Contributed Talk - Splinter Magnetic

Thursday, 24 September 2020, 12:38   (virtual room H)

How to launch galactic outflows with magnetic fields

Ulrich P. Steinwandel, Klaus Dolag, Harald Lesch and Andreas Burkert

We show that magnetic fields can launch outflows in galaxies that show non-axis symmetric instabilities like a bar via a fast-track radial inflow dynamo that can increase the galactic magnetic field strength at equipartition by a factor of 10-100. In two subsequent publications (Steinwandel et al. 2019 and Steinwandel et al. 2020a) we used high resolution numerical simulations of Milky Way-like galaxies to show that equipartition field strength of a few µG can be established on Myr time-scales by the small-scale turbulent dynamo which we could quantify over the Kazantsev power-spectrum and the correlation between the magnetic field strength and the field line curvature. We were then able to show that this dynamo process is switched of when it saturates with the turbulent kinetic energy (on the smallest scales) and that the large-scale dynamo is ordering the field on larger scales to an observed quadrupolar field strength. In Steinwandel et al. (2020a) we investigated how magnetic fields can drive outflows in galaxies in numerical simulations. We will present an analytical prescription of a fast-growing dynamo that is initialized by a bar-formation process, informed by out numerical simulations. This outflow process has the potential to explain the large observed fraction of galaxies that show signs of strong magnetic fields and are known to have bars at redshift zero. Furthermore, we extended the analytic model to higher redshift, where we could derive star formation rates, outflow rates and mass loading factors in exceptionally good agreement with results from KMOS3D (Förster-Schreiber 2019). Specifically, the low obtained mass loading factors of our model in combination with the structural shape of the line-of-sight velocity profiles obtained from our numerical simulations, indicates that this process potentially plays a major role in explaining high redshift outflows.