Same as Fig. 8, but now showing the results for the idealized case of a high-velocity scatterer and a point source discussed in Appendix A.2. The polarized spectrum is identical to the flux spectrum except that it is redshifted. If we increase the velocity of the scatterer from 3000 (blue) to 9000 km s⁻¹ (red), F_Q remains the same except for the increased redshift. The similarity between the intrinsic and scattered spectra is easily seen in the middle panel. However, the polarization P (bottom panel) is much more complicated because of the velocity shifts. Line photons can be scattered into wavelengths where there is little flux, and hence produce a strong enhancement in the polarization, and even spikes in polarization, at those wavelengths. Retrieving information on the scatterer by analyzing P is more difficult than by inspecting F_Q.