Non-linear dynamo action and disc-halo interaction in disc galaxies

摘要

We present an observationally constrained model of mass outflow for galactic discs, derived from star formation rate. This is used to supplement a model of the non-linear, mean-field, α2Ω galactic dynamo in the presence of shear. Outflows affect the magnetic pitch angles unexpectedly. This resolves a long standing problem in non-linear dynamo theory, marking a fundamental improvement in the degree of agreement with observations. The mean-field equations are reduced using a modified version of the no-z approximation, to allow for observed flaring of gaseous galactic discs, leaving us with a flared thin-disc model. We have explored two non-linearities to describe the α-effect. We use recent spatially dependent observations of various galaxy properties to evolve the dynamo equations in time. We present results of the steady state magnetic field for both nonlinearities and demonstrate that observables such as local magnetic field strength and magnetic pitch angle can be closely reproduced, using optimum, physically acceptable values of outflow velocity. We apply the model to a number of well observed galactic systems with similar kinematic properties and discuss several sensitivities of the model whilst modifying data sets within the ranges of observational uncertainty.