Magnetic fields in molecular clouds: Limitations of the analysis of Zeeman observations
Magnetic fields in molecular clouds: Limitations of the analysis of Zeeman observations
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分子云中的磁场：塞曼观测分析的局限性
DOI：
10.1051/0004-6361/201629001
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发表时间：
2017
影响因子：
6.5
通讯作者：
F. Ober
中科院分区：
文献类型：
--
作者：
R. Brauer;S. Wolf;S. Reissl;F. Ober
塞曼分裂谱线的观测是推导分子云中磁场结构和强度的重要途径。与谱线观测本身的不确定性相反，从这些观测中获得磁场强度的分析方法的不确定性迄今为止还没有得到很好的characteristic.AimsWe调查的分析方法，这是用来从塞曼分裂谱线获得视线（LOS）磁场强度的不确定性的几个物理量的影响。这些数量的密度，温度，速度，和磁场strength.MethodsWe模拟塞曼分裂的1665 MHz OH线与三维辐射传输（RT）扩展ZRAD。这种扩展是基于线RT代码Mol 3D，并已开发的POLArized Radiation Simulator POLARIS.ResultsObservations的OH塞曼效应在典型的分子云不显着影响的分析方法的不确定性。然而，一些观测获得的磁场强度超过~300μG，这可能导致分析方法的不确定性> 10%。我们推导出一个近似值来量化分析方法足够精确的参数范围，并提供将我们的结果转换为其他光谱线和物种的因素。我们将这些转换因子应用于CN，发现在典型的分子云中CN塞曼效应的观测结果并不受分析方法的不确定性的显著影响。此外，我们发现密度对分析方法的不确定性几乎没有影响，除非它达到比分子云中通常发现的值（nH 107 cm-3）更高的值。此外，如果气体速度和磁场都显示出沿着LOS的显著变化，则分析方法的不确定性增加。然而，这种增加应该是小的塞曼观测大多数分子云考虑典型的速度为1公里秒-1。
ContextObservations of Zeeman split spectral lines represent an important approach to derive the structure and strength of magnetic fields in molecular clouds. In contrast to the uncertainty of the spectral line observation itself, the uncertainty of the analysis method to derive the magnetic field strength from these observations has so far not been well characterized.AimsWe investigate the impact of several physical quantities on the uncertainty of the analysis method, which is used to derive the line-of-sight (LOS) magnetic field strength from Zeeman split spectral lines. These quantities are the density, temperature, velocity, and magnetic field strength.MethodsWe simulated the Zeeman splitting of the 1665 MHz OH line with the 3D radiative transfer (RT) extension ZRAD. This extension is based on the line RT code Mol3D and has been developed for the POLArized RadIation Simulator POLARIS.ResultsObservations of the OH Zeeman effect in typical molecular clouds are not significantly affected by the uncertainty of the analysis method. However, some observations obtained a magnetic field strength of more than ~300μG, which may result in an uncertainty of the analysis method of > 10%. We derived an approximation to quantify the range of parameters in which the analysis method works accurately enough and provide factors to convert our results to other spectral lines and species as well. We applied these conversion factors to CN and found that observations of the CN Zeeman effect in typical molecular clouds are not significantly affected by the uncertainty of the analysis method. In addition, we found that the density has almost no impact on the uncertainty of the analysis method, unless it reaches values higher than those typically found in molecular clouds (nH≫ 107cm-3). Furthermore, the uncertainty of the analysis method increases if both the gas velocity and magnetic field show significant variations along the LOS. However, this increase should be small in Zeeman observations of most molecular clouds considering typical velocities of ~1 km s-1.
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DOI：
10.1051/0004-6361/201527546
发表时间：
2016-03
期刊：
arXiv: Solar and Stellar Astrophysics
影响因子：
--
作者：
R. Brauer;S. Wolf;S. Reissl
通讯作者：
R. Brauer;S. Wolf;S. Reissl
追踪 ISM 磁场形态：多波长偏振测量的潜力
影响因子：
6.5
作者：
S. Reissl;S. Wolf;D. Seifried
通讯作者：
D. Seifried
DOI：
--
发表时间：
1961
期刊：
影响因子：
--
作者：
H. Radford
通讯作者：
H. Radford
影响因子：
4.9
作者：
Crutcher, Richard M.;Hakobian, Nicholas;Troland, Thomas H.
通讯作者：
Troland, Thomas H.
DOI：
10.1016/j.jqsrt.2013.09.006
发表时间：
2014
影响因子：
2.3
作者：
R. Larsson;S. Buehler;P. Eriksson;J. Mendrok
通讯作者：
R. Larsson;S. Buehler;P. Eriksson;J. Mendrok