Optical images and IRAM-30 m spectra of the four sources in our sample with multiple pointings. In the images, north is up, east is left, while the crosses in magenta (+) and black/white (×) correspond to the central and offset pointings, respectively. The circles correspond to the CO(2  →  1) beams of 10.5″ each, with the exception of NGC 5985, for which the CO(1  →  0) beams of 21″ each are instead reported. The reported spectra are baseline-subtracted, and the x- and y-axes show the relative velocity and T_mb (in mK), respectively. The solid lines in the spectra are the Gaussian fits to the CO(1  →  0) and CO(2  →  1) lines.