2D velocity channel maps of the logarithm of the electron density (left), of the ionisation fraction (centre) and of the logarithm of the total density (right). Greyscales are linear. Low velocity interval (LVI) is defined as −120 to +25 km s^-1, medium velocity interval (MVI) is defined as −270 to −120 km s^-1 and high velocity interval (HVI) is defined as −420 to −270 km s^-1. Contours: cyan – [S ii]λ6716 at 3σ; orange – [S ii]λ6731 at 3σ; green – region above [S ii] critical density; blue – [O i]λ6363 at 3σ; red – [N ii]λ6583 at 3σ.