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