Example of this work’s emission line measurement process. The top panel shows the pPXF fit (blue) to the continuum shape of the stacked spectrum (red), with residuals shown in lime green. In the bottom panel, we zoom in to the regions with rest-frame wavelengths around the [O II]λ3727 (left) and Hβ (right) emission lines. In the panel the residual spectrum is shown in lime green; the magenta lines show our Gaussian fit to the emission lines, as indicated.