Lower panel: the CO J = 1–0 flux, in Jy km s^-1, measured in one beam at the galaxy center, versus the 250 μm flux in Jy in the same area for galaxies in the M- and S-sample. The filled squares (red in the online version) are for beams of 100 arcsec FWHM, while the filled triangles (blue) are for beams of 45–55 arcsec FWHM. Upper panel: same quantities as in the lower panel but integrated over the whole galaxy. Filled circles are for galaxies mapped in CO while open circles are for galaxies whose total integrated CO flux has been inferred using pointed observations (see text for details).