Velocity projection of ξ(Δr_⊥, Δv). Blue squares represent the arc data. The 1σ errors (in pink) include both the bootstrapping analysis and the Poisson statistics described in Sect. 6.3 but are dominated by the latter. Dashed curves indicate the signal produced by a velocity field distributed as $\mathcal{N}(0,{\delta }_v^2)$, where δ_v are the individual measurement errors. Green curves show the model prediction (Sect. 7.2.4).