the angle of the mean magnetic field regarding the LOS and on the Alfvenic Mach number. However, the second order structure function of the polarization angle follows the relation $SF \propto l^α$, $α$ being dependent exclusively on the Alfvenic Mach number. The results show an anti-correlation between the polarization degree and the column density, with exponent $γ\sim -0.5$, in agreement with observations, which is explained by the increase in the dispersion of the polarization angle along the LOS within denser regions. However, this effect was observed exclusively on supersonic, but sub-Alfvenic, simulations. For the super-Alfvenic, and the subsonic model, the polarization degree showed to be intependent on the column density. Our major quantitative result is a generalized equation for the CF method, which allowed us to determine the magnetic field strength from the polarization maps with errors $< 20%$. We also account for the role of observational resolution on the CF method.
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