Color map of the surface density Σ(ρ, ϕ) corresponding to the potential V = V_d + V_b + V_sp (see text), as viewed in the bar’s rotating frame, at four different snapshots, namely t = 0 (top left), t = T/4 (top right), t = T/2 (bottom left), and t = 3T/4 (bottom right), where T = π/|Ω_sp − Ω_bar|. Since Ω_sp <  Ω_bar, the spirals have a relative clockwise angular displacement in time with respect to the bar. However, the morphological continuity between the bar and spirals is retained in all of these snapshots.