CO J = 1 → 0 spectra from NGC 253 (lower panel) and Mrk 231 (upper panel) on a LSR V_LSR = 0 km s^-1 frequency scale. The spectra were smoothed to channel spacings of ~8.52 and 10.84 km s^-1 (3.125 and 4.0 MHz), respectively. The frequency range of the upper panel is wider to show the molecular outflow at the foot of the main spectral component, seen in CO and other species (e.g., Feruglio et al. 2010; Aalto et al. 2012).