Magnetic fields in the outer rings of spiral galaxies

摘要

Now there is no doubt that at least in some spiral galaxies there are regular magnetic fields of several μG. Their generation is described by the so-called dynamo mechanism that is based on differential rotation and turbulent motions of the interstellar medium. Some galaxies have outer rings where there is some ionized gas. So the magnetic field can exist in the outer rings, too. To model these magnetic fields we use the so-called no-z model that is based on the small thickness of the disc. z-Derivatives can be replaced by algebraic expressions and the z-component of the field can be neglected. We have found that the magnetic field can be generated in rings that have half- width more than 1 kpc. However, even if the field generation in situ is impossible, the magnetic field can pass to the outer rings by a Kolmogorov-Petrovsky-Piskunov effect.