论文标题
研究湍流和探针磁场使用梯度技术：应用于HI-H2过渡区域
Study Turbulence and Probe Magnetic Field Using Gradients Technique: Application to HI-to-H2 Transition Regions
论文作者
论文摘要
在过去的几十年中，通过分析和数值建模研究了光解离区域（PDRS）的原子至 - 分子（HI-to-H $ _2 $）过渡。但是，经典PDR模型通常假设均匀的密度气体，忽略了星际介质的湍流性质。最近，Bialy等。 （2017b，2019年）提出了一个理论框架，用于在具有非均匀密度结构的现实动荡媒介中研究HI-to-H $ _2 $。在这里，我们扩展了这些湍流化学模型，以探索使用梯度技术在湍流PDR中追踪磁场方向的可能性。我们利用化学HI/H $ _2 $余额计算的亚音速和超音速磁流体动力学模拟。我们确认湍流引起的密度波动可以分散H $ _2 $和HI分数的分布。我们发现，当声音马赫数MS增加时，力矩图的能谱变得更浅。我们探讨了高阶质心梯度的磁场追踪能力，并将其性能与传统速度质心梯度（VCG）和强度梯度（IGS）进行比较。我们发现，在探测磁场方向时，二阶质心（VC $ _2 $ GS）的速度梯度比VCG和IG更准确。
The atomic-to-molecular (HI-to-H$_2$) transition in photodissociation regions (PDRs) has been investigated over the last several decades through analytic and numerical modeling. However, classical PDR models typically assume uniform density gas, ignoring the turbulent nature of the interstellar medium. Recently, Bialy et al. (2017b, 2019) have presented a theoretical framework for studying the HI-to-H$_2$ in a realistic turbulent medium with a non-homogeneous density structure. Here we extend these turbulent-chemical models to explore the possibility of tracing the magnetic field direction in turbulent PDRs using the Gradients Technique. We utilize both subsonic and supersonic magnetohydrodynamic numerical simulations for chemical HI/H$_2$ balance calculations. We confirm that the density fluctuations induced by turbulence can disperse the distribution of H$_2$ and HI fraction. We find that the energy spectrum of moment maps gets shallower when the sonic Mach number MS increases. We explore the ability in magnetic field tracing of gradients of higher-order velocity centroids and compare their performance with that of traditional velocity centroid gradients (VCGs) and with intensity gradients (IGs). We find that the velocity gradients of the second-order centroids (VC$_2$Gs) are more accurate than VCGs and IGs in probing the magnetic field orientation.
