Magnetism in the nearby galaxy M33

TL;DR

This study investigates the structure, strength, and energy density of magnetic fields in the galaxy M33 using high-resolution polarization data and a 3-D magnetic field model, revealing complex field components and energy balance.

Contribution

It provides a detailed analysis of the magnetic field structure in M33, including the identification of axisymmetric and bisymmetric modes and the potential influence of galactic warp.

Findings

Average total magnetic field strength ~6.4 μG

Regular magnetic field strength ~2.5 μG

Turbulent and magnetic energy densities are approximately equal

Abstract

Using high-resolution data of the linearly polarized intensity and polarization angle at 3.6, 6.2, and 20 cm together with a 3-D model of the regular magnetic field, we study variations of the structure, strength, and energy density of the magnetic field in the Scd galaxy M33. The regular magnetic field consists of a horizontal component (represented by an axisymmetric mode from 1 to 3 kpc radius and a superposition of axisymmetric and bisymmetric modes from 3 to 5 kpc radius) and a vertical component. However, the inferred `vertical field' may be partly due to a galactic warp. We estimate the average total and regular magnetic field strengths as ~ 6.4 and 2.5 $\mu$G, respectively. Generation of interstellar magnetic fields by turbulent gas motion in M33 is indicated as the turbulent and magnetic energy densities are about equal.