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首页> 外文期刊>Astronomy and astrophysics >Cosmic rays and the magnetic field in the nearby starburst galaxy NGC?253 - II. The magnetic field structure
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Cosmic rays and the magnetic field in the nearby starburst galaxy NGC?253 - II. The magnetic field structure

机译：邻近星爆星系NGC？253-II的宇宙射线和磁场。磁场结构

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Context. There are several edge-on galaxies with a knownmagnetic field structure in their halo. A vertical magnetic fieldsignificantly enhances the cosmic-ray transport from the disk into thehalo. This could explain the existence of the observed radio halos. Aims. We observed NGC253 that possesses one of thebrightest radio halos discovered so far. Since this galaxy is notexactly edge-on ()the disk magnetic field has to be modeled and subtracted from theobservations in order to study the magnetic field in the halo. Methods. We used radio continuum polarimetry with the VLA inD-configuration and the Effelsberg 100-m telescope. NGC253 has avery bright nuclear point-like source, so that we had to correct forinstrumental polarization. We used appropriate Effelsberg beam patternsand developed a tailored polarization calibration to cope with theoff-axis location of the nucleus in the VLA primary beams. Observationsat 6.2cm and 3.6cm were combined to calculate the RM distribution and to correct for Faraday rotation. Results. The large-scale magnetic field consists of a disk and a halo(r,z) component. The disk component can be described as an axisymmetric spiral field pointing inwards with a pitch angle of which is symmetricwith respect to the plane (even parity). This field dominates in thedisk, so that the observed magnetic field orientation is disk parallelat small distances from the midplane. The halo field shows a prominentX-shape centered on the nucleus similar to that of other edge-ongalaxies. We propose a model where the halo field lines are along acone with an opening angle of and are pointing away from the disk in both the northern and southernhalo (even parity). We can not exclude that the field points inwards inthe northern halo (odd parity). The X-shaped halo field follows thelobes seen in Hand soft X-ray emission. Conclusions. Dynamo action and a disk wind can explain theX-shaped halo field. The nuclear starburst-driven superwind may furtheramplify and align the halo field by compression of the lobes of theexpanding superbubbles. The disk wind is a promising candidate for theorigin of the gas in the halo and for the expulsion of small-scalehelical fields as requested for efficient dynamo action. Key words: galaxies: individual: NGC253 - magnetic fields - methods: observational - methods: data analysis - galaxies: halos - galaxies: ISM
机译：上下文。有几个边缘晕星系的光环中具有已知的磁场结构。垂直磁场显着增强了从磁盘到光晕的宇宙射线传输。这可以解释观察到的无线电晕的存在。目的我们观察到NGC253拥有迄今为止发现的最明亮的无线电晕之一。由于该星系并非精确地在边缘上，因此必须对磁盘磁场建模并从观测中减去，以便研究光晕中的磁场。方法。我们在VLA inD配置和Effelsberg 100-m望远镜中使用了连续波极化仪。 NGC253具有非常明亮的核点状光源，因此我们必须校正仪器极化。我们使用了合适的Effelsberg光束模式，并开发了量身定制的偏振校准，以应对VLA主光束中原子核的偏轴位置。结合在6.2cm和3.6cm处的观测值来计算RM分布并校正法拉第旋转。结果。大规模磁场由一个磁盘和一个晕（r，z）分量组成。圆盘组件可以描述为一个轴对称螺旋场，该场向内指向，其螺距角相对于该平面对称（均匀）。该磁场在磁盘中占主导地位，因此观察到的磁场方向是磁盘，与磁盘的中平面距离很小。晕场显示出一个以核为中心的显着X形，类似于其他边缘非畸变。我们提出了一个模型，其中晕圈线沿着圆锥形，其开口角为，并且在北晕和南晕（甚至奇偶校验）中都指向远离圆盘的方向。我们不能排除磁场指向北晕（奇偶校验）的方向。 X形的光晕场跟随手部软X射线发射中看到的波瓣。结论。发电机的动作和盘状风可以解释X形的光晕场。核爆炸形驱动的超风可通过压缩膨胀的超气泡的波瓣来进一步放大并对准晕场。圆盘风是光晕中气体起源和驱逐小规模螺旋场的有前途的候选者，这是有效的发电机作用所要求的。关键词：星系：个人：NGC253-磁场-方法：观测-方法：数据分析-星系：光晕-星系：ISM

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