Left: FTS and WILMA spectra of ¹²CO(3−2) in 4C 12.50, binned into 62  km s^-1 channels and shifted by a constant c₀, when needed. Right: flux-calibrated line profile of ¹²CO(3−2) , averaged over the WILMA and the FTS data to be least affected by potential artifacts. Gaussian functions with parameters that most closely fit the emission component at the systemic velocity and the absorption component at −950 km s^-1 are shown in blue and cyan, respectively. The inverse  H i absorption that is seen in the radio data of 4C 12.50 (Morganti et al. 2004) is overplotted in orange for an arbitrary scale and continuum level.