Upper panel: model turbulent velocity dispersion as a function of star-formation surface density. The symbols are the same as in Fig. 10. In addition, filled triangles are the observed velocity dispersions from Downes & Solomon (1998). Filled circles are observed Hα velocity dispersions from Cresci et al. (2009). Lower panel: observed CO velocity dispersion (Tacconi et al. 2013) as a function of the model velocity dispersion. The symbols are the same as in Fig. 10. The solid line corresponds to equality and the dotted lines to factors of 1/1.5 and 1.5.