Continuum-subtracted IRAM PdBI spectra of the CO(1 − 0) and CO(2 − 1) emission lines. These spectra are extracted from circular apertures with diameters of 6 arcsec. Top panels: full flux scale. Bottom panels: expanded flux scale to highlight the broad components. The two emission lines were simultaneously fitted with four Gaussian functions (red profiles, see text) tied to have the same centers and widths for the two transitions, to reproduce the three main components of each line (i.e. core, blue, and red broad components). The blue contours represent the results of the fit.