Issue |
A&A
Volume 367, Number 2, February IV 2001
|
|
---|---|---|
Page(s) | 381 - 387 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361:20000443 | |
Published online | 15 February 2001 |
Confirmation of the existence of coherent orientations of quasar polarization vectors on cosmological scales*
1
European Southern Observatory, Casilla 19001, Santiago 19, Chile
2
Institut d'Astrophysique, Université de Liège, 5 Av. de Cointe, 4000 Liège, Belgium
Received:
4
September
2000
Accepted:
5
December
2000
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 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.
Key words: cosmology: large-scale structure of the Universe / quasars: general / polarization
© ESO, 2001
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