Colour coded images showing the ratio of mean (large-scale) to rms for the galaxies: from left to right models 75, 76 and 77 at approximate times 13.2 Gyr. The fields are averaged over 1 kpc. The continuous contours delineate the regions (“arms”) where field is injected; these rotate rigidly, with pattern speed such that the corotation radius is at fractional radius r ≈ 0.7.