Technique for Separating Velocity and Density Contributions in Spectroscopic Data and Its Application to Studying Turbulence and Magnetic Fields
Technique for Separating Velocity and Density Contributions in Spectroscopic Data and Its Application to Studying Turbulence and Magnetic Fields
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DOI：
10.3847/1538-4357/abe4d4
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发表时间：
2020-12
期刊：
影响因子：
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通讯作者：
K. Yuen;K. Ho;A. Lazarian
中科院分区：
文献类型：
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作者：
K. Yuen;K. Ho;A. Lazarian
基于Lazarian和Pogosyan关于位置-位置-速度(PPV)统计的理论描述，我们引入了一种新的技术，称为速度分解算法(VDA)，用于分离由速度和密度涨落引起的PPV涨落。利用MHD湍流模拟，我们展示了它在从PPV立方体中提取各种物理条件下的速度涨落的前景以及它在精确跟踪磁场方面的前景。我们发现，对于局域云，速度涨落在谱线的翼部最为突出，它们主导着密度涨落。同样的速度优势也适用于经历银河系自转的延长的HI区。我们的数值实验表明，氢原子冷相产生的速度通道仍然受到小尺度速度涨落的影响。我们将VDA应用于对应于高速云HVC186+19-114的HI GALFA-DR2数据和高纬星系扩散HI数据。我们的研究证实了速度波动在解释为什么在PPV立方体中观察到线性结构方面起到了至关重要的作用。我们讨论了VDA对于磁场研究和作为宇宙微波背景研究前景的极化星系发射的预测的意义。此外，我们还讨论了与HI通道图的丝状性质有关的争议，并解释了速度波动在PPV数据立方体结构形成中的重要性。VDA将允许天文学家从几乎每一条PPV光谱数据中获得速度波动，并允许在观测中直接研究湍流速度场。
Based on the theoretical description of position–position–velocity (PPV) statistics in Lazarian & Pogosyan, we introduce a new technique called the velocity decomposition algorithm (VDA) for separating the PPV fluctuations arising from velocity and density fluctuations. Using MHD turbulence simulations, we demonstrate its promise in retrieving the velocity fluctuations from the PPV cube in various physical conditions and its prospects in accurately tracing the magnetic field. We find that for localized clouds, the velocity fluctuations are most prominent in the wing part of the spectral line, and they dominate the density fluctuations. The same velocity dominance applies to extended H i regions undergoing galactic rotation. Our numerical experiment demonstrates that velocity channels arising from the cold phase of atomic hydrogen (H i) are still affected by velocity fluctuations at small scales. We apply the VDA to H i GALFA-DR2 data corresponding to the high-velocity cloud HVC186+19-114 and high-latitude galactic diffuse H i data. Our study confirms the crucial role of velocity fluctuations in explaining why linear structures are observed within PPV cubes. We discuss the implications of VDA for both magnetic field studies and predicting polarized galactic emission that acts as the foreground for cosmic microwave background studies. Additionally, we address the controversy related to the filamentary nature of the H i channel maps and explain the importance of velocity fluctuations in the formation of structures in PPV data cubes. VDA will allow astronomers to obtain velocity fluctuations from almost every piece of spectroscopic PPV data and allow direct investigations of the turbulent velocity field in observations.