Colour-composite image of the Hα (red), [OI] (green), and [OIII] (blue) emission from channel 15. The star-forming clump can be seen to the south-west end of the filament as a red region, which indicates that it is dominated by Hα emission. The other clumps appear blue because they are very bright in [OIII] emission. Finally, the arcs appear green because they are stronger in [OI] relative to the other emission lines than the clumps.

Fitted flux in each of our primary diagnostic lines. The key line ratios, average velocity, and the full width at half maximum for all of the lines are shown.

Hα channel maps. The channels cover the velocity range of −330 km s^-1 to 300 km s^-1 relative to the mean redshift of the filament (z = 0.00108, shifted by ~ –220 km s^-1 relative to the central galaxy) with channels of 30 km s^-1. Flux units are 10^-20 erg s^-1 cm^-2 Å^-1.

[NII] channel maps. The channels cover the velocity range of −330 km s^-1 to 300 km s^-1 relative to the mean redshift of the filament (z = 0.00108, shifted by ~-220 km s^-1 relative to the central galaxy) with channels of 30 km s^-1. Flux units are 10^-20 erg s^-1 cm^-2 Å^-1.

Hβ channel maps. The channels cover the velocity range of −330 km s^-1 to 300 km s^-1 relative to the mean redshift of the filament (z = 0.00108, shifted by ~ –220 km s^-1 relative to the central galaxy) with channels of 30 km s^-1. Flux units are 10^-20 erg s^-1 cm^-2 Å^-1.

[OIII] channel maps. The channels cover the velocity range of −330 km s^-1 to 300 km s^-1 relative to the mean redshift of the filament (z = 0.00108, shifted by ~ –220 km s^-1 relative to the central galaxy) with channels of 30 km s^-1. Flux units are 10^-20 erg s^-1 cm^-2 Å^-1.

[SII] channel maps. The channels cover the velocity range of −330 km s^-1 to 300 km s^-1 relative to the mean redshift of the filament (z = 0.00108, shifted by ~ –220 km s^-1 relative to the central galaxy) with channels of 30 km s^-1. Flux units are 10^-20 erg s^-1 cm^-2 Å^-1.

[OI] channel maps. The channels cover the velocity range of −330 km s^-1 to 300 km s^-1 relative to the mean redshift of the filament (z = 0.00108, shifted by ~ –220 km s^-1 relative to the central galaxy) with channels of 30 km s^-1. Flux units are 10^-20 erg s^-1 cm^-2 Å^-1. The first 7 channels are covered by a skyline and as such are extremely noisy, therefore no emission is visible. We have retained their panels, but set their value to zero so that the channels are consistent in velocity with the other channel maps.

Example spectrum taken from one of the clumps. Plots 1 and 2 show spectra taken from just inside one of the clumps, where the FWHM map shows that the lines are narrow, but are located near to the broad region seen at the edge of the clumps. Plots 3 and 4 are spectra taken from the centre of one of the clumps and the broad boundary region seen in the FWHM map. Note that plots 1 and 2 show a narrow line dominating the profile with a FWHM similar to that seen from the centre of the clumps (plot 3), but the line broadens significantly at a flux lower than ~30 erg cm^-2 s^-1 Å^-1. This broad base is more consistent with the FWHM of the boundary region (plot 4). The red line in plots 1 and 2 shows the best-fit single-component model (plot 1) and the best-fit model with a second broad component added at the same velocity (plot 2). The two-component model clearly provides a better fit to the line, suggesting that the broad emission from the edge of the clumps is present here, but is much less significant than the narrow-line emission from the clump. We interpret this as evidence of a shocked shell of gas surrounding a much greater mass of unshocked gas within the centre of the clumps.