2 New observations and compilation of data

In Paper I, we identified a region in the sky (region A1) where nearly all quasar polarization position angles lie in the range 146 $\hbox{$^\circ$ }$-46 $\hbox{$^\circ$ }$. This region is delimited in right ascension by $11^{\rm h}$ $15^{\rm m} \leq \alpha \leq 14^{\rm h}$ $29^{\rm m}$ and in redshift by $1.0 \leq z \leq 2.3$. A new sample of quasars located in this region was therefore selected, mainly from the quasar catalogues of Véron-Cetty & Véron (1998) and Hewitt & Burbidge (1993). This sample was observed during two runs at ESO La Silla in 1998 and 1999, using the ESO 3.6 m telescope equipped with EFOSC2 in its polarimetric mode. In order to minimize the contamination by interstellar polarization in our Galaxy, only objects at high galactic latitudes $\vert b_{\scriptscriptstyle \rm II}\vert \geq 35\hbox{$^\circ$ }$ were considered. The selection of the targets at the telescope was not random: the brightest objects were given higher priority as well as objects at the center of the alignment region where the orientation effect is suspected to be stronger. Also, radio-loud and broad absorption line (BAL) quasars were preferred since these objects are more likely to be significantly polarized (Impey & Tapia 1990; Hutsemékers et al. 1998; Schmidt & Hines 1999). In this view, 3 BAL quasars recently discovered by Brotherthon et al. (1998) were added to the sample. At the end, polarimetric data were secured for 28 quasars belonging to region A1, with a typical uncertainty of 0.2% on the polarization degree. About half of them appear significantly polarized. These data are presented in Lamy & Hutsemékers (2000) with full account of the observation and reduction details.

   

Table 1: The additional sample of polarized quasars

Object	$b_{\scriptscriptstyle \rm II}$	z	p	$\sigma_{\rm p}$	$\theta$	$\sigma_{\theta}$	Ref
(B1950)	( $\hbox{$^\circ$ }$)		(%)	(%)	( $\hbox{$^\circ$ }$)	( $\hbox{$^\circ$ }$)
B0004+017	-59	1.711	1.29	0.28	122	6	8
B0010-002	-61	2.145	1.70	0.77	116	13	8
B0025-018	-64	2.076	1.16	0.52	109	13	8
B0046-315	-86	2.721	13.30	2.00	159	4	7
B0109-014	-64	1.758	1.77	0.35	76	6	8
B0117-180	-79	1.790	1.40	0.46	13	10	8
B0226-104	-62	2.256	2.51	0.25	165	3	8
B0422-380	-45	0.782	6.20	3.00	173	14	7
B0448-392	-40	1.288	2.90	1.00	49	10	7
B0759+651	+32	0.148	1.45	0.14	119	3	8
B0846+156	+33	2.910	0.80	0.21	151	8	9
B0856+172	+36	2.320	0.70	0.24	0	10	9
B0932+501	+47	1.914	1.39	0.16	166	3	8
B1009+023	+44	1.350	0.77	0.19	137	7	9
B1051-007	+50	1.550	1.90	0.19	90	3	9
B1157-239	+37	2.100	1.33	0.17	95	4	9
B1157+014	+61	1.990	0.76	0.18	39	7	9
B1203+155	+74	1.630	1.54	0.20	30	4	9
B1205+146	+74	1.640	0.83	0.18	161	6	9
B1215+127	+73	2.080	0.62	0.24	17	12	9
B1216-010	+61	0.415	6.90	0.80	8	3	7
B1219+127	+74	1.310	0.68	0.20	151	9	9
B1222-016	+60	2.040	0.80	0.22	119	8	9
B1235-182	+44	2.190	1.02	0.18	171	5	9
B1239+099	+72	2.010	0.82	0.18	161	6	9
B1256-220	+41	1.306	5.20	0.80	160	4	7
B1256-175	+45	2.060	0.91	0.19	71	6	9
B1302-102	+52	0.286	1.00	0.40	70	11	7
B1305+001	+62	2.110	0.70	0.22	151	9	9
B1333+286	+80	1.910	5.88	0.20	161	1	9
B1402+436	+68	0.324	7.55	0.22	33	1	8
B1443+016	+52	2.450	1.33	0.23	159	5	9
B1452-217	+33	0.773	12.40	1.50	60	3	7
B1500+084	+54	3.940	1.15	0.33	100	9	9
B1524+517	+52	2.873	2.71	0.34	94	4	8
B1556+335	+50	1.650	1.31	0.47	70	10	8
B2115-305	-44	0.980	3.40	0.40	67	3	7
B2118-430	-45	2.200	0.66	0.20	133	9	9
B2128-123	-41	0.501	1.90	0.40	64	6	7
B2135-147	-43	0.200	1.10	0.40	100	10	7
B2201-185	-51	1.814	1.43	0.51	7	10	8
B2341-235	-74	2.820	0.64	0.20	122	9	9
B2358+022	-58	1.872	2.12	0.51	45	7	8
B0019+011	-61	2.124	0.76	0.19	26	7	8
B0059-275	-88	1.590	1.45	0.23	171	5	9
B0146+017	-58	2.909	1.23	0.21	141	5	8
B0946+301	+50	1.216	0.85	0.14	116	5	8
B1011+091	+49	2.266	1.54	0.23	136	4	8
B1151+117	+69	0.180	0.72	0.18	100	7	9
B1246-057	+57	2.236	1.96	0.18	149	3	8
B1413+117	+65	2.551	2.53	0.29	53	3	8
B2240-370	-61	1.830	2.10	0.19	28	3	9

References: (7) Visvanathan & Wills 1998, (8) Schmidt & Hines 1999, (9) Lamy & Hutsemékers 2000.

In the meantime, two major quasar polarimetric surveys -obviously not restricted to region A1- have been published by Visvanathan & Wills (1998) and by Schmidt & Hines (1999). Several of their targets are located in region A1, but most of them are unfortunately redundant with ours and generally measured with less accuracy. All these new data have been compiled, also including a few additional measurements we did ourselves in the framework of a polarimetric study of radio-loud BAL quasars (Hutsemékers & Lamy 2000). The new polarimetric data are summarized in Table 1. They refer to quasars distributed all over the sky, which complement the sample of 170 polarized quasars studied in Paper I. The 43 objects reported in the first part of Table 1 are significantly polarized and fulfil the criteria defined in Paper I: $p \geq 0.6 \%$, $\sigma _{\theta } \leq 14\hbox {$^\circ $ }$, and $\vert b_{\scriptscriptstyle \rm II}\vert \geq 30\hbox{$^\circ$ }$, where p is the polarization degree and $\sigma_{\theta}$ the uncertainty of the polarization position angle $\theta$. These constraints ensure that most objects are significantly and intrinsically polarized with little contamination by the Galaxy, and that the polarization position angles are measured with a reasonable accuracy (Paper I). If an object has been observed more than once, only the best value is kept i.e. the measurement with the smallest uncertainty $\sigma_{\rm p}$ on the polarization degree. Let us recall that our previous sample of 170 objects was similarly selected from 525 measurements compiled from the literature. The second part of Table 1 lists quasars already studied in Paper I, and for which better data (i.e. with a smaller $\sigma_{\rm p}$) have been obtained in the recent surveys. Note that these new measurements are in good agreement with the older ones, as well as measurements obtained by different authors, providing confidence in the quality of the data. Together with the data from Paper I, the total sample of polarized quasars then amounts to 213 objects distributed all over the sky.