Cross-correlation between spectral index measurements displayed in Fig. 5c (y-axis) and ratio of the flux density from ‘pure’ dust emission over the bsens 1.3 mm flux density at 3 mm angular resolution for each core from the getsf filtered catalogue (x-axis). The x-axis shows the percentage of 1.3 mm emission due to dust emission at 3 mm angular resolution. Free-free contaminated cores are shown in dark green, freefree dominated cores in light green, and ‘uncertain’ ones (see Sec. 4.2) in neutral green, and the rest of the cores are shown in black.