  Star formation, together with the associated chemical and energy feedback, is
one of the most important processes in galaxy evolution. The star formation
activity in galaxies defines and affects many of their fundamental properties,
such as stellar mass, morphology and chemical enrichment levels. Simple models
for star formation in cosmological hydrodynamical simulations have shown to be
successful in reproducing the star formation rate (SFR) levels and shapes of
different types of galaxies. However, with the advent of high-resolution
simulations and more detailed observations, more sophisticated star formation
models are needed; in particular, to better understand the relation between
star formation and the amount of gas in the atomic and molecular phases. In
this work, we apply a novel star formation model, recently developed to work in
the context of hydrodynamical simulations, to the study of the SFR in Milky
Way-mass galaxies. The new implementation describes the formation of molecular
hydrogen from atomic material, considering also possible dependencies with the
chemical abundance of the gas. This allows to implement various star formation
models, where the SFR of a gas cloud is determined by the atomic and/or
molecular gas phases, and to compare their predictions to recent observational
results.
