The [C i] spectra (broken lines) overlaid on the CO rotational transition used (full lines) for the published high redshift [C i] detections, where the [C i] intensity is scaled by the value shown in the legend. All spectra are shown at the original spectral resolution and have been re-sampled to the reference frequency of the CO transition (ν_ref in Table 1, thus showing the offset from this), except in the case of SMM J213511–0102 (the subject of a spectral scan), where both spectra are shown relative to the derived CO 1 → 0 redshift of z = 2.32591 (Danielson et al. 2011). Note that, for the sake of clarity, the spectra for MM 18423+5938 have been truncated from the full  ± 2400 km  s^-1 range (Lestrade et al. 2010).