Top: relative strength of the first two Fourier modes in the gravitational potential (Q_{m = 1,2}) as a function of radius, compared to the total strength of the non-axisymmetric perturbation Q_T. Bottom: phases of the first two Fourier modes in the gravitational potential φ_{m = 1,2}, measured counter-clockwise from the major axis of the galaxy on the deprojected image (represented here in radians from −π to π).