利用差分测量方法和速度通道图获取磁场强度
Obtaining magnetic field strength using differential measure approach and velocity channel maps
摘要：
本文介绍了两种同时利用光谱多普勒频移谱线和磁场方向信息获得天平面（POS）磁场强度的新方法。后者可以通过偏振测量或使用速度梯度技术来获得。我们的技术相比，传统的Davis-Davrasekhar-Fermi（DCF）技术的观测估计磁场强度的优势。我们详细描述的第一种技术采用的结构函数的速度质心和斯托克斯参数的结构函数。我们提供了从观测数据中获得磁场强度的解析表达式。我们成功地测试我们的结果使用合成观测MHD湍流模拟的结果。我们测量速度和磁场波动在小尺度上使用两个，三个和四个点的结构函数，并比较这些工具的性能。我们表明，与DCF不同，我们的技术能够提供POS磁场的详细分布，它可以测量磁场强度中存在的速度和磁场扭曲所产生的外部剪切和自重。第二种方法将速度梯度技术应用于速度通道图，以获得阿尔芬马赫数，并利用梯度的幅值获得音速马赫数。这两个马赫数的比率提供了通道图中对发射有贡献的区域中的磁场的强度。我们对该技术进行了测试，并讨论了用该技术获取POS星系磁场的三维分布，讨论了第二种技术在同步辐射数据中的应用。
英文摘要：
We introduce two new ways of obtaining the strength of plane-of-sky (POS) magnetic field by simultaneous use of spectroscopic Doppler-shifted lines and the information on magnetic field direction. The latter can be obtained either through polarization measurements or using the velocity gradient technique. We show the advantages that our techniques have compared to the traditional Davis-Chandrasekhar-Fermi (DCF) technique of estimating magnetic field strength from observations. The first technique that we describe in detail employs structure functions of velocity centroids and structure functions of Stokes parameters. We provide analytical expressions for obtaining magnetic field strength from observational data. We successfully test our results using synthetic observations obtained with results of MHD turbulence simulations. We measure velocity and magnetic field fluctuations at small scales using two, three and four point structure functions and compare the performance of these tools. We show that, unlike the DCF, our technique is capable of providing the detailed distribution of POS magnetic field and it can measure magnetic field strength in the presence of both velocity and magnetic field distortions arising from external shear and self-gravity. The second technique applies the velocity gradient technique to velocity channel maps in order to obtain the Alfven Mach number and uses the amplitudes of the gradients to obtain the sonic Mach number. The ratio of these two Mach numbers provides the intensity of magnetic field in the region contributing to the emission in the channel map. We test the technique and discuss obtaining the 3D distribution of POS galactic Magnetic field with it. We discuss the application of the second technique to synchrotron data.
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