The Galactic Magneto-ionic Medium Survey: Moments of the Faraday Spectra
The Galactic Magneto-ionic Medium Survey: Moments of the Faraday Spectra
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DOI：
10.3847/1538-4357/aaf85f
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发表时间：
2018-12
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通讯作者：
J. Dickey;T. Landecker;A. Thomson;M. Wolleben;Xiaohui Sun;E. Carretti;Kevin A. Douglas;A. Fletcher;B. Gaensler;A. Gray;M. Haverkorn;A. Hill;A. Hill;A. Hill;S. A. Mao;N. McClure-Griffiths
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作者：
J. Dickey;T. Landecker;A. Thomson;M. Wolleben;Xiaohui Sun;E. Carretti;Kevin A. Douglas;A. Fletcher;B. Gaensler;A. Gray;M. Haverkorn;A. Hill;A. Hill;A. Hill;S. A. Mao;N. McClure-Griffiths
法拉第旋转沿着银河系的每条视线发生;旋转测量（RM）合成允许星际磁场的3D表示。这项研究使用的数据来自全球磁离子介质调查，这是单天线光谱偏振研究的组合，包括来自自治领射电天体物理观测台26米望远镜（1270-1750兆赫）的北方天空数据和来自帕克斯64米望远镜（300-480兆赫）的南方天空数据。从合成的法拉第光谱立方体，我们计算零阶，第一，第二时刻，找到总偏振发射，平均RM，RM宽度的偏振发射。从DRAO的第一时刻，我们发现一个弱的垂直场从银河系北到南，但帕克斯的数据显示，在两个半球的高纬度地区，指向太阳的领域：这两个调查显然采样不同的体积。DRAO二阶矩显示法拉第光谱的特征宽度随着正纬度的降低而增加，这意味着较长的视线遇到更多的法拉第旋转介质，但这在负纬度处看不到。Parkes的数据显示了相反的情况：在正纬度，二阶矩随着纬度的减小而减小，但在负纬度则不然。将一阶矩与银河系和河外源的RM进行比较，并对去极化进行研究，共同证实了DRAO调查的采样距离比Parkes数据更远。在DRAO勘测中的发射区域通常在700-1000 pc的距离，稍微超出磁离子介质的标度高度;在帕克斯勘测中检测到的发射完全在磁离子盘内，距离不到500 pc。
Faraday rotation occurs along every line of sight in the Galaxy; rotation measure (RM) synthesis allows a 3D representation of the interstellar magnetic field. This study uses data from the Global Magneto-Ionic Medium Survey, a combination of single-antenna spectro-polarimetric studies, including northern sky data from the Dominion Radio Astrophysical Observatory (DRAO) 26 m telescope (1270–1750 MHz) and southern sky data from the Parkes 64 m telescope (300–480 MHz). From the synthesized Faraday spectral cubes we compute the zeroth, first, and second moments to find the total polarized emission, mean RM, and RM width of the polarized emission. From DRAO first moments we find a weak vertical field directed from Galactic North to South, but Parkes data reveal fields directed toward the Sun at high latitudes in both hemispheres: the two surveys clearly sample different volumes. DRAO second moments show feature widths in Faraday spectra increasing with decreasing positive latitudes, implying that longer lines of sight encounter more Faraday rotating medium, but this is not seen at negative latitudes. Parkes data show the opposite: at positive latitudes the second moment decreases with decreasing latitude, but not at negative latitudes. Comparing first moments with RMs of pulsars and extragalactic sources and a study of depolarization together confirm that the DRAO survey samples to larger distances than the Parkes data. Emission regions in the DRAO survey are typically 700–1000 pc away, slightly beyond the scale height of the magneto-ionic medium; emission detected in the Parkes survey is entirely within the magneto-ionic disk, less than 500 pc away.