Magnetic Fields, Star Formation Rates and Gas Densities at Sub-kpc Scales in a Pilot Sample of Nearby Galaxies

Abstract

We have estimated the magnetic field strengths of a sample of seven galaxies using their non-thermal synchrotron radio emission at metre wavelengths, and assuming energy equipartition between magnetic fields and cosmic ray particles. Spatially resolved star formation rates (SFR) were estimated for the seven galaxies along with five galaxies studied previously. For the combined sample of twelve galaxies, the equipartition magnetic fields (B$_\textrm{eq}$) are correlated with the SFR surface densities ($\Sigma_\textrm{SFR}$) at sub-kpc scales with B$_\textrm{eq}$ $\propto$ $\Sigma_\textrm{SFR}^ {0.31\pm0.06}$, consistent with model predictions. We estimated gas densities ($\rho_\textrm{gas}$) for a sub-sample of seven galaxies using archival observations of the carbon monoxide (CO) rotational transitions and the atomic hydrogen (HI) 21 cm line and studied the spatially-resolved correlation between the magnetic fields and $\rho_\textrm{gas}$. Magnetic fields and gas densities are found to be correlated at sub-kpc scale as B$_\textrm{eq}$ $\propto$ $\rho_\textrm{gas}^{0.40\pm0.09}$. This is broadly consistent with models, which typically predict B $\propto$ $\rho_\textrm{gas}^{0.5}$.