Scenario I: Snapshot of the model M5 (S4M9) surface mass (left) and LOS velocity (right) projected with θ_sky = 18° corresponding to the BA–FI+P orbital solution with a final tangential velocity of $u_{\mathrm{t}}=100\mathrm{km}{\mathrm{s}}^{-1}$ (top rows). This model uses the low-mass dwarf model D1. The combined centre of mass for the stellar and dark matter distributions is marked with the white star, and the gas peak is marked with the white cross. Here the satellite is found passing over the perturbation added to the IGM with $\delta {\rho }_{\max }=100\times {\rho }_{\mathrm{IGM}}^{\mathrm{MW}}$. We also project the model with 0° (bottom row) to better reveal the transient offset between the gas and stars; however, this causes the transient LOS velocity gradient to vanish due the projection. The v_los maps are in the rest frame of the dwarf’s dark matter centre of mass. The contours on the leading side may cover the velocity map due to the strong compression, which can be avoided by zooming in the pdf version. We note that ${\mathrm{\Sigma }}_{\mathrm{gas}}=1{\mathrm{M}}_{\odot }{\mathrm{pc}}^{-2}$ corresponds here to N_HI = 1.2 × 10²⁰ cm⁻².