Modelling entire disc galaxies is a difficult task for the most advanced
computer system, resulting in the small scale physics of the interstellar
medium being simplified, often to a single phase (or fixed two or three
phase) gas. Simulations of local patches, however, reveal a complex ISM; a
turbulent mix where many forces compete during star formation. This
suggests global models are likely to be a poor approximation to the real
thing and that we may be missing important clues in their evolution and
star formation histories. That said, observations show simple relations
between global star formation and gas density, indicating the opposite is
true and the detail of the ISM is not important. So can we ignore the fine
structure on large scales and if so why?
In this work, I present some of the first global
models that develop a multiphase ISM, comparing isothermal systems with
galaxies that contain feedback and background heating to try and uncover
the most important parameters in star formation in disc galaxies.