Bottom panel: composite line profile of four SiII absorption lines observed in the COS spectrum of Mrk 1486 (Rivera-Thorsen et al. 2015): λ = 1190 Å, λ = 1193 Å, λ = 1260 Å, and λ = 1304 Å. These lines all arise from the same ground state. The composite spectrum is transformed here in velocity space using the observed wavelength of stellar lines. Only in this figure, outflows show negative and inflows positive velocities. Upper panel: for each velocity bin, we plot the residual over the standard deviation between the observed SiII line and our best fit. The blue dashed lines correspond to 1σ deviation.