Large-scale magnetic field structure of NGC 3627 based on magnetic vector map

TL;DR

This study maps and analyzes the large-scale magnetic field structure of galaxy NGC 3627 using polarization data, revealing a bi-symmetric spiral pattern aligned with spiral arms and suggesting magnetic field generation via parametric resonance.

Contribution

It introduces a magnetic vector reconstruction method to NGC 3627 and characterizes its magnetic field mode, providing new insights into galaxy magnetic field structures.

Findings

Magnetic field aligns with spiral arms.

Magnetic field exhibits bi-symmetric spiral structure.

Magnetic mode number is m_B=1 in outer regions.

Abstract

We analyzed the data of Stokes $I$, $Q$, and $U$ in C- and X-bands and investigated the large-scale magnetic field structure of NGC 3627. The polarization intensity and angle in each band were derived using Stokes $Q$ and $U$ maps. The rotation measure was calculated using the polarization-angle maps. Moreover, the magnetic field strength was calculated by assuming energy equipartition with the cosmic ray electrons. The structure of the magnetic field was well aligned with the spiral arms, which were consistent with those in the former studies. We applied the magnetic vector reconstruction method to NGC 3627 to derive a magnetic vector map, which showed that northern and southern disks were dominant with inward and outward magnetic vectors, respectively. Furthermore, we discussed the large-scale structure of the magnetic field in NGC 3627 and observed that the structure is bi-symmetric spiral in nature, and that the number of magnetic field mode is $ m_{\rm B} = 1 $ in outer region of galaxy. In addition, NGC 3627 has a mode of two spiral arms that were clearly visible in an optical image. The ratio of the mode of spiral arms to that of magnetic field is 2:1. In terms of NGC 3627, the large-scale magnetic field may be generated via the parametric resonance induced by the gravitational potential of the spiral arms.