  In cosmological simulations of large-scale structure star formation and
feedback in galaxies are modelled by so-called sub-grid models, that 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 sub-grid
star formation models. Here, we present a careful study on how one of the most
commonly used sub-grid 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, that includes the magnetic
pressure as an additional regulation on star formation, can reproduce global
properties of the magnetic field within galaxies in a setup of an isolated
Milky Way-like galaxy simulation, but is also successful in reproducing local
properties such as the anti-correlation 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.
