The effect of the galactic magnetic field on the density wave model of the spiral structure

The effect of the introduction of the galactic magnetic field on the density wave model has been studied. For this purpose a general perturbation has been introduced in the two dimensional magnetohydrodynamical equation and then wave solution of the resulting linearized equations has been considered. The amplitudes of perturbation in the density, potential velocity and magnetic fields have been calculated. The analysis suggests that the galactic magnetic field probably plays but minor role in the formation and maintenance of the large scale spiral structure of the Galaxy, although it may partly influence the motion and concentration of the gas. (author)