Stellar (orange) and ionized gas (blue) rotation curves in UG101, derived from a slit oriented according to the stellar kinematic PA (see text and also Fig. 7). Points show the average velocities within each slit element, while solid curves correspond to a 1D LOESS local regression (Cappellari et al. 2013), with shaded areas indicating the 3σ uncertainty. The x-axis corresponds to the distance along the slit from the galaxy center, with positive values corresponding to the side facing the companion (indicated in the figure). The dashed vertical lines mark a distance of R_e, while the dotted line indicates a distance of 2 R_e. The bottom frame shows the difference between gas and stellar velocities.