Top panel: IRAS F00188-0856 nuclear spectrum (black curve), extracted from a circular aperture with r < 0.4″. The corresponding pPXF best-fit model profile is shown in orange. The continuum-subtracted spectrum (blue curve) is obtained by subtracting the best-fit pPXF model from the original spectrum. The vertical blue lines mark the wavelengths of the emission lines detected in the spectrum; the vertical green lines mark the position of stellar absorption systems (i.e. from left to right: MgI triplet, Na ID and KI doublets). The regions excluded from the pPXF fit and corresponding to the most intense sky line residuals are highlighted as orange shaded areas; the portions of the spectra around 5300 Å are missing because a filter blocked the laser contamination. The inset in the top panel shows the red stellar continuum emission map in the vicinity of the nuclear regions, with HST/F160W contours as in Fig. C.1; the nuclear position is shown with a black marker. Bottom insets: multi-component best-fit analysis results for the main emission (Hβ and [O III], left; Hα, [N II] and [S II], right) and absorption (Na ID, centre) line features. Na ID multi-component best-fit curves are superimposed on the observed spectrum (black curve); emission components are not required to reproduce the total profile of Na ID.