论文标题
尘埃极化的星际介质中磁场强度的高恰恰估计
High-accuracy estimation of magnetic field strength in the interstellar medium from dust polarization
论文作者
论文摘要
灰尘极化是研究星际介质（ISM）中磁场特性的强大工具。但是，它不能直接测量其强度。开发了不同的方法，这些方法同时采用了极化和光谱数据来推断现场强度。最广泛应用的方法是由Davis（1951），Chandrasekhar＆Fermi（1953）（DCF），Hildebrand等人开发的。 （2009）和Houde等人（2009）（HH09）。他们依赖于各向同性湍流运动引发Alvfén波的传播的假设。但是，观察结果表明，ISM中的湍流是各向异性的，非alfvénic（可压缩）模式可能很重要。我们的目标是开发一种新方法来估计ISM中的田间强度，该方法包括可压缩模式，并且与湍流的各向异性特性无矛盾。我们使用简单的能量参数考虑可压缩模式来估计磁场的强度。 We derive the following equation: $B_{0}=\sqrt{2 πρ} δv /\sqrt{δθ}$, where $ρ$ is the gas density, $δv$ is the rms velocity as derived from the spread of emission lines, and $δθ$ is the dispersion of polarization angles.我们从3D MHD模拟中产生合成观察结果，并通过将真实场强与从方程式得出的估计值进行比较来评估方法的准确性。我们发现平均相对偏差为$ 17 \％$。我们方法的准确性不取决于模拟模型的湍流特性。相反，DCF和HH09系统地高估了场强。 HH09仅对具有高声音马赫数的模拟产生准确的结果。
Dust polarization is a powerful tool for studying the magnetic field properties in the interstellar medium (ISM). However, it does not provide a direct measurement of its strength. Different methods havebeen developed which employ both polarization and spectroscopic data in order to infer the field strength. The most widely applied methods have been developed by Davis (1951), Chandrasekhar & Fermi (1953) (DCF), Hildebrand et al. (2009) and Houde et al.(2009) (HH09). They rely on the assumption that isotropic turbulent motions initiate the propagation of Alvfén waves. Observations,however, indicate that turbulence in the ISM is anisotropic and non-Alfvénic (compressible) modes may be important. Our goal is to develop a new method for estimating the field strength in the ISM, which includes the compressible modes and does not contradict the anisotropic properties of turbulence. We use simple energetics arguments that take into account the compressible modes to estimate the strength of the magnetic field. We derive the following equation: $B_{0}=\sqrt{2 πρ} δv /\sqrt{δθ}$, where $ρ$ is the gas density, $δv$ is the rms velocity as derived from the spread of emission lines, and $δθ$ is the dispersion of polarization angles. We produce synthetic observations from 3D MHD simulationsand we assess the accuracy of our method by comparing the true field strength with the estimates derived from our equation. We find a mean relative deviation of $17 \%$. The accuracy of our method does not depend on the turbulence properties of the simulated model. In contrast DCF and HH09 systematically overestimate the field strength. HH09 produces accurate results only for simulations with high sonic Mach numbers.
