Radial flux density profiles for the starless core models described in Sect. 5.1 (upper row) and for B68 and FeSt 1-457 (lower row, see Sect. 5.2). The observing frequency is shown in black at the top of each column, while numbers in the upper-right corner of each subplot represent the radius-averaged S/N for the two values of κ (0.5 and 0.7 for models A, B, C and B68, and 0.68 and 0.88 for FeSt 1-457, see Eq. (9)). Shaded areas encompass the curves obtained with Eq. (9) by using the two values of κ (see Fig. 2 for colour-coding). The telescope beam is shown in the leftmost column for models A, B, and C (dotted black line, 300″), B68 (short-dashed black line, 330″), and FeSt 1-457 (long-dashed black line, 284″). Hatched areas display SKA sensitivities for one hour of integration at different frequencies. The two panels on the right side show the flux density as a function of frequency. Empty (solid) circles refer to a S/N smaller (larger) than 3, respectively. The spectral index α is shown on the right of each curve.