Contribution to the total CO APS at z = 5.2 of each stellar mass bin and CO transition. The left axis and the dotted black curve show the cumulative number count of CO emitters per bin of stellar mass (in percent) redshifted in the frequency channel 305 ± 0.5 GHz (z_[CII] = 5.2). The right axis shows the cumulative contribution (in percent) to the total CO power amplitude. Coloured curves correspond to each CO transition, and the red curve corresponds to the sum of all CO transitions. The 90% stellar mass completeness in COSMOS2015 for each CO line is indicated with the same colour code on the x-axis. For comparison, the [C_II] level (in percent) is represented with the dashed green line. Power amplitudes are averaged for 0.12 < k < 0.24 arcmin⁻¹.