Outflow velocity as a function of the radial distance from the quasar position. Both R and v are projected quantities. To produce this plot, the outflowing clumps have been divided into bins of radial distance from the quasar (ΔR = 0.6 arcsec, i.e. ≃3 kpc). The plot shows the average velocity of the clumps within each bin (, where N is the number of clumps in each bin). The error bars in the x direction indicate the bin size. The error on ⟨ v ⟩ is given by , where σ_vi is the uncertainty on the average velocity v_i of a clump in outflow, estimated as explained in Appendix C.