Same profile for [O III]λλ4959,5007 as in Fig. 16 (blue), together with the [O III]λλ4959,5007 profile for the full 13″ × 13″ field as observed by Sandin et al. (2013). The slit 1 profile was multiplied by a factor of 7.2 to match the integrated emission at ≥ − 750 km s⁻¹. We note strong [O III] emission for ≤ − 750 km s⁻¹ for the larger field-of-view compared to the slit 1 observations. This emission corresponds to about 10% of the total [O III] emission. A minor fraction (∼10%) of the emission at ≤ − 750 km s⁻¹ could be due to [Fe III] λ4986, as displayed in Fig. 17, but most of it comes from the approaching “wall” described in Sect. 3.2.