Spiral pattern speeds Ω_s,1(R), Ω_s,2(R) and Ω_s,3(R) of the multiple spiral modes moving at different pattern speeds of Model A in Spitoni et al. (2023) are indicated by the three coloured horizontal lines. Inner and outer spiral structures (moving with the above-mentioned pattern speeds) are also indicated by the thicker grey, blue and green light-blue, respectively. The disc angular velocity Ω_d(R) computed by Roca-Fàbrega et al. (2014) is indicated with the dotted line. The 2:1 and 4:1 outer and inner Lindblad resonances (OLR and ILR) occur along the solid and dashed black curves, respectively. Resonances have been computed as Ω_p2(R) = Ω_d(R) ± κ/2 and Ω_p4(R) = Ω_d(R) ± κ/4, respectively where κ is the local radial epicyclic frequency. The long vertical dashed lines show the positions of the co-rotation radii assuming the three different Ω_S values.