Disc fragmentation and oligarchic growth of protostellar systems in low-metallicity gas clouds

ABSTRACT We study low-metallicity star formation with a set of high-resolution hydrodynamics simulations for various gas metallicities over wide range 0–$10^{-3} \ {\rm Z_{\bigodot }}$. Our follow non-equilibrium chemistry and radiative cooling by adopting realistic elemental abundance dust size distribution. examine the condition fragmentation collapsing clouds (cloud fragmentation; CF) accretion discs (disc DF). find that CF is suppressed due to rapid heating accompanied molecular hydrogen even efficient ${\gtrsim}10^{-5} Instead, DF occurs in almost all runs regardless metallicity. also that, discs, growth protostellar systems overall oligarchic. The primary protostar grows through gas, secondary protostars form interaction spiral arms or break-up rapidly rotating protostar. Despite vigorous fragmentation, large fraction are destroyed mergers tidal disruption events. For few hundred years after first adiabatic core formation, only several survive disc, total mass 0.52–$3.8 M_{\bigodot