Nonlinear galactic dynamo models with magnetic - supported interstellar gas - density stratification

We demonstrate the ability of a highly simplified galactic model to generate mean-field magnetic fields. The generated large-scale magnetic field feeds back to the vertical density stratification which itself is one of the essentials of the basic α-effect. The non-magnetic part of the stratification is due to the gravity potential of the stellar component of the galactic disk. The rotation law of the gas also results from the stellar-disk potential. A uniform turbulence field with uniform correlation time of order of 10 Myr is completing the model. The high nonlinearity in the theory determines the amplitude of the generated magnetic field. If only the conventional α-quenching is involved in the code, then the magnetic amplitude would always exceeds 10 µG in contrast to the observations (Table 4). This value is only reduced to the observed numbers of a few µG if the complete magnetic feedback is considered also in the Reynolds equation (Table 3). The magnetic field configuration is always even with respect to the equator (quadrupolar) and all models with correlation times longer than 10 Myr are oscillating. Surprisingly enough, the magnetic influence on the vertical stratification does not lead to a thicker disk. The magnetic fields in our models in general lead to a flattening of the disk. Key words: magnetohydrodynamics (MHD) – turbulence – in-terstellar medium: magnetic fields – galaxies: magnetic fields