On the Relationship Between Star Formation and the Interstellar Medium in Numerical Simulations

Abstract

The cycle of star formation is the key to galaxy evolution. Stars form in massive collections of extremely dense cold gas. Stellar feedback will inject turbulence into the interstellar medium (ISM) and regulate the availability of more star-forming gas. This gas is an integral component in the cycle of star formation but is very difficult to model in numerical simulations. We have investigated the interplay between star formation and the structure of the ISM in numerical simulations. These simulations were done using the Smoothed Particle Hydrodynamics code Gasoline. For this work we introduce a new treatment for photoelectric heating in Gasoline. We first explore the impact of numerical parameter choices for the star formation threshold density, star formation efficiency and feedback efficiency. Of these three parameters, only the feedback efficiency plays a large role in determining the global star formation rate of the galaxy. Further, we explore the truncation of star formation in the outer regions of galactic discs and its relation to the presence of a two-phase thermal instability. In the outer regions of the simulated discs, gas exists almost exclusively in one warm phase, unsuitable to host large-scale star formation. We find that the disappearance of two-phase structure in the ISM corresponds to the truncation of star formation.