Baseline-subtracted line profiles towards the center of NGC 5128 (Centaurus A) obtained with the ground-based telescopes SEST, JCMT, and APEX (top two rows) and with the HIFI instrument on-board of the Herschel Space Observatory (bottom two rows). Vertical scale is in Kelvin, horizontal scale is V_LSR in   km   s^-1. Species, transition and telescope used are identified at the top left corner of each panel. The HIFI   ¹²CO results for the J = 8–7, J = 10–9, and J = 13–12 transitions are the averages of the profile towards the nucleus and the adjacent positions separated from that by 10′′. Note that the deep absorption apparent in the ¹³CO (1–0) profile is real; its depth to negative values reflects the weakness of the line emission relative to the (subtracted) continuum strength at the same frequency. For more details, see Sect. 2 and Tables 2 and 3.