Spectra of HN¹³C(1–0) obtained for the sources classified as HMSCs (first column), HMPOs (second column), and UC HII regions (third column). For each spectrum the x-axis represents a velocity interval of ± 20 km s^-1 around the systemic velocity listed in Table 1 of Fontani et al. (2015b). The y-axis shows the intensity in main-beam temperature units. The red curves are the best Gaussian fits obtained with CLASS. For some sources (I20293-WC, G034-G2, G034-F2, G5.89-0.39, G034-F1, G028-C1, and I23385), we have observed two components: we have fitted both lines and used only the line centered on the systemic velocity of the source to compute the column densities.