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

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 × 10 5 –7 × 10 7 M ⊙ . We find that a PISN evacuates the gas from halos ≤3 × 10 6 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 × 10 7 M ⊙ and 9 × 10 7 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%.