NMF-learned basis vectors. Panel a shows the basis vectors obtained from a sequential rank–10 NMF decomposition applied to 80% of the sample. The index n labels each basis vector. The names and rest-frame wavelengths of prominent spectral emission and absorption lines are indicated in the upper panels. Panel b presents zoomed-in views of the [O II] and Lyα emission lines, shown in the first and second columns, respectively. In each zoom-in, the line’s peak flux is normalized to one, the line rest wavelength is shown with a vertical dashed gray line, and the corresponding basis vector is indicated.