Evaluating the Dynamical Importance of Magnetic Fields in NGC 4449

Abstract

Magnetic fields are observed in many galaxies through synchrotron radio emission and are thought to influence the structure and evolution of the interstellar medium \citep{beck2015}. Although magnetic fields in spiral galaxies have been extensively studied, their dynamical importance in irregular starburst galaxies remains less well constrained \citep{beck2015}. 

NGC 4449 is a Magellanic-type irregular galaxy undergoing enhanced star formation activity and exhibiting strong nonthermal radio emission, indicating the presence of a measurable galactic magnetic field \citep{chyzy2000}. Previous radio polarization studies estimate a total magnetic field strength of approximately 10–15 $\mu$G in this system \citep{chyzy2000}. 

In this study, we evaluate whether the magnetic field in NGC 4449 is dynamically significant by comparing its magnetic energy to the turbulent kinetic energy of the gas and the gravitational binding energy of the galaxy \citep{hunter1999}. Using literature values for magnetic field strength, gas mass, velocity dispersion, total dynamical mass, and galactic radius, we calculate the magnetic energy density using classical electromagnetic theory and estimate total energies assuming a spherical approximation \citep{beck2015}. 

Our calculations show that the magnetic energy constitutes a non-negligible fraction of the gravitational binding energy, reaching up to several percent of the total binding energy of the galaxy \citep{chyzy2000}. The turbulent kinetic energy is found to be comparable in magnitude to the magnetic energy, suggesting that both processes contribute to supporting the interstellar medium against gravitational collapse \citep{hunter1999}. 

These results indicate that while gravity dominates the global structure of NGC 4449, magnetic fields likely play a dynamically relevant role in regulating gas motions and star formation in this irregular galaxy \citep{beck2015}. Our findings highlight the importance of including magnetic fields in simplified dynamical models of irregular starburst systems.