Central panels: Na ID absorption (Abs.) and emission (Em.) line fluxes across the FOV obtained by integrating for each spaxel the spectra in the regions 5860 − 5910 Å and 5890 − 5920 Å, respectively. Negative and positive fluxes were obtained after subtracting the stellar contribution (pPXF best fit); for the absorption fluxes, we also removed the He I emission line (simultaneous best-fit results). Insets: different spectra extracted from the regions labelled in the flux maps, with normalised fluxes: absorption- (emission-) dominated Na ID line profiles are shown in the right (left) panels. Red curves represent the Na ID stellar contribution fitted with pPXF, rescaled for visual purposes. Vertical dashed lines indicate the (NW nucleus systemic) wavelengths of the He I and Na ID doublet lines.