Free-free emission at 32.9 GHz as a function of the SED temperature for each source. The shaded grey area corresponds to the range of temperature for which the β values derived are authorised. For each source the minimum and maximum values of the free-free emission percentage derived over the full temperature range are indicated at the top right of the plots. For single systems, the bolometric temperature, T_bol, derived from Herschel (Furlan et al. 2016) is indicated by a blue dashed line and the radiative temperature, T_rad, by a red dashed area or by a red dashed line in the case of FIR2.