Constraining the statistics of Population III binaries

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 similar to 35 per cent, with semi-major axes as large as 3000 au. The distribution of orbital periods is slightly peaked at less than or similar to 900 yr, while the distribution of mass ratios is relatively flat. Of all sink particles formed within the 10 minihaloes, similar to 50 per cent are lost to mergers with larger sinks, and similar to 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.