The magnetic field evolution in a spiral galaxy is shown. The velocity and density distribution are obtained from a particle simulation with gas clouds and stars. The time evolution of gas velocity and density are taken as the input for the induction equation to follow the magnetic field evolution under the action of a turbulent dynamo (The azimuthal averaged velocity is subtracted in the movie). The diffusivity (scaled with the density) reflects the spiral structure and leads to interarm magntic fields. The non-axisymmetric velocity of the gas clouds responsible for the spiral structure gives magnetic fields within the optical arms. Both effects together show more or less magnetic fields within the arms. The dynamo with azimuthal averaged rotation and diffusivity is shown for comparison.
You can see the movies faster, if you copy the gif files to your computer and view them with xanim .
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