Comparison between (i) the K-S relation plot derived for all sample galaxies and taking all the ¹²CO emission lines at the common resolution of 200 pc into account, as shown in Fig. 7; and (ii) results from Bigiel et al. (2008). The model predictions from Krumholz et al. (2009) are also shown with solar metallicity and clumping factor c = 1, 2, and 5; see Krumholz et al. (2009) for more details. Also shown (as a blue short-dashed line) is the trend for star-forming galaxies and mergers found by Genzel et al. (2010) using a common conversion factor α_CO (=3.2 M_⊙ pc^-2 (K km s^-1)^-1). The horizontal axis has been adjusted to our α_CO (=3.5 M_⊙ pc^-2 (K km s^-1)^-1) and our non-inclusion of helium. We have also plotted the merger/starburst trend by Genzel et al. (2010) (with α_CO = 1 M_⊙ pc^-2 (K km s^-1)^-1) as shown by a (red) long-dashed line.