Left panel: maximum detectable angular size resulting from the combined effects of r.m.s sensitivity and total flux density selection limit for images with 0.″75 (grey line), 1.″2 (magenta line) and 1.″5 resolution (pink line). The maximum angular size is estimated from the ratio S_T/5σ using the geometric mean of the two limiting cases (see text). Right panel: redshift evolution of the median linear sizes of three different samples of SFGs: the blue points are the same as in Fig. 1 and correspond to radio sources with 3 GHz total flux density S_T >  20 μJy, while the purple squares and magenta triangles correspond to subsamples with S_T >  30 μJy and S_T >  40 μJy, respectively.