Comparison of the line properties of OH⁺ and CO(9-8) between the QSO sample of this work with other high-z QSOs (Stanley et al. 2021; Shao et al. 2022) and DSFGs (Berta et al. 2021; Riechers et al. 2021) from the literature. In all panels, we colour the sources from Riechers et al. (2021) with blue-shifted OH⁺ absorption in black and colour the rest of the sample in grey. Left: OH⁺ absorption FWHM vs. velocity w.r.t. the CO(9-8) emission. Middle: OH⁺ emission FWHM vs. velocity w.r.t. the CO(9-8) emission. Right: dust temperature vs. CO(9-8) emission FWHM (of only the broadest CO component in each literature source). FWHMs are derived by multiplying the velocity dispersions in Table 1 by a factor of .