Simulating Star Formation and Feedback in Galactic Disk Models

We use a high-resolution grid-based hydrodynamics method to simulate the multiphase interstellar medium (ISM) in a quiescent Milky Way-sized disk galaxy. The models are global and three-dimensional, and they include a treatment of star formation and feedback. We examine the formation of gravitational instabilities and show that a form of the Toomre instability criterion can successfully predict where star formation will occur. Two common prescriptions for star formation are investigated. The first is based on cosmological simulations and has a relatively low threshold for star formation but also enforces a comparatively low efficiency. The second only permits star formation above a number density of 10³ cm^-3 but adopts a high efficiency. We show that both methods can reproduce the observed slope of the relationship between star formation and gas surface density (although at too high a rate for our adopted parameters). A run that includes feedback from Type II supernovae is successful at driving gas out of the plane, most of which falls back onto the disk. This feedback also substantially reduces the star formation rate. Finally, we examine the density and pressure distribution of the ISM and show that there is a rough pressure equilibrium in the disk, but with a wide range of pressures at a given location (and even wider for the case including feedback).