Equipartition magnetic fields and star formation rates in normal galaxies at sub-kpc scales

TL;DR

This study investigates magnetic field strengths in normal star-forming galaxies at sub-kiloparsec scales, confirming the equipartition assumption and revealing strong correlations with star formation rates and energy densities.

Contribution

It demonstrates the validity of the equipartition assumption at sub-kpc scales and links magnetic fields to star formation activity in galaxies.

Findings

Magnetic field strength correlates with surface star formation rate.

Magnetic energy density is comparable to gas energy density in star-forming regions.

Magnetic fields dominate in regions of low star formation efficiency.

Abstract

We studied the total magnetic field strength in normal star-forming galaxies estimated using energy equipartition assumption. Using the well known radio--far infrared correlation we demonstrate that the equipartition assumption is valid in galaxies at sub-kpc scales. We find that the magnetic field strength is strongly correlated with the surface star formation rate in the galaxies NGC 6946 and NGC 5236. Further, we compare the magnetic field energy density to the total (thermal + turbulent) energy densities of gas (neutral + ionized) to identify regions of efficient field amplification in the galaxy NGC 6946. We find that in regions of efficient star formation, the magnetic field energy density is comparable to that of the total energy density of various interstellar medium components and systematically dominates in regions of low star formation efficiency.