Left panel shows the explained variance ratio of the principal component analysis (PCA) decomposition. The six first components, which are enough to explain the whole data set, are plotted in the right panel. Components 0, 3 and 5 show no remarkable features in the Fe L2,3 ionization energy and seem rather related to the background of the spectra due to their power-law behaviour, while component 1 is almost constant and therefore could be related to the dark noise in the detector.