Polarization of the C iv line. From top to bottom, total flux F(λ), (in arbitrary units), linear polarization degree p(λ), (in %), polarized flux F(λ)×p(λ), (in arbitrary units), and polarization position angle θ(λ) (in degree). The left panel refers to image A and the right panel to image D. The position of the broad emission line, the low-velocity BAL and the high-velocity BAL are indicated.