Ratio of mean pairwise velocities between fiducial hydrodynamic and gravity-only runs at z = 0. The gas and dark matter ratios are displayed in both panels in solid and dashed green lines, respectively. Upper panel: Ratio of mean pairwise velocities with dark matter velocity field sampled at gas positions (dashed-dotted lines) and gas velocity field sampled at dark matter positions (dotted lines). Lower panel: Predictions from linear theory assuming different boosts for velocity and density power spectra, as indicated by the legend. The details of the procedure are explained in the main text.