The properties of the ISM in disc galaxies with stellar feedback

Abstract: We perform calculations of isolated disc galaxies to investigate how the properties of the ISM, the nature of molecular clouds, and the global star formation rate depend on the level of stellar feedback. We adopt a simple physical model, which includes a galactic potential, a standard cooling and heating prescription of the ISM, and self gravity of the gas. Stellar feedback is implemented by injecting energy into dense, gravitationally collapsing gas, but is independent of the Schmidt-Kennicutt relation. We obtain fractions of gas, and filling factors for different phases of the ISM in reasonable ageement with observations. Supernovae are found to be vital to reproduce the scale heights of the different components of the ISM, and velocity dispersions. The GMCs formed in the simulations display mass spectra similar to the observations, their normalisation dependent on the level of feedback. We find ~40 per cent of the clouds exhibit retrograde rotation, induced by cloud-cloud collisions. The star formation rates we obtain are in good agreement with the observed Schmidt-Kennicutt relation, and are not strongly dependent on the star formation efficiency we assume, being largely self regulated by the feedback. We also investigate the effect of spiral structure by comparing calculations with and without the spiral component of the potential. The main difference with a spiral potential is that more massive GMCs are able to accumulate in the spiral arms. Thus we are able to reproduce massive GMCs, and the spurs seen in many grand design galaxies, even with stellar feedback. The presence of the spiral potential does not have an explicit effect on the star formation rate, but can increase the star formation rate indirectly by enabling the formation of long-lived, strongly bound clouds.