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arXiv · 2004.14383

CHANG-ES XXII: Coherent Magnetic Fields in the Halos of Spiral Galaxies

Marita Krause·Judith Irwin·Philip Schmidt·Yelena Stein·Arpad Miskolczi·Silvia Carolina Mora-Partiarroyo·Theresa Wiegert·Rainer Beck·Jeroen M. Stil·George Heald·Jiang-Tao Li·Ancor Damas-Segovia·Carlos J. Vargas·Richard J. Rand·Jennifer West·Rene A. M. Walterbos·Ralf-Jürgen Dettmar·Jayanne English·Alex Woodfinden
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Abstract

Context. The magnetic field in spiral galaxies is known to have a large-scale spiral structure along the galactic disk and is observed as X-shaped in the halo of some galaxies. While the disk field can be well explained by dynamo action, the 3-dimensional structure of the halo field and its physical nature is still unclear. Aims. As first steps towards understanding the halo fields, we want to clarify whether the observed X-shaped field is a wide-spread pattern in the halos of spiral galaxies and whether these halo fields are just turbulent fields ordered by compression or shear (anisotropic turbulent fields), or have a large-scale regular structure. Methods. The analysis of the Faraday rotation in the halo is the tool to discern anisotropic turbulent fields from large-scale magnetic fields. This, however, has been challenging until recently because of the faint halo emission in linear polarization. Our sensitive VLA broadband observations C-band and L-band of 35 spiral galaxies seen edge-on (called CHANG-ES) allowed us to perform RM-synthesis in their halos and to analyze the results. We further accomplished a stacking of the observed polarization maps of 28 CHANG-ES galaxies at C-band. Results. Though the stacked edge-on galaxies were of different Hubble types, star formation and interaction activities, the stacked image clearly reveals an X-shaped structure of the apparent magnetic field. We detected a large-scale (coherent) halo field in all 16 galaxies that have extended polarized intensity in their halos. We detected large-scale field reversals in all of their halos. In six galaxies they are along lines about vertical to the galactic midplane (vertical RMTL) with about 2 kpc separation. Only in NGC 3044 and possibly in NGC 3448 we observed vertical giant magnetic ropes (GMRs) similar to those detected recently in NGC 4631.

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Marita Krause, Judith Irwin, Philip Schmidt, Yelena Stein, Arpad Miskolczi, Silvia Carolina Mora-Partiarroyo, Theresa Wiegert, Rainer Beck, Jeroen M. Stil, George Heald, Jiang-Tao Li, Ancor Damas-Segovia, Carlos J. Vargas, Richard J. Rand, Jennifer West, Rene A. M. Walterbos, Ralf-Jürgen Dettmar, Jayanne English, Alex Woodfinden. 2020-04-29. CHANG-ES XXII: Coherent Magnetic Fields in the Halos of Spiral Galaxies. https://doi.org/10.1051/0004-6361/202037780

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