2023ApJ...944...86M

We have estimated the magnetic field strengths of a sample of seven galaxies using their nonthermal synchrotron radio emission at meter wavelengths, and assuming energy equipartition between magnetic fields and cosmic-ray particles. We tested for deviation of magnetic fields from energy equipartition with cosmic-ray particles, and found that deviations of ∼25% are typical for the sample galaxies. Spatially resolved star formation rates (SFRs) were estimated for the seven galaxies along with five galaxies studied previously. For the combined sample of 12 galaxies, the equipartition magnetic fields (B_eq) are correlated with the SFR surface densities (Σ_SFR) at sub-kiloparsec scales with B_eq ∝ ${{\rm{\Sigma }}}_{\mathrm{SFR}}^{0.31\pm 0.06}$, consistent with model predictions. We estimated gas densities (ρ_gas) for a subsample of seven galaxies using archival observations of the CO rotational transitions and the atomic hydrogen (H I) 21 cm line and studied the spatially resolved correlation between the magnetic fields and ρ_gas. Magnetic fields and gas densities are found to be correlated at sub-kiloparsec scale as B_eq ∝ ${\rho }_{\mathrm{gas}}^{0.40\pm 0.09}$. This is broadly consistent with models, which typically predict B ∝ ${\rho }_{\mathrm{gas}}^{0.5}$.