Orbital period versus mass ratio distribution of BH binaries with a noncompact companion (mainly main-sequence stars). The results shown are only for the SMT subchannel (i.e., they do not include the systems that evolved or would evolve through CE). With the black dots, we mark the progenitors of BH–BH mergers. In the top panel are the systems that become BH–BH merger progenitors once a specific angular momentum loss of the accretor is adopted. In the bottom panels, the black dots mark the systems that would become BH-BH progenitors under assumptions of high specific angular momentum loss, corresponding to the outer Lagrangian point. The left panels are for systems with Z = 1% Z_⊙; right panels are for those with Z = 10% Z_⊙. The results are for 100 000 generated binary systems with their initial masses in the range M₁ > 15 M_⊙ and M₂ > 5 M_⊙.