R_Fe-log(FWHM_Hβ, br)−log(L_Hβ, br) plane. Specifically, he have log(FWHM_Hβ, br) versus log(L_Hβ, br) colour-coded by R_Fe. Objects marked with a circle represent R_Fe upper limits as defined in the text. The background 2D histogram is obtained by binning the control sample (with a minimum of 30 objects per bin); individual objects from JWST are colour-coded with the same scale in R_Fe. Due to the large number of upper limits in the low-luminosity region, we also include the values derived from the composite spectra as symbols with thicker black edges. The coloured rectangles mark the regions where the control samples were drawn. The black solid arrow marks the direction of the PCA, as described in Sect. 5.2. SBS_0335-052E (black thick edge pentagon) has been shifted for a tighter image layout.