In the combined ram pressure and tidal interaction simulation (RP-fid + TI-fid), the tidal interaction generates an S-shaped structure in the disk, and the ram pressure then peels back the gas from the extended spiral arms. The model is shown at time=611 Myr. For comparison the equivalent plots for the individual mechanisms can be seen at a similar simulation time in row 5 (left: TI-fid, RP-fid: right) of Fig. C.1. As a result, the young stars form outside the extended arms of the intermediate-age stars, and the SSD is driven to even higher values than is seen in the separate RP-fid or TI-fid model (see SSD evolution in Fig. 5; purple line of the left panel for the model shown here.)