Constraining the statistics of population III binaries

Abstract

We perform a cosmological simulation in order to model the growth and evolution of Population III (Pop III) stellar systems in a range of host minihalo environments. A Pop III multiple system forms in each of the 10 minihaloes, and the overall mass function is top-heavy compared to the currently observed initial mass function in the Milky Way. Using a sink particle to represent each growing protostar, we examine the binary characteristics of the multiple systems, resolving orbits on scales as small as 20 au. We find a binary fraction of ~35 per cent, with semi-major axes as large as 3000 au. The distribution of orbital periods is slightly peaked at ≲ 900 yr, while the distribution of mass ratios is relatively flat. Of all sink particles formed within the 10 minihaloes, ~50 per cent are lost to mergers with larger sinks, and ~50 per cent of the remaining sinks are ejected from their star-forming discs. The large binary fraction may have important implications for Pop III evolution and nucleosynthesis, as well as the final fate of the first stars. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.