Comparison of the SDSS image of the galaxies with the result of the simulation. Top panel a: model obtained using our N-body simulation with the general region of nucleus A (blue) and B (blue) highlighted. Middle panel b: optical SDSS image of galaxies SDSS J134420.86+663717.8, superimposed with contours starting at 10% in steps of 10%. Comparison of the two figures shows striking similarities in their morphology, especially in the shapes of the two tidal arms. Bottom panel c: at an angular resolution of about 1 arcsec, we show a smoothed velocity map obtained from the simulated data cubes. Contour levels are −200, −100, −20, 20, 100, 200 km s⁻¹. The dashed rectangular box shows the aperture along which the velocities used to plot the dashed green lines in the rotation curve in Fig. 8 were extracted.