1D profiles of log(n_e) along the flow in discrete velocity intervals (see Fig. 10). Error bars (smaller than the symbol size where the signal is strong) are determined a posteriori by conducting the analysis with input values of the line ratios and their uncertainties (evaluated from the 3σ error on the fluxes). Empty symbols indicate positions where n_e is above the high density limit of the [S ii] diagnostics, and the derivation has been made through the modified BE-technique described in Sect. 2.2.