CHANG-ES XXI。NGC 4217的输运过程和X形磁场：偏心超磁泡结构
CHANG-ES XXI. Transport processes and the X-shaped magnetic field of NGC 4217: off-center superbubble structure
摘要：
为了更好地了解宇宙射线和磁场对边旋星系盘晕界面的影响，我们利用CHANG-ES在6 GHz（C波段）和1.5GHz（L波段）两个频率的射电观测资料，研究了边旋星系NGC 4217的射电连续晕、磁场和宇宙线的输运过程。以及150 MHz的LOFAR补充数据和X射线钱德拉数据。NGC 4217显示了一个大尺度的X形磁场结构，覆盖了星系的大部分，平均总磁场强度为9微高斯（通过均分）。利用旋转测度合成（RM合成）在C波段，我们发现，磁盘的磁场的方向指向内。此外，在星系的西北部还存在一个螺旋流出结构，它延伸到晕内近7千秒差距。在星系靠近的一侧观察到更多的偏振发射。通过一个简化的星系盘模型，我们能够解释这一发现，并预测大约75%的边缘螺旋星系将在接近的一侧显示出更高的偏振强度。在C波段的总强度中发现了许多环和壳结构。一个超气泡状的结构在总强度和偏振强度，以及Halpha和光学尘埃丝中都很突出，这可能是星盘中集中恒星形成的结果。与晕相比，盘的通量密度贡献朝向较低频率减小。在三个射频的总强度分布与双分量指数函数拟合。C-波段和L-波段之间的尺度高度的频率依赖性表明平流是主要的CR运输过程。一维CR输运模型（SPINNAKER）表明，平流似乎比扩散更重要。
英文摘要：
In order to gain a better understanding of the influence of cosmic rays (CRs) and magnetic fields in the disk-halo interface of edge-on spiral galaxies, we investigate the radio continuum halo, the magnetic field, and the transport processes of the CRs of the edge-on spiral galaxy NGC 4217 using CHANG-ES radio data at two frequencies, 6 GHz (C-band) and 1.5 GHz (L-band), and supplemental LOFAR data at 150 MHz and X-ray Chandra data. NGC 4217 shows a large-scale X-shaped magnetic field structure, covering a major part of the galaxy with a mean total magnetic field strength in the disk of 9 micro Gauss (via equipartition). Using rotation measure synthesis (RM-synthesis) at C-band, we found that the direction of the disk magnetic field is pointing inward. A helical outflow structure is furthermore present in the northwestern part of the galaxy, which is extended nearly 7 kpc into the halo. More polarized emission is observed on the approaching side of the galaxy. With a simplified galaxy disk model, we are able to explain that finding and predict that roughly 75% of edge-on spiral galaxies will show higher polarized intensity on the approaching side. Many loop and shell structures are found throughout the galaxy in total intensity at C-band. A superbubble-like structure is prominent in total and polarized intensity, as well as in Halpha and optical dust filaments, being a possible result of concentrated star formation in the disk. The flux density contribution of the disk in comparison to the halo decreases toward lower frequencies. Total intensity profiles at the three radio frequencies were fit with two-component exponential functions. The frequency dependence of the resulting scale heights between C-band and L-band suggests advection to be the main CR transport process. The 1D CR transport modeling (SPINNAKER) shows that advection appears to be more important than diffusion.
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