Formation of Population II Star Clusters in the Aftermath of a Pair Instability Supernova

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⊙. We find that a PISN evacuates the gas from halos ≤3 × 106 M⊙ and thereafter shuts off in situ star formation for at least 30 Myr. Pop II stellar clusters of 923 M⊙ and 6800 M⊙ form in halos of 3.8 × 107 M⊙ and 9 × 107 M⊙, 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⊙ yr−1, and the star formation efficiency is less than 1%.