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tokens: all models and for both metallicity evolution scenarios. This indicates that BH–BH mergers are expected to be dominant GW sources within the framework of the evolution adopted in models V1, V2, and V4. If no detections are made after a modest increase of LIGO/Virgo sensitivity, these specific evolutionary models will be eliminated in the context of BH–BH formation. Our calculations incorporate the evolution of average metallicity with redshift into the cosmological model of the universe; a broad spectrum of metallicities is employed in our population synthesis rate predictions. Changing the details of the adopted metallicity evolution model, within the uncertainties, produces at best modest effects on the rate predictions. Specifically, the low metallicity models produce somewhat higher merger rate densities for heavy mergers (BH–BH) and somewhat lower merger rate density for low-mass mergers (NS–NS). These trends are understood in terms of the effects of metallicity on the BH–BH formation (low metallicity boosts the formation) and on the NS–NS formation (low metallicity suppresses the formation; see Dominik et al. 2012 ). For example, the standard model (V2) merger rate density changes from for low metallicity evolution (see Table 3 and Figure 2 ) to for high metallicity evolution (see Table 4 and Figure 3 ) for BH–BH mergers with total mass 25–37 . The decrease of merger rate density from low to high metallicity evolution is rather moderate: only a factor of ∼2. Note that metallicity itself plays a crucial role in the formation process of BH–BH binaries (Belczynski et al. 2007 , 2010a ). For example, a group of stars with solar metallicity will form ∼10–100 times fewer BH–BH mergers than the same group with 10% solar metallicity (de Mink Belczynski 2015 ). However, once we incorporate this very strong dependence into cosmological models of the universe and employ a broad spectrum of metallicities (as in our methods II and III), the merger rate density predictions are not as strongly affected. Both metallicity evolution models generate (alas with a different efficiency) low metallicity stars (typical progenitors of BH–BH mergers). A broad BH–BH merger delay time distribution (Dominik et al. 2013 , 2015 ) allows for both models to produce BH–BH binaries that will merge at low redshifts. 5.2. Comparison of Models with Forecasted Advanced LIGO/Virgo Upper Limits In Figures 5 and 6 and Tables 5 and 6 we present evolutionary model predictions for double compact object merger rate densities. The predictions are constructed with method II (see Section 2.2 ) and contrasted with the forecasted advanced LIGO/Virgo upper limits (see Section 4.2 ). Our models are described in Section 3 . Figure 4. Merger rate density for BH–NS systems for our low metallicity evolution scenario predicted (with method II) for advanced LIGO/Virgo. Note that only the delayed SN explosion model (V4) and the optimistic model (V1) make detections likely, while the other models