文章基本信息

标题：CHANG-ES
其他标题：XV. Large-scale magnetic field reversals in the radio halo of NGC 4631⋆⋆⋆
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作者：Silvia Carolina Mora-Partiarroyo ; Marita Krause ; Aritra Basu 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2019
卷号：632
页码：1-8
DOI：10.1051/0004-6361/201935961
语种：English
出版社：EDP Sciences
摘要：Aims.NGC 4631 is an interacting galaxy which exhibits one of the largest gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and polarization properties of its disk and halo emission with new radio continuum data.Methods.Radio continuum observations of NGC 4631 were performed with theKarl G. JanskyVery Large Array atC-band (5.99 GHz) in the C and D array configurations, and atL-band (1.57 GHz) in the B, C, and D array configurations. The Rotation Measure Synthesis algorithm was utilized to derive the polarization properties.Results.We detected linearly polarized emission atC-band andL-band. The magnetic field in the halo is characterized by strong vertical components above and below the central region of the galaxy. The magnetic field in the disk is only clearly seen in the eastern side of NGC 4631, where it is parallel to the plane of the major axis of the galaxy. We detected for the first time a large-scale, smooth Faraday depth pattern in a halo of an external spiral galaxy, which implies the existence of a regular (coherent) magnetic field. A quasi-periodic pattern in Faraday depth with field reversals was found in the northern halo of the galaxy.Conclusions.The field reversals in the northern halo of NGC 4631, together with the observed polarization angles, indicate giant magnetic ropes with alternating directions. To our knowledge, this is the first time such reversals are observed in an external galaxy.
关键词：engalaxies: individual: NGC 4631galaxies: halosgalaxies: magnetic fieldsgalaxies: interactionsgalaxies: spiralradio continuum: galaxies