Impact of population III stars on the astrophysical gravitational-wave background

We probe the astrophysical gravitational-wave background resulting from compact binary coalescences, focusing on population III binary black holes. We exploit results of state-of-the-art simulations on the evolution of population I-II and III binaries, considering a variety of initial condition and star formation rate models for the latter. The contribution from population III binary black holes is found to be very small, with no effect on the gravitational-wave spectrum. A network of third-generation detectors will detect easier individual population III binaries, due to their significantly higher masses, hence decreasing even further their residual contribution.