# Magnetic field vector maps of nearby spiral galaxies

## TL;DR

This paper introduces a cost-effective method to determine magnetic field directions in spiral galaxies using polarization maps and velocity data, revealing complex magnetic structures and reversals.

## Contribution

The paper presents a novel, simple approach to map magnetic field vectors in spiral galaxies using existing observational data, resolving the 180° ambiguity efficiently.

## Key findings

- Magnetic fields in the studied galaxies are more complex than simple axis-symmetric models.
- Magnetic reversals are common in the analyzed galaxies.
- The method successfully applied to archival VLA data.

## Abstract

We present a method for determining directions of magnetic field vectors in a spiral galaxy using two synchrotron polarization maps, an optical image, and a velocity field. The orientation of the transverse magnetic field is determined with a synchrotron polarization map of higher frequency band and the $180^\circ$-ambiguity is solved by using sign of the Rotation Measure (RM) after determining geometrical orientation of a disk based on a assumption of trailing spiral arms. The advantage of this method is that direction of magnetic vector for each line of sight through the galaxy can be inexpensively determined with easily available data and with simple assumptions. We applied this method to three nearby spiral galaxies using archival data obtained with the Very Large Array (VLA) to demonstrate how it works. The three galaxies have both clockwise and counter-clockwise magnetic fields, which implies that all three galaxies are not classified in simple Axis-Symmetric type but types of higher modes and that magnetic reversals commonly exist.