Global dynamics of the interstellar medium in magnetised disc galaxies
  Magnetic fields are an elemental part of the interstellar medium in galaxies.
However, their impact on gas dynamics and star formation in galaxies remains
controversial. We use a suite of global magnetohydrodynamical simulations of
isolated disc galaxies to study the influence of magnetic fields on the diffuse
and dense gas in the discs. We find that the magnetic field acts in multiple
ways. Stronger magnetised discs fragment earlier due to the shorter growth time
of the Parker instability. Due to the Parker instability in the magnetised
discs we also find cold ($T<50\,\mathrm{K}$) and dense
($n\sim10^3-10^4\,\mathrm{cm}^{-3}$) gas several hundred pc above/below the
midplane without any form of stellar feedback. In addition, magnetic fields
change the fragmentation pattern. While in the hydrodynamical case, the disc
breaks up into ring-like structures, magnetised discs show the formation of
filamentary entities that extent both in the azimuthal and radial direction.
These kpc scale filaments become magnetically (super-)critical very quickly and
allow for the rapid formation of massive giant molecular clouds. Our
simulations suggest that major differences in the behaviour of star formation -
due to a varying magnetisation - in galaxies could arise.
