Magnetic fields in galaxies: I. Radio disks in local late-type galaxies

TL;DR

This paper presents an analytical model for the evolution of magnetic fields in disk galaxies, emphasizing the role of turbulence, gas dynamics, and galactic rotation, and compares predictions with observations of local late-type galaxies.

Contribution

It introduces a new analytical framework that models magnetic field amplification in galaxies considering turbulence, gas infall, star formation, and rotation effects, aligning with observed data.

Findings

Model accurately predicts magnetic field strengths in low and intermediate-mass galaxies.

Overestimates magnetic fields in massive galaxies, indicating the need for additional processes like AGN feedback.

Highlights the importance of turbulence and rotation in magnetic field evolution.

Abstract

We develop an analytical model to follow the cosmological evolution of magnetic fields in disk galaxies. Our assumption is that fields are amplified from a small seed field via magnetohydrodynamical (MHD) turbulence. We further assume that this process is fast compared to other relevant timescales, and occurs principally in the cold disk gas. We follow the turbulent energy density using the Shabala & Alexander (2009) galaxy formation and evolution model. Three processes are important to the turbulent energy budget: infall of cool gas onto the disk and supernova feedback increase the turbulence; while star formation removes gas and hence turbulent energy from the cold gas. Finally, we assume that field energy is continuously transferred from the incoherent random field into an ordered field by differential galactic rotation. Model predictions are compared with observations of local late type galaxies by Fitt & Alexander (1993) and Shabala et al. (2008). The model reproduces observed magnetic field strengths and luminosities in low and intermediate-mass galaxies. These quantities are overpredicted in the most massive hosts, suggesting that inclusion of gas ejection by powerful AGNs is necessary in order to quench gas cooling and reconcile the predicted and observed magnetic field strengths.