Abstract: The saying `Don't sweat the petty things and don't pet the sweaty things' may be an appropriate epitaph for a stress-free life, but can we also apply it to disc galaxies? The problem simulators have hangs on the complexity of the interstellar medium; a turbulent gas influenced by many forces that compete during star formation. The difficulty in modelling this has previously left simulators with a choice; put in all the physics to fully model the ISM, but restrict the box-size to only a small fraction of the galaxy, or model the entire galaxy but simplify the ISM to a fixed one-, two- or three-phase medium. At first glance, this would suggest global models are poor approximation to the real thing, but intriguingly star formation is observed to follow simple relations when considered on the global scale, hints that at this level the detail of the ISM is not important.
Recently, increases in computer power and improved techniques have begun to allow the creation of models of entire galaxy discs with a multiphase medium. This allows for the first time studies of how the ISM affects the galaxy on a global scale and allows us to ask the question; how important is the small scale when we consider the very large? In this work, I present global disc simulations with three different types of ISM and look at how their evolution differs.