Left: integrated Hα flux map scaled to emphasize the clumpy structure of the inner filament. Centre left: Hα flux map after the clumps of the inner filament have been subtracted to show the structure of the arcs. Centre right: velocity structure of the Hα – [NII] complex. Right: FWHM of the Hα emission showing regions of increased line width surounding the clumps. The FWHM map shows that the linewidth is broadened at the edges of the clumps up to 400−600 km s^-1, suggesting that the gas here may be shocked.