Star Cluster Formation in Cosmological Simulations. II. Effects of Star Formation Efficiency and Stellar Feedback

Abstract

Abstract The implementation of star formation and stellar feedback in cosmological simulations plays a critical role in shaping galaxy properties. In the first paper of the series, we presented a new method to model star formation as a collection of star clusters. In this paper, we improve the algorithm by eliminating accretion gaps, boosting momentum feedback, and introducing a subgrid initial bound fraction, f i , that distinguishes cluster mass from stellar particle mass. We perform a suite of simulations with different star formation efficiency per freefall time and supernova momentum feedback intensity . We find that the star formation history of a Milky Way–sized galaxy is sensitive to , which allows us to constrain its value, , in the current simulation setup. Changing from a few percent to 200% has little effect on global galaxy properties. However, on smaller scales, the properties of star clusters are very sensitive to . We find that f i increases with and cluster mass. Through the dependence on f i , the shape of the cluster initial mass function varies strongly with . The fraction of clustered star formation and maximum cluster mass increase with the star formation rate surface density, with the normalization of both relations dependent on . The cluster formation timescale systematically decreases with increasing . Local variations in the gas accretion history lead to a 0.25 dex scatter for the integral cluster formation efficiency. Joint constraints from all the observables prefer the runs that produce a median integral efficiency of 16%.