How non-thermal pressure impacts the modelling of star formation in galaxy formation simulations: magnetic field effects

ABSTRACT In cosmological simulations of large-scale structure, star formation and feedback in galaxies are modelled by so-called subgrid models, which represent a physically motivated approximation of processes occurring below the resolution limit. However, when additional physical processes are considered in these simulations, for instance, magnetic fields or cosmic rays, they are often not consistently coupled within the descriptions of the underlying subgrid star formation models. Here, we present a careful study on how one of the most commonly used subgrid models for star formation in current large-scale cosmological simulations can be modified to self-consistently include the effects of non-thermal components (e.g. magnetic fields) within the fluid. We demonstrate that our new modelling approach, which includes the magnetic pressure as an additional regulation on star formation, can reproduce global properties of the magnetic field within galaxies in a set-up of an isolated Milky Way-like galaxy simulation, but is also successful in reproducing local properties such as the anticorrelation between the local magnetic field strength with the local star formation rate as observed in galaxies (i.e. NGC 1097). This reveals how crucial a consistent treatment of different physical processes is within cosmological simulations and gives guidance for future simulations.