A new star formation recipe for magneto-hydrodynamics simulations of galaxy formation

Abstract

Star formation has been observed to occur at globally low yet locally varying efficiencies. As such, accurate capture of star formation in numerical simulations requires mechanisms that can replicate both its smaller-scale variations and larger-scale properties. Magnetic fields are thought to play an essential role within the turbulent interstellar medium (ISM) and affect molecular cloud collapse. However, it remains to be fully explored how a magnetised model of star formation might influence galaxy evolution. We present a new model for a sub-grid star formation recipe that depends on the magnetic field. We run isolated disk galaxy simulations to assess its impact on the regulation of star formation using the code RAMSES. Building upon existing numerical methods, our model derives the star formation efficiency from local properties of the sub-grid magnetised ISM turbulence, assuming a constant Alfvén speed at sub-parsec scales. Compared to its non-magnetised counterpart, our star formation model suppresses the initial starburst by a factor of two, while regulating star formation later on to a nearly constant rate of $\sim 1~M_{\odot}~\mathrm{yr}^{-1}$. Differences also arise in the local Schmidt law with a shallower power law index for the magnetised star formation model. Our results encourage further examination into the notion that magnetic fields are likely to play a non-trivial role in our understanding of star and galaxy formation.