Mass distribution constraint. In each panel, filled contours show the 90% and 50% credible regions of the probability distribution P(m | θ_m) from which both M₁ and M₂ are sampled, while the thick solid line shows the median distribution at each m. The d_j, GW constraint is used. Grey dashed lines show the edges of the corresponding 90% and 50% credible regions when using only the priors. Left-hand panel: the result for the power law mass distribution model, the central panel shows that for the Gaussian model, and the right-hand panel compares the two results with a log-scale vertical axis, to emphasise the lower 90% contour.