Gini–M₂₀ relation for the less active field galaxies (grey dots and contours), massive field galaxies (black stars) and SMG sample (red circles), in the a) F200W and b) F444W bands as well as histograms showing the distribution of each parameter on each axis, with the low-mass field scaled down by a factor 10. The solid black line indicates the boundary line between mergers and non-mergers as defined in Lotz et al. (2008). Both SMGs and field galaxies scatter about the line in the F200W band whilst the majority lie in the non-merger region of the equivalent F444W plot. In panels c) and d) we show the distributions of $M_{20}^{\mathrm{F}444\mathrm{W}}$ − $M_{20}^{\mathrm{F}200\mathrm{W}}$ and RFF^F444W − RFF^F200W. For each distribution, we indicate the KS-statistic showing that the SMGs have a stronger variation in morphology with wavelength with higher RFF and M₂₀ values at 2 μm than 4 μm indicating more structure in the residuals and disturbed morphologies.