SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation

Abstract Most stars are formed as star clusters in galaxies, which then disperse into galactic disks. Upcoming exascale supercomputational facilities will enable simulations of galaxies and their formation by resolving individual (star-by-star simulations). This substantially advance our understanding cluster formation, assembly histories galaxies. In previous galaxy simulations, a simple stellar population approximation was used. It is, however, difficult to improve the mass resolution with this approximation. Therefore, model for forming that can be used must established. first paper series from SIRIUS (SImulations Resolving IndividUal Stars) project, we demonstrate stochastic star-by-star simulations. An assumed initial function (IMF) is randomly assigned newly model. We introduce maximum search radius assemble surrounding gas particles form particles. study, perform N-body/smoothed particle hydrodynamics formations turbulent molecular clouds ultra-faint dwarf test cases. The IMF correctly sampled if larger than value estimated threshold density adopted. small clouds, massive highly because number stars. confirm efficiency do not strongly affect results. find naturally reproduce relationship between most total clusters. Herein, models applied varying wide range resolutions.