Example of the old stellar population modeling in a 200 × 200 pixels² box near the center of the galaxy. Top panel: Random spectra taken in the box to illustrate the strong brightness gradient. Bottom panel: Same spectra after a normalization by their mean flux. The resulting median spectrum of all the normalized spectra contained in the box is shown in blue, the smoothed version used as an estimation of the old stellar population is shown in red. The noise level of the individual 7 × 7 binned spectra used during the fitting procedure is shown as an orange envelope.