Mass-radius plot; r_FWHM is the beam-corrected radius at FWHM level. The symbols are the same as in Fig. 3. The boundary for massive-star formation derived by Kauffmann & Pillai (2010) (M [M_⊙] = 870(r/pc)^1.33, rescaled to match our dust opacity is indicated as a dashed line. Sources above this line are able to form massive stars. The uncertainty in mass is shown for each point. A variation of a factor of 2 in mass (see text) is indicated in the bottom right corner.