Distributions of the donor (left column) and compact object (NS or BH; right column) masses at the onset of the XRB phase in the three models described in Sect. 6.1. The darker colors on each panel correspond to the distributions of masses of XRBs that become merging DCOs generated in ten runs for each model, as is described in Sect. 7.3. It means that the distributions for merging DCO progenitors are ten times overestimated with respect to the distributions of the other XRBs in the figure to show which part of the parameter space they occupy.