Power spectrum of the injected filament shown in Fig. 4 for different B₀ models, as labelled. The vertical cyan dotted lines show the integration scale limits used to compute P_S. They correspond respectively to about half the largest scale in the image k⁻¹ = 2173″ ∼ 483 pixels and k⁻¹ = 40″ (corresponding to twice the synthesised beam full width at half maximum scale). The black lines show P(k) resulting from the source injection into uvw visibilities, whereas the grey lines show the result from the image-plane addition of the simulated image onto Im_empty. Lower panel: same power spectra as in the upper panel, divided by the Im_empty line.