CO LF across redshift bins: z = 0–0.5, z = 0.5–1, z = 1–2, z = 2–3, z = 3–4 and z = 4–6. Detections are shown in circles and non-detection as arrows. The vertical dotted line in each panel indicates the detection limit, representing the faintest luminosity detectable at a 50% reduction in primary beam sensitivity. The CO LFs are fitted using only the filled points that lie above this luminosity threshold. The best-fit Schechter function (Schechter 1976) is plotted, with Φ^* and L^′* allowed to vary freely, while the faint-end slope is fixed at α = −0.2. The shaded region represents 1σ confidence intervals. Overall, the CO LF reveals a decreasing normalisation factor, while the ‘knee’ of the function shifts to higher luminosities as redshift increases.