Abstract:
The star formation rate is a very fundamental quantity that deeply influences the evolution of the Universe and which is only partly understood. In particular, its value in the Milky Way appears to be nearly two orders of magnitude lower than a simple estimate based on the freefall time, indicating that efficient supports are operating against gravity. Another remarkable relation is the so-called Schmidt-Kenicutt law which expresses the star formation rate as a function of the column density. In which conditions these two features can be reproduced? What are the physical processes explaining these observations?
To answer these questions, I will present numerical simulations of self-regulated, stratified, star forming interstellar medium. I will show that stellar feedback plays a fundamental role to regulate star formation and can reproduce star formation rates compatible with the values observed in the Milky Way. However at larger column densities, the stellar feedback appears to be larger than the values inferred from the Schmidt-Kenicutt relations. I will propose that a large scale turbulent driving, possibly due to energy injected at the galactic scale, is required to bring the star formation rate to the observed values. Indeed, numerical simulations show that strong enough turbulence can very significantly reduce star formation. To understand exactly how this occurs, I will present an analytical model that relies on the turbulent support and show how turbulent support exactly operates. Comparisons with dedicated numerical simulations reveal good agreement with the predictions of the model.