All Figures

$\begin{figure} \par {\includegraphics*[width=11cm,clip]{2163fig1.ps} }\end{figure}$ Figure 1: Top: the distribution of the polarization angles of stars from the Heiles catalogue (Heiles 2000). Only high latitude stars ( $\vert b_{\scriptscriptstyle \rm II}\vert \geq 30^{\circ }$ ) with polarization angles having uncertainties $\sigma _{\theta } \leq 14^{\circ }$ are considered. The NGP and SGP regions are illustrated separately. The darker histograms refer to stars at distances $\geq$ 200 pc. Bottom: the distribution of the polarization angles of field stars measured on QSO frames. Data from previous papers are included. Only those objects with uncertainties on polarization angles $\sigma _{\theta } \leq 14^{\circ }$ are illustrated.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{2163fi2a.ps}\par\vspace*{3mm} \includegraphics[width=7cm,clip]{2163fi2b.ps} \end{figure}$ Figure 2: The distribution of the debiased polarization degree of field stars in the NGP region ( top, from the 2002 data) and in the SGP region ( bottom, from the 2000 and 2003 data). The correction by the systematic $\overline {q}_{\star }$ and $\overline {u}_{\star }$ is done. Only measurements with an error on the polarization degree <0.3% are represented.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2163fig3.eps} \end{figure}$ Figure 3: The measured polarization angle $\theta$ (from Table 4) is reported against the published value $\theta _l$ (from Table 5). Due to its very low polarization level and highly uncertain $\theta$ in Table 4, 2MA J1714+2602 is not represented here.
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{2163fig4.ps} \end{figure}$ Figure 4: This figure compares, for the NGP region (2002 data), the QSO polarization angle $\theta _{0}$ , uncorrected for the systematic $\overline {q}_{\star }$ and $\overline {u}_{\star }$ , to the polarization angle $\theta '$ derived after a frame by frame subtraction of the Stokes parameters of field stars (when the latter measurements were possible). Only QSOs with either $p_0 \geq 0.6$ % or $p' \geq 0.6$ % are plotted. For most objects, $\vert\theta ' - \theta _0 \vert$ is within 5 $^{\circ }$ . As a reference, the dashed line represents simulated data obtained by subtracting a systematic polarization of 0.2% oriented at 70 $^{\circ }$ (cf. Fig. 1) from a polarization of 0.6% randomly oriented. Together with the distributions of $\theta _{0}$ and $\theta '$ , the histograms illustrate the distribution of polarization angle $\theta$ reported in Table 4 and corrected for the systematic $\overline {q}_{\star }$ and $\overline {u}_{\star }$ (QSOs with $p \geq 0.6$ % only).
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{2163fig5.ps} \end{figure}$ Figure 5: Same as Fig. 4, but for QSOs from the SGP region (2000 and 2003 data). For most objects, $\vert\theta ' - \theta _0 \vert$ is also within 5 $^{\circ }$ . The dashed line represents simulated data obtained by subtracting a systematic polarization of 0.2% oriented at 135 $^{\circ }$ (cf. Fig. 1) from a polarization of 0.6% randomly oriented.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{2163fi2a.ps}\par\vspace*{3mm} \includegraphics[width=7cm,clip]{2163fi2b.ps} \end{figure}$	Figure 2: The distribution of the debiased polarization degree of field stars in the NGP region ( top, from the 2002 data) and in the SGP region ( bottom, from the 2000 and 2003 data). The correction by the systematic $\overline {q}_{\star }$ and $\overline {u}_{\star }$ is done. Only measurements with an error on the polarization degree <0.3% are represented.
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2163fig3.eps} \end{figure}$	Figure 3: The measured polarization angle $\theta$ (from Table 4) is reported against the published value $\theta _l$ (from Table 5). Due to its very low polarization level and highly uncertain $\theta$ in Table 4, 2MA J1714+2602 is not represented here.
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$\begin{figure} \par\includegraphics[width=15cm,clip]{2163fig5.ps} \end{figure}$	Figure 5: Same as Fig. 4, but for QSOs from the SGP region (2000 and 2003 data). For most objects, $\vert\theta ' - \theta _0 \vert$ is also within 5 $^{\circ }$ . The dashed line represents simulated data obtained by subtracting a systematic polarization of 0.2% oriented at 135 $^{\circ }$ (cf. Fig. 1) from a polarization of 0.6% randomly oriented.
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