Azimuthal profile of the normalised fluctuations of the gas (top), stars (middle), and SFR (bottom) surface densities at t = 2500 Myr. These are compared with the normalised fluctuations of the contributions of the external non-axisymmetric components of the potential, with the bar (green) and the spirals (pink), associated with the right vertical axis of each panel, which is reversed so that lower values are on top. The data have been averaged over a radius range of 1 kpc, and the shaded area represents the radial variations.