Local Toomre parameter for the relaxed disc at t = 0 for the gasLow and gasHigh simulations. The dashed line shows the mean Toomre parameter of the disc for the gasLow simulation 〈Q〉 = 3.29 > 1 and for the gasHigh simulation 〈Q〉 = 0.72 < 1. One therefore expects the gasHigh simulation to fragment independently of external pressure enhancement, whereas the gasLow simulations are not expected to fragment into many clumps. The fact that the pressur-enhanced simulations of the gasLow galaxies shows a significant increase in the number of clumps compared to no-pressure enhancement demonstrates that external pressure can stimulate the fragmentation of a disc even if it is Toomre-stable.