Top panel: Diskfit model, with perturbations from a bar at PA 0°, fit to the CO velocity field (left panel) and the resulting residual CO velocity field (observed − model) (right panel). Bottom panel: illustrative bar-perturbed velocity fields resulting from our linearized epicyclic perturbation models (see text) and using λ = 0.2 and Ω = 120km s⁻¹ kpc. The left (right) panel shows the results when setting the intrinsic rotation curve as that from C14 (our Bertola model fit to the stellar velocity field).