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Formation of the First Low-Mass Stars from Cosmological Initial Conditions

We simulate the formation of a metal-poor (10^-2 Zsun) stellar cluster in one of the first galaxies to form in the early Universe, specifically a high-redshift atomic cooling halo (z~14). This is the first calculation that resolves the formation of individual metal-enriched stars in simulations starting from realistic cosmological initial conditions. We follow the evolution of a single dense clump among several in the parent halo. The clump forms a cluster of ~40 stars and sub-stellar objects within 7000 years and could continue forming stars ~5 times longer. Protostellar dust heating has a negligible effect on the star formation efficiency, at least during the early evolutionary stages, but it moderately suppresses gaseous fragmentation and brown dwarf formation. We observe fragmentation in thin gaseous filaments and sustained accretion in larger, rotating structures as well as ejections by binary interactions. The stellar initial mass function above 0.1 Msun, evaluated after ~10^4 years of fragmentation and accretion, seems in agreement with the recent measurement in ultra-faint dwarf spheroidal Galactic satellites of Geha et al. (2013).