Portion of the outflow-integrated spectra of Mkn 848 around the He I and Na ID lines for the NW (left panel) and SE (right panel) regions. The spectra are extracted from the spaxels associated with high-velocity gas in the neutral phase, with ΔV₀₂ <  −900 km s⁻¹, for the NW system, and ΔV₀₂ <  −750 km s⁻¹ for the SE system. The two spectra have a normalised continuum, and the superimposed best-fitting Na ID components in absorption are obtained following Rupke et al. (2005a), assuming a geometrical configuration with partially overlapping sodium atoms (Sect. 6). The He I emission line is instead fitted with a Gaussian profile.