CO ladder in all four galaxies in H-ATLAS J084933.4+021443: W (red), T (blue), M (green), and C (yellow). The x axis is labelled with the rotational quantum number of the upper state (top; 1, 3, 4, and 7) and the rest frequency of the line (bottom). Small displacements in the x axis are used for the different galaxies to avoid confusion, and vertical lines demarcate the true x positions of the points. The y axis shows the line flux normalised to that of CO J:1–0. Line fluxes from this work are shown with solid circles and those from I13 are shown with circles. The dashed line shows the CO ladder expectation for the case of a constant brightness temperature on the Rayleigh-Jeans (RJ) scale, i.e. S ∼ ν² (note that the RJ approximation is not valid for high J).