Resolved magnetic structures in the disk-halo interface of NGC 628
Resolved magnetic structures in the disk-halo interface of NGC 628
复制标题
NGC 628 盘-晕界面中的磁结构解析
DOI：
10.1051/0004-6361/201629907
复制
发表时间：
2017
影响因子：
6.5
通讯作者：
Mulcahy
中科院分区：
文献类型：
--
作者：
Mulcahy
背景磁场对于充分理解星际介质是必不可少的，它在星系盘-晕界面中的作用仍然知之甚少。恒星的形成可以垂直地将热气体逐出到晕中，这些热气体的流出对平均场发电机理论具有重要的意义，因为它们可以有效地消除磁螺旋。目的我们的目的是探测垂直磁场，并加深我们对星系盘-晕相互作用的理解。研究面对面的星系对于分离三维空间中的磁场分量是非常必要的。方法我们用KarlG.Jansky超大型阵列ATS波段(有效带宽2.6-3.6 GHz)和Effelsberg100m望远镜对附近的面对面螺旋星系NGC 6 2 8进行了新的观测，频率分别为2.6 GHz和8.35 GHz，带宽分别为80 GHz和1.1 GHz。由于JVLA接收系统的带宽很大，我们获得了迄今为止观测到的任何外部星系的总偏振强度和线偏振强度的一些最敏感的射电连续图像。结果旋转测量合成应用于在这个大带宽上的干涉偏振数据提供了高质量的法拉第深度和偏振角的图像，从这些图像我们获得了盘-晕连接中磁湍流的驱动因素的证据。这样的驱动因素包括通过与HI洞重合的显著法拉第深度梯度探测到的超级气泡。我们在法拉第深度观察到方位角周期花样，其花样波长为3.7 ± 0.1kpc，表明帕克不稳定性。法拉第深度和磁俯仰角之间没有显著的反相关性，这表明这些环路本质上是垂直的，几乎没有螺旋扭曲，与IC 342中不同。我们发现，磁场的俯仰角系统地大于极化臂的形态俯仰角，这证明了规则磁场不与气流耦合的大型发电机的作用，并获得了显著的径向分量。此外，我们还在银河系北部发现了一个偏振度高、俯仰角小的有序磁场孤立区，这一特征是迄今在任何其他星系中都没有观察到的，可能是由一个不对称的H-I洞引起的。结论到目前为止，NGC- 628在射电连续谱中相对没有被探索过，但由于其扩展的H-I盘以及其中心区域缺乏活动恒星的形成，已经产生了丰富的有趣的磁现象。我们观察到了NgC628盘-晕连接中磁湍流的两个驱动因素，即 不稳定性和超泡。
ContextMagnetic fields are essential to fully understand the interstellar medium and its role in the disk-halo interface of galaxies is still poorly understood. Star formation is known to expel hot gas vertically into the halo and these outflows have important consequences for mean-field dynamo theory in that they can be efficient in removing magnetic helicity.AimsWe aim to probe the vertical magnetic field and enhance our understanding of the disk-halo interaction of galaxies. Studying a face-on galaxy is essential so that the magnetic field components can be separated in 3D.MethodsWe perform new observations of the nearby face-on spiral galaxy NGC 628 with theKarl G. JanskyVery Large Array (JVLA) atS-band (2.6–3.6 GHz effective bandwidth) and the Effelsberg 100-m telescope at frequencies of 2.6 GHz and 8.35 GHz with a bandwidth of 80 MHz and 1.1 GHz, respectively. Owing to the large bandwidth of the JVLA receiving system, we obtain some of the most sensitive radio continuum images in both total and linearly polarised intensity of any external galaxy observed so far.ResultsThe application of rotation measures synthesis to the interferometric polarisation data over this large bandwidth provides high-quality images of Faraday depth and polarisation angle from which we obtained evidence for drivers of magnetic turbulence in the disk-halo connection. Such drivers include a superbubble detected via a significant Faraday depth gradient coinciding with a H I hole. We observe an azimuthal periodic pattern in Faraday depth with a pattern wavelength of 3.7 ± 0.1 kpc, indicating Parker instabilities. The lack of a significant anti-correlation between Faraday depth and magnetic pitch angle indicates that these loops are vertical in nature with little helical twisting, unlike in IC 342. We find that the magnetic pitch angle is systematically larger than the morphological pitch angle of the polarisation arms which gives evidence for the action of a large-scale dynamo where the regular magnetic field is not coupled to the gas flow and obtains a significant radial component. We additionally discover a lone region of ordered magnetic field to the north of the galaxy with a high degree of polarisation and a small pitch angle, a feature that has not been observed in any other galaxy so far and is possibly caused by an asymmetric H I hole.ConclusionsUntil now NGC 628 has been relatively unexplored in radio continuum but with its extended H I disk and lack of active star formation in its central region has produced a wealth of interesting magnetic phenomena. We observe evidence for two drivers of magnetic turbulence in the disk-halo connection of NGC 628, namely, Parker instabilities and superbubbles.
登录
查看更多内容
对六个附近正常星系的 GMRT 333 MHz 观测
DOI：
--
发表时间：
2011
期刊：
影响因子：
--
作者：
A. Basu;D. Mitra;Y. Wadadekar;C. Ishwara
通讯作者：
C. Ishwara
恒星形成星系的同步加速器光谱指数和星际介质密度
影响因子：
4.8
作者：
A. Basu;R. Beck;P. Schmidt;Subhashis Roy
通讯作者：
Subhashis Roy
VLASS 提案分析
DOI：
--
发表时间：
2015
期刊：
影响因子：
--
作者：
J. Condon
通讯作者：
J. Condon
科里奥利力和磁重联影响下帕克不稳定星系磁场的拓扑演化
DOI：
--
发表时间：
2002
期刊：
影响因子：
--
作者：
M. Hanasz;K. Otmianowska;H. Lesch
通讯作者：
H. Lesch
仙女座星系 H-alpha 和远红外线的两个视图
DOI：
--
发表时间：
1994
期刊：
影响因子：
--
作者：
N. Devereux;R. Price;L. Wells;N. Duric
通讯作者：
N. Duric