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See detailLarge Scale Correlations of Quasar Polarization Vectors: Hints of Extreme Scale Structures?
Cabanac, R. A.; Hutsemekers, Damien ULg; Sluse, D. et al

in Astronomical Polarimetry: Current Status and Future Directions. ASPC 343 (2005, December 01)

A survey measuring quasar polarization vectors has been started in two regions towards the North and South Galactic Poles. Here, we review the discovery of significant correlations of orientations of ... [more ▼]

A survey measuring quasar polarization vectors has been started in two regions towards the North and South Galactic Poles. Here, we review the discovery of significant correlations of orientations of polarization vectors over huge angular distances. We report new results including a larger sample of the quasars confirming the existence of coherent orientations at redshifts z>1. [less ▲]

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See detailMapping extreme-scale alignments of quasar polarization vectors
Hutsemekers, Damien ULg; Cabanac, R.; Lamy, H. et al

in Astronomy and Astrophysics (2005), 441

Based on a new sample of 355 quasars with significant optical polarization and using complementary statistical methods, we confirm that quasar polarization vectors are not randomly oriented over the sky ... [more ▼]

Based on a new sample of 355 quasars with significant optical polarization and using complementary statistical methods, we confirm that quasar polarization vectors are not randomly oriented over the sky with a probability often in excess of 99.9%. The polarization vectors appear coherently oriented or aligned over huge ( 1 Gpc) regions of the sky located at both low (z Ë 0.5) and high (z Ë 1.5) redshifts and characterized by different preferred directions of the quasar polarization. In fact, there seems to exist a regular alternance along the line of sight of regions of randomly and aligned polarization vectors with a typical comoving length scale of 1.5 Gpc. Furthermore, the mean polarization angle bartheta appears to rotate with redshift at the rate of 30° per Gpc. The symmetry of the the bartheta -z relation is mirror-like, the mean polarization angle rotating clockwise with increasing redshift in North Galactic hemisphere and counter-clockwise in the South Galactic one. These characteristics make the alignment effect difficult to explain in terms of local mechanisms, namely a contamination by interstellar polarization in our Galaxy. While interpretations like a global rotation of the Universe can potentially explain the effect, the properties we observe qualitatively correspond to the dichroism and birefringence predicted by photon-pseudoscalar oscillation within a magnetic field. Interestingly, the alignment effect seems to be prominent along an axis not far from preferred directions tentatively identified in the Cosmic Microwave Background maps. Although many questions and more particularly the interpretation of the effect remain open, alignments of quasar polarization vectors appear as a promising new way to probe the Universe and its dark components at extremely large scales. [less ▲]

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See detailAlignments of quasar polarization vectors (Hutsemekers+, 2005)
Hutsemekers, Damien ULg; Cabanac, R.; Lamy, H. et al

Textual, factual or bibliographical database (2005)

The table contains linear polarization measurements for 355 QSOs. (3 data files).

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See detailNew optical polarization measurements of quasi-stellar objects. The data
Sluse, D.; Hutsemekers, Damien ULg; Lamy, H. et al

in Astronomy and Astrophysics (2005), 433

New linear polarization measurements (mainly in the V band) are presented for 203 quasi-stellar objects (QSOs). The sample is made up of 94 QSOs located in the North Galactic Pole (NGP) region and of 109 ... [more ▼]

New linear polarization measurements (mainly in the V band) are presented for 203 quasi-stellar objects (QSOs). The sample is made up of 94 QSOs located in the North Galactic Pole (NGP) region and of 109 QSOs in the South Galactic Pole (SGP) region. First time measurements have been obtained for 184 QSOs. Among them, 109 known radio-emitters, 42 known Broad Absorption Line (BAL) QSOs, and 1 gravitationally lensed quasi-stellar object. We found high polarization levels (p > 3%) for 12 QSOs, including the BAL QSO <ASTROBJ>SDSS J1409+0048</ASTROBJ>. For 10 objects, measurements obtained at different epochs do exist. Two of them show evidence for variability: the highly polarized BL Lac candidate <ASTROBJ>PKS 1216-010</ASTROBJ> and the radio source <ASTROBJ>PKS 1222+037</ASTROBJ>. Based on observations collected at the European Southern Observatory (ESO, La Silla and Paranal). Table 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/757 [less ▲]

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See detailOptical polarization of 203 QSOs (Sluse+, 2005)
Sluse, D.; Hutsemekers, Damien ULg; Lamy, H. et al

Textual, factual or bibliographical database (2004)

This Table contains linear polarization measurements (mainly in the V band) of 203 QSOs. First time measurements have been obtained for 184 objects. Among them 109 known radio emitters, 42 BAL and 1 ... [more ▼]

This Table contains linear polarization measurements (mainly in the V band) of 203 QSOs. First time measurements have been obtained for 184 objects. Among them 109 known radio emitters, 42 BAL and 1 gravitationally lensed QSO. (1 data file). [less ▲]

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See detailPolarization properties of broad absorption line QSOs: New statistical clues
Lamy, H.; Hutsemekers, Damien ULg

in Astronomy and Astrophysics (2004), 427

We report the results of several statistical tests performed on a large sample of 139 broad absorption line (BAL) QSOs with good quality optical spectra and/or optical polarization data. Correlations ... [more ▼]

We report the results of several statistical tests performed on a large sample of 139 broad absorption line (BAL) QSOs with good quality optical spectra and/or optical polarization data. Correlations between ten optical indices and the polarization degree p[SUB]0[/SUB] are systematically searched for. We find six significant non-trivial correlations. In order to identify the most important correlations, we perform a principal component analysis with a sample of 30 BAL QSOs and eight quantities (including p[SUB]0[/SUB]). Most of the variance (Ë 57%) in the data is contained in two principal components called PC1 and PC2. PC1 is mainly dominated by the correlation between the balnicity index BI and the strength of the Fe II emission; it may be driven by the accretion rate of matter onto the central compact object. The variance in PC2 is essentially due to the anti-correlation between p[SUB]0[/SUB] and the detachment index DI, indicating that BAL QSOs with P Cygni profiles (DIâ ª) are usually more polarized than those objects with C IV absorption troughs well detached from the corresponding emission lines (DIâ «). We show that PC2 may be related to the orientation of the BAL QSOs with respect to the line of sight. We also present new spectropolarimetric observations of six BAL QSOs. By adding spectropolarimetric data from the literature, we build a sample of 21 BAL QSOs for which we define four spectropolarimetric indices describing the polarization properties of the absorption and emission lines. We find that the polarization of the C III]] emission line is systematically higher than the polarization of the C IV emission line, and that the highest polarization in the troughs is correlated to the balnicity index. Another important result emerging from the statistical tests performed on this spectropolarimetric sample is a possible anti-correlation between the detachment index and a quantity SI which measures the ratio of the depths of the C IV absorption in the polarized flux and in the total flux. This correlation indicates that in BAL QSOs with P cygni profiles, the BAL troughs in the polarized flux are nearly as deep as in the total flux while, in BAL QSOs with detached absorptions, the BAL troughs in the polarized flux are much weaker than in the total flux. We show that our main results may be explained in the framework of a ``two-component'' wind model which is a natural extension of the classical wind-from-disk models. In this model, the broad absorption occurs in a dense equatorial wind emerging from the accretion disk, while scattering and polarization mainly take place in a polar region. The orientation relative to the observer drives the correlations p[SUB]0[/SUB] - DI and DI - SI. While most of our observations can be explained within this framework, there are also several indications that other polarization mechanisms, and more particularly resonance scattering, may also be at work. Based on observations collected at the European Southern Observatory (ESO, La Silla). Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: / / cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/427/107 [less ▲]

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See detailPolarization in BAL QSOs (Lamy+, 2004)
Lamy, H.; Hutsemekers, Damien ULg

Textual, factual or bibliographical database (2004)

Table 1 contains optical properties of 139 BAL QSOs. It is essentially a compilation of 93 BAL QSOs coming from large polarization surveys. In addition, we also consider 46 BAL QSOs with good quality ... [more ▼]

Table 1 contains optical properties of 139 BAL QSOs. It is essentially a compilation of 93 BAL QSOs coming from large polarization surveys. In addition, we also consider 46 BAL QSOs with good quality optical (UV rest-frame) spectra but no polarization data. (1 data file). [less ▲]

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See detailQ0059-2735: A Hybrid Starburst/Broad Absorption Line QSO ? Clues from Spectropolarimetry
Hutsemekers, Damien ULg; Lamy, H.

in Mass Outflow in Active Galactic Nuclei: New Perspectives. ASPC 255 (2002)

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See detailThe Polarization Properties of Broad Absorption Line QSOs: Observational Results
Hutsemekers, Damien ULg; Lamy, H.

in Mass Outflow in Active Galactic Nuclei: New Perspectives. ASPC 255 (2002)

Correlations between BAL QSO intrinsic properties and polarization have been searched for. Some results are summarized here, providing possible constraints on BAL outflow models.

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See detailConfirmation of the existence of coherent orientations of quasar polarization vectors on cosmological scales
Hutsemekers, Damien ULg; Lamy, H.

in Astronomy and Astrophysics (2001), 367

In order to verify the existence of coherent orientations of quasars polarization vectors on very large scales, we have obtained new polarization measurements for a sample of quasars located in a given ... [more ▼]

In order to verify the existence of coherent orientations of quasars polarization vectors on very large scales, we have obtained new polarization measurements for a sample of quasars located in a given region of the three-dimensional Universe where the range of polarization position angles was predicted in advance. For this new sample, the hypothesis of uniform distribution of polarization position angles may be rejected at the 1.8% significance level on the basis of a simple binomial test. This result provides an independent confirmation of the existence of alignments of quasar polarization vectors on very large scales. In total, out of 29 polarized quasars located in this region of the sky, 25 have their polarization vectors coherently oriented. This alignment occurs at redshifts z =~ 1-2 suggesting the presence of correlations in objects or fields on Gpc scales. More global statistical tests applied to the whole sample of polarized quasars distributed all over the sky confirm that polarization vectors are coherently oriented in a few groups of 20-30 quasars. Some constraints on the phenomenon are also derived. Considering more particularly the quasars in the selected region of the sky, we found that their polarization vectors are roughly parallel to the plane of the Local Supercluster. But the polarization vectors of objects along the same line of sight at lower redshifts are not accordingly aligned. We also found that the known correlations between quasar intrinsic properties and polarization are not destroyed by the alignment effect. Several possible mechanisms are discussed, but the interpretation of this orientation effect remains puzzling. Based in part on observations collected at the European Southern Observatory (ESO, La Silla). [less ▲]

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See detailThe optical polarization of radio-loud and radio-intermediate broad absorption line quasi-stellar objects
Hutsemekers, Damien ULg; Lamy, H.

in Astronomy and Astrophysics (2000), 358

On the basis of a sample of approximately 50 broad absorption line quasi-stellar objects (BAL QSOs), we investigate possible correlations between BAL QSO radio properties and other spectral ... [more ▼]

On the basis of a sample of approximately 50 broad absorption line quasi-stellar objects (BAL QSOs), we investigate possible correlations between BAL QSO radio properties and other spectral characteristics, including polarization. For this purpose new polarization data have been obtained. The main result of our statistical study is the absence of significant correlations between the radio-to-optical flux ratio R[SUP]star [/SUP] and all other quantities: the polarization p_0 of the continuum, the slope of the continuum, the balnicity and detachment indices which characterize the BAL profiles, and the terminal velocity of the flow v_max. The claimed anticorrelation between R[SUP]star [/SUP] and v_max is therefore not confirmed, as well as the correlation between R[SUP]star [/SUP] and p_0 predicted by some models. Although marginally significant, the only possible correlations occur for the BAL QSOs with low-ionization troughs. Based on observations collected at the European Southern Observatory (ESO, La Silla) [less ▲]

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See detailSpectropolarimetry of the iron low ionization broad absorption line quasar Q 0059-2735
Lamy, H.; Hutsemekers, Damien ULg

in Astronomy and Astrophysics (2000), 356(Letters), 9-12

We present optical (ultraviolet rest-frame) spectropolarimetric observations of the rare iron low ionization broad absorption line (BAL) QSO Q 0059-2735. The continuum polarization increases to the blue ... [more ▼]

We present optical (ultraviolet rest-frame) spectropolarimetric observations of the rare iron low ionization broad absorption line (BAL) QSO Q 0059-2735. The continuum polarization increases to the blue with a regular rotation of the polarization position angle, suggesting that at least two mechanisms are at the origin of the polarization. There is also some evidence for dilution by a ion {Fe}{ii} pseudo-continuum in emission. In the broad absorption lines, the polarization strongly rises, with the largest values ever reported. On the contrary, the ion {Fe}{ii} blends in absorption are not more polarized than the continuum, while they are clearly visible in the polarized flux. These different polarization properties of ion {Fe}{ii} absorption lines suggest a different origin and/or geometry. The observed properties of Q 0059-2735 are consistent with a hybrid QSO / starburst model. Based on observations collected at the European Southern Observatory, La Silla, Chile [less ▲]

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See detailOptical polarization of 47 quasi-stellar objects: The data
Lamy, H.; Hutsemekers, Damien ULg

in Astronomy and Astrophysics. Supplement Series (2000), 142

New broad-band linear polarization measurements are presented for a sample of 47 QSOs which includes 27 broad absorption line QSOs and 2 gravitational lens candidates. Tables 3 and 4 are also available in ... [more ▼]

New broad-band linear polarization measurements are presented for a sample of 47 QSOs which includes 27 broad absorption line QSOs and 2 gravitational lens candidates. Tables 3 and 4 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html Based on observations collected at the European Southern Observatory (ESO, La Silla). [less ▲]

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See detailOptical Polarization of 47 QSOs (Lamy+, 2000)
Lamy, H.; Hutsemekers, Damien ULg

Textual, factual or bibliographical database (2000)

New broad-band linear polarization measurements are presented for a sample of 47 QSOs which includes 27 broad absorption line QSOs and 2 gravitational lens candidates. (2 data files).

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See detailErratum : A procedure for deriving accurate linear polarimetric measurements
Lamy, H.; Hutsemekers, Damien ULg

in The Messenger (1999), 97

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See detailPolarimetry and Spectropolarimetry of a Sample of Broad Absorption Line Quasars
Lamy, H.; Hutsemekers, Damien ULg

in Structure and Kinematics of Quasar Broad Line Regions. ASPC 175 (1999)

Optical polarimetric and spectropolarimetric observations of a sample of broad absorption line QSOs were recently carried out with the 3.6m telescope and EFOSC1 in La Silla, Chile. Some preliminary ... [more ▼]

Optical polarimetric and spectropolarimetric observations of a sample of broad absorption line QSOs were recently carried out with the 3.6m telescope and EFOSC1 in La Silla, Chile. Some preliminary results are presented here with emphasis on interesting correlations between polarization and other quantities characterizing the optical spectra of the objects. [less ▲]

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See detailA procedure for deriving accurate linear polarimetric measurements.
Lamy, H.; Hutsemekers, Damien ULg

in The Messenger (1999), 96

The authors present here a procedure written within the ESO MIDAS reduction package with the aim of deriving semi-automatically linear polarisation data from CCD images obtained with beam-splitters such ... [more ▼]

The authors present here a procedure written within the ESO MIDAS reduction package with the aim of deriving semi-automatically linear polarisation data from CCD images obtained with beam-splitters such as those available at the ESO 3.6-m telescope equipped with EFOSC2 or at the VLT equipped with FORS1. The method is adequate for point-like objects and was used for measuring quasar polarisation. [less ▲]

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See detailPolarization properties of a sample of broad absorption line and gravitationally lensed quasars
Hutsemekers, Damien ULg; Lamy, H.; Remy, M.

in Astronomy and Astrophysics (1998), 340

New broad-band linear polarization measurements have been obtained for a sample of 42 optically selected QSOs including 29 broad absorption line (BAL) QSOs. The polarization properties of different sub ... [more ▼]

New broad-band linear polarization measurements have been obtained for a sample of 42 optically selected QSOs including 29 broad absorption line (BAL) QSOs. The polarization properties of different sub-classes have been compared, and possible correlations with various spectral indices searched for. The main results of our study are: (1) Nearly all highly polarized QSOs of our sample belong to the sub-class of BAL QSOs with low-ionization absorption features (LIBAL QSOs). (2) The range of polarization is significantly larger for LIBAL QSOs than for high-ionization (HI) BAL QSOs and non-BAL QSOs. (3) There is some indication that HIBAL QSOs as a class may be more polarized than non-BAL QSOs and therefore intermediate between LIBAL and non-BAL QSOs, but the statistics are not compelling from the sample surveyed thus far. (4) For LIBAL QSOs, the continuum polarization appears significantly correlated with the line profile detachment index, in the sense that LIBAL QSOs with P Cygni-type profiles are more polarized. No correlation was found with the strength of the low- or the high-ionization absorption features, nor with the strength or the width of the emission lines. These results are consistent with a scenario in which LIBAL QSOs constitute a different class of radio-quiet QSOs with more absorbing material and more dust. Higher maximum polarization can therefore be reached, while the actually measured polarization depends on the geometry and orientation of the system as do the line profiles. The observed correlation is interpreted within the framework of recent ``wind-from-disk'' models. Tables~2 and 3 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html}\fnmsep\thanks{Based on observations collected at the European Southern Observatory (ESO, La Silla) [less ▲]

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See detailQuasar polarization (Hutsemekers+ 1998)
Hutsemekers, Damien ULg; Lamy, H.; Remy, Marc

Textual, factual or bibliographical database (1998)

Table 2 contains optical (V) polarimetric measurements for 42 optically selected QSOs including 29 broad absorption line QSOs. Table 3 contains a series of spectral indices characterizing the broad ... [more ▼]

Table 2 contains optical (V) polarimetric measurements for 42 optically selected QSOs including 29 broad absorption line QSOs. Table 3 contains a series of spectral indices characterizing the broad absorption line QSOs. (2 data files). [less ▲]

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