http://arxiv.org/abs/2203.09745
The plane-of-the-sky component of interstellar magnetic fields can be traced in two dimensions using polarized dust emission. Its potential to access three-dimensional magnetic fields, including the inclination of the magnetic fields relative to the line-of-sight, is crucial for a variety of astrophysical problems. Based on the statistical features of the polarization fraction and the averaged POS Alfv\’en Mach number $\overline{M_{\rm A}}{,\bot}$, we present a new method for estimating the inclination angle. The magnetic field fluctuations raised by MHD turbulence are taken into account in our method. By using synthetic dust emission from 3D MHD turbulence simulation, we show that the fluctuations are preferentially perpendicular to the mean magnetic field and magnify the depolarization effect. We analytically and numerically derive that the polarization fraction is characterized by both the inclination angle and magnetic field fluctuations. We propose and demonstrate that the mean inclination angle over a region of interest can be calculated from the polarization fraction in a strongly magnetized reference position, where $\overline{M{\rm A}}{,\bot}^2\ll1$. We test the new method in sub-Alfv\’enic, trans-Alfv\’enic, and moderately super-Alfv\’enic situations ($0.4\lesssim M{\rm A}\lesssim1.2$) and show that it recovers the mean inclination angle well. This method is extended to determine the inclination angle distribution over the sub-regions of a cloud.
Y. Hu and A. Lazarian
Mon, 21 Mar 22
27/60
Comments: 10 pages, 9 figures, submitted to MNRAS
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