Distribution of the major axis FWHM sizes of our COSMOS SMGs as seen at ν_obs = 3 GHz is shown by an open histogram. For comparison, the following SMG major axis size distributions are also shown: 1.4 GHz sizes from Biggs & Ivison (2008), 1.1 mm sizes from Ikarashi et al. (2015), and the extent of CO molecular gas in the SMGs studied by Tacconi et al. (2006). The upper size limits were placed in the bins corresponding to those values. The vertical dashed lines show the corresponding median major axis sizes (4.2 kpc for AzTEC1–21a, 6.3 kpc for the Biggs & Ivison (2008) SMGs, 1.6 kpc for the Ikarashi et al. (2015) SMGs, and 4.1 kpc for the CO sizes from Tacconi et al. (2006); survival analysis was used to take the upper size limits into account when calculating the median sizes). See text for details.