Detector-frame distribution of metallicities of BH–BH, BH–NS, and NS–NS merger progenitors. More than 90% of BH–BH merger detections in all our models are systems formed with metallicites lower than 10% of the solar metallicity, i.e. Z < 0.1 Z_⊙. Such a strong dependence of compact binary merger formation with metallicity (see also Fig. 6), especially in the case of BH–BH systems, indicates the significance of SFRs at different metallicites across the Universe for the compact binary merger rates (see discussion in Sect. 6.3).