Abstract

Population II (Pop II) stars formed a few hundred million years after the Big Bang were key drivers of cosmic reionization and building blocks of high-redshift galaxies. How and when these stars formed is a subject of ongoing research. We conduct cosmological radiation hydrodynamical simulations to investigate the formation of Pop II star clusters in dark matter halos forming at z = 10-25 in the aftermath of a pair instability supernova (PISN). Our simulations model the formation of Population III and Pop II stars in a self-consistent manner along with their radiative, chemical, and SN feedback in halos of 5 × 105-7 107 M o˙. We find that a PISN evacuates the gas from halos ≤3 106 M o˙ and thereafter shuts off in situ star formation for at least 30 Myr. Pop II stellar clusters of 923 M o˙ and 6800 M o˙ form in halos of 3.8 × 107 M o˙ and 9 107 M o˙, respectively. The mode of star formation is highly episodic and mainly regulated by Pop II SN feedback. The average star formation rates are 10-5-10-4 M o˙ yr-1, and the star formation efficiency is less than 1%.