|Beschreibung:||In the first part of the thesis at hand, the relation between vertical magnetic fields and dark matter in disc galaxies is studied. Under the assumption that the studied perturbations in these galaxies are stationary, we derive a mathematical relation between the mass of the dark matter and the magnetic field strength. Thereby, we find that already medium magnetic field strengths strongly correlate with the mass of the dark matter. A slight enhancement of the magnetic field can already destroy the stationarity of a composition. Vice versa a stationary structure can be produced by variation of the magnetic field strength.
In the second part the time evolution of an isolated galaxy by means of the N-body / SPH (smoothed particle hydrodynamics) code GADGET-2 is studied numerically.
By applying three different methods, we try to produce long-lived density waves in the disc, which lead to the so-called `grand-design' structure. Star formation and stellar feedback in terms of supernova explosions are included.
All three methods are able to produce the desired grand-design spiral structures. However, the structures disappear after a short time span.
With several examples, we show that the reason for the fast disappearance lies in the nature of the spiral arms.
The created spiral arms are always material arms but not the required classical density waves of the density wave theory. Material arms consist of the same particles and wind up with time. This is visible in the simulation results.
The reasons for the absence of the density wave and further simulations to be done are discussed finally.