Top left: E(B − V)_gas as a function of the Na ID EW. The dashed line represents Eq. (4), derived under the assumption that both quantities are proportional to the hydrogen column density N_H. Top right: covering factor vs. optical depth for each kinematic component used to model the Na ID profiles. The points in the top panels are colour-coded according to their position in the [N II]-BPT diagram (Fig. 14, top right). Bottom left: covering factor map, obtained from the total Na ID profiles following the Rupke et al. (2005a) prescription. Bottom right: column density map, obtained by summing the N_H derived from each kinematic component required to model Na ID profiles.