Magnetic Fields in a Sample of Nearby Spiral Galaxies

TL;DR

This study analyzes magnetic field data from 20 nearby spiral galaxies, revealing correlations with interstellar medium parameters and comparing observations with dynamo theory to enhance understanding of galactic magnetism.

Contribution

It provides a comprehensive statistical analysis of magnetic fields in spiral galaxies, linking magnetic properties with ISM parameters and testing dynamo theory predictions.

Findings

Magnetic field strength correlates with molecular gas density and star formation rate.

Magnetic pitch angle relates to gas density, star formation, and magnetic field components.

Total and mean magnetic fields show a notable correlation, indicating a universal behavior.

Abstract

Both observations and modelling of magnetic fields in the diffuse interstellar gas of spiral galaxies are well developed but the theory has been confronted with observations for only a handful of individual galaxies. There is now sufficient data to consider statistical properties of galactic magnetic fields. We have collected data from the literature on the magnetic fields and interstellar media (ISM) of 20 spiral galaxies, and tested for various physically motivated correlations between magnetic field and ISM parameters. Clear correlations emerge between the total magnetic field strength and molecular gas density as well as the star formation rate. The magnetic pitch angle exhibits correlations with the total gas density, the star formation rate and the strength of the axisymmetric component of the mean magnetic field. The total and mean magnetic field strengths exhibit noticeable degree of correlation, suggesting a universal behaviour of the degree of order in galactic magnetic fields. We also compare the predictions of galactic dynamo theory to observed magnetic field parameters and identify directions in which theory and observations might be usefully developed.