Number of hard MBHBs (grey solid) and single MBHs (grey dashed) per deg² (dN(z)/dΩ, black) as a function of redshift. Different colors represent the same but when the population of MBHBs is divided by semi-major axis (a_BH). Each panel corresponds to binaries with different total masses: 10⁴ − 10⁵ M_⊙ (top), 10⁵ − 10⁶ M_⊙ (middle), and 10⁶ − 10⁷ M_⊙ (bottom). Overall, the figure shows that LISA MBHBs represent 0.1%−1% of the MBHs between 10⁴ and 10⁷ M_⊙.