Outflow mass divided by outflow radius (M_out/R_out) versus outflow velocity. The lightblue line is the best linear fit to the data (slope = 2.61 ± 0.25). The shaded area indicates the 1σ uncertainty with and without including the intrinsic scatter term (lighter and darker colour, respectively). The blue dashed line shows the predictions for a energy-driven outflow (α = −2) and the red dotted-dashed line for a momentum-driven outflow (α = −1). Symbols as in Fig. 17.