Magnetic buoyancy in simulated galactic discs with a realistic circumgalactic medium

We present simulations of isolated disc galaxies in a realistic environment performed with the Tree-SPMHD-Code GADGET-3. Our simulations include a spherical circumgalactic medium (CGM) surrounding the galactic disc, motivated by observations and the results of cosmological simulations. We present three galactic models with different halo masses between 10^{10} and 10^{12} M_⊙, and for each we use two different approaches to seed the magnetic field as well as a control simulation without a magnetic field. We find that the amplification of the magnetic field in the centre of the disc leads to a biconical magnetic outflow of gas that magnetizes the CGM. This biconical magnetic outflow reduces the star formation rate (SFR) of the galaxy by roughly 40 {{ per cent}} compared to the simulations without magnetic fields. As the key aspect of our simulations, we find that small-scale turbulent motion of the gas in the disc leads to the amplification of the magnetic field up to tens of μ G, as long as the magnetic field strength is low. For stronger magnetic fields, turbulent motion does not lead to significant amplification but is replaced by an α-ω dynamo. The occurrence of a small-scale turbulent dynamo becomes apparent through the magnetic power spectrum and analysis of the field lines' curvature. In accordance with recent observations, we find an anticorrelation between the spiral structure in the gas density and in the magnetic field due to a diffusion term added to the induction equation.