Top panels: optical image (left), total H I  map (middle), and H I  velocity field (right). The dashed ellipse corresponds to the disc model described in Sect. 5.1. The cross and dashed line illustrate the kinematical centre and major axis, respectively. In the bottom-left corner, we show the linear scale (optical image) and the H I  beam (total H I  map and velocity field) as given in Table 6. In the total H I  map, contours are at ~4.5, 9, 13.5, 18, and 22.5 M_⊙ pc^-2. Bottom panels: PV diagrams obtained from the observed cube (left), model cube (middle), and residual cube (right) along the major and minor axes. Solid contours range from 2σ to 8σ in steps of 1σ. Dashed contours range from −2σ to −4σ in steps of −1σ. The horizontal and vertical lines correspond to the systemic velocity and dynamical centre, respectively.