What sets the star-formation rate in the Milky Way? I. A multi-scale view of the star-formation rate

Abstract

Context. The star-formation rate (SFR) is one of the key quantities that characterizes the star formation process and has been extensively investigated both observationally and theoretically. Aims. We aim to provide a coherent multi-scale view of star formation by connecting Galactic-scale conditions (kpc) to the properties of individual star-forming clumps at sub-parsec scales. Methods. We perform a set of numerical simulations with large-scale turbulent forcing designed to reproduce physical conditions typical of the solar neighbourhood. Using adaptive zooming down to 0.03 pc, we obtain a population of star-forming clumps that is analyzed and compared with observational catalogues in a companion paper. Results. For column densities and velocity dispersions consistent with Galactic values, the resulting SFR is close to the rate inferred for the Milky Way. Comparing this value with the SFR expected from pure free-fall collapse shows that turbulence provides multiscale support that lowers the SFR by more than an order of magnitude. Additional regulation by stellar feedback, including ionizing radiation and protostellar outflows, likely reduces the SFR by an additional factor of 3-10. Comparisons with observations across multiple spatial scales show good overall agreement with this model. Conclusions. These results support a picture in which turbulence plays a central role in regulating star formation in the Milky Way. In combination with stellar feedback, it limits the star formation efficiency to only a few percent. Key words. stars: formation – ISM: clouds – physical processes: turbulence