Cornering the axion-like particle explanation of quasar polarisations

In a series of paper, it has been shown that the distribution of polarisation position angles for visible light from quasars is not random in extremely large regions of the sky. As explained in a recent article, the measurement of vanishing circular polarisation for such quasars is an important problem for a mechanism involving the mixing with axion-like particles in external magnetic fields. In this note, we stress that a recent report of similar coherent orientations of polarisation in radiowaves further disfavours the need for such particles, as an effect at these wavelengths would be extremely suppressed or would directly contradict data.Comment: 5 pages; no figures; accepted for publication as a Brief Report in Physical Review

Polarization alignments of radio quasars in JVAS/CLASS surveys

We test the hypothesis that the polarization vectors of flat-spectrum radio sources (FSRS) in the JVAS/CLASS 8.4-GHz surveys are randomly oriented on the sky. The sample with robust polarization measurements is made of $4155$ objects and redshift information is known for $1531$ of them. We performed two statistical analyses: one in two dimensions and the other in three dimensions when distance is available. We find significant large-scale alignments of polarization vectors for samples containing only quasars (QSO) among the varieties of FSRS's. While these correlations prove difficult to explain either by a physical effect or by biases in the dataset, the fact that the QSO's which have significantly aligned polarization vectors are found in regions of the sky where optical polarization alignments were previously found is striking.Comment: 13 pages, 9 figures, submitted to MNRA

Confirmation of the existence of coherent orientations of quasar polarization vectors on cosmological scales

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 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.Comment: Accepted for publication in Astronomy & Astrophysic

A changing-look AGN to be probed by X-ray polarimetry

Active galactic nuclei (AGN) produce the highest intrinsic luminosities in the Universe from within a compact region. The central engine is thought to be powered by accretion onto a supermassive black hole. A fraction of this huge release of energy influences the evolution of the host galaxy, and in particular, star formation. Thus, AGN are key astronomical sources not only because they play an important role in the evolution of the Universe, but also because they constitute a laboratory for extreme physics. However, these objects are under the resolution limit of current telescopes. Polarimetry is a unique technique capable of providing us with information on physical AGN structures. The incoming new era of X-ray polarimetry will give us the opportunity to explore the geometry and physical processes taking place in the innermost regions of the accretion disc. Here we exploit this future powerful tool in the particular case of changing-look AGN, which are key for understanding the complexity of AGN physics.Comment: 9 pages, 1 figures, published by Galaxies under the special issue "The Bright Future of Astronomical X-ray Polarimetry

Alignment of quasar polarizations with large-scale structures

We have measured the optical linear polarization of quasars belonging to Gpc-scale quasar groups at redshift z ~ 1.3. Out of 93 quasars observed, 19 are significantly polarized. We found that quasar polarization vectors are either parallel or perpendicular to the directions of the large-scale structures to which they belong. Statistical tests indicate that the probability that this effect can be attributed to randomly oriented polarization vectors is of the order of 1%. We also found that quasars with polarization perpendicular to the host structure preferentially have large emission line widths while objects with polarization parallel to the host structure preferentially have small emission line widths. Considering that quasar polarization is usually either parallel or perpendicular to the accretion disk axis depending on the inclination with respect to the line of sight, and that broader emission lines originate from quasars seen at higher inclinations, we conclude that quasar spin axes are likely parallel to their host large-scale structures.Comment: Accepted for publication in Astronomy and Astrophysic

New constraints on very light pseudoscalars

Nearly massless axion-like particles are of interest for astrophysical observations, and some constraints on their parameter space do exist in the literature. Here, we propose to put new constraints on these particles using polarisation and, in particular, the polarisation differences observed between different quasar classes.Comment: Contributed to the "7th Patras Workshop on Axions, WIMPs and WISPs", Mykonos June 26 - July 1 201

Optical linear polarization measurements of quasars obtained with the 3.6m telescope at the La Silla Observatory

We report 192 previously unpublished optical linear polarization measurements of quasars obtained in April 2003, April 2007, and October 2007 with the European Southern Observatory Faint Object Spectrograph and Camera (EFOSC2) instrument attached to the 3.6m telescope at the La Silla Observatory. Each quasar was observed once. Among the 192 quasars, 89 have a polarization degree $p \geq 0.6\%$, 18 have $p \geq 2\%$, and two have $p \geq 10\%$.Comment: Accepted for publication in A&

On the circular polarisation of light from axion-photon mixing

From the analysis of measurements of the linear polarisation of visible light coming from quasars, the existence of large-scale coherent orientations of quasar polarisation vectors in some regions of the sky has been reported. Here, we show that this can be explained by the mixing of the incoming photons with nearly massless pseudoscalar (axion-like) particles in extragalactic magnetic fields. We present a new treatment in terms of wave packets and discuss its implications for the circular polarisation.Comment: Contributed to "Invisible Universe International Conference", Paris, June 29 - July 3 2009. To be published in AIP proceeding

The different origins of high- and low-ionization broad emission lines revealed by gravitational microlensing in the Einstein cross

We investigate the kinematics and ionization structure of the broad emission line region of the gravitationally lensed quasar QSO2237+0305 (the Einstein cross) using differential microlensing in the high- and low-ionization broad emission lines. We combine visible and near-infrared spectra of the four images of the lensed quasar and detect a large-amplitude microlensing effect distorting the high-ionization CIV and low-ionization H$\alpha$ line profiles in image A. While microlensing only magnifies the red wing of the Balmer line, it symmetrically magnifies the wings of the CIV emission line. Given that the same microlensing pattern magnifies both the high- and low-ionization broad emission line regions, these dissimilar distortions of the line profiles suggest that the high- and low-ionization regions are governed by different kinematics. Since this quasar is likely viewed at intermediate inclination, we argue that the differential magnification of the blue and red wings of H$\alpha$ favors a flattened, virialized, low-ionization region whereas the symmetric microlensing effect measured in CIV can be reproduced by an emission line formed in a polar wind, without the need of fine-tuned caustic configurations.Comment: 11 pages, 4 figures, A&

Quasar Host Orientation and Polarization: Insights into the Type 1/Type 2 Dichotomy

We investigate correlations between the optical linear polarization position angle and the orientation of the host galaxy/extended emission of Type 1 and Type 2 Radio-Loud (RL) and Radio-Quiet (RQ) quasars. We have used high resolution Hubble Space Telescope (HST) data and deconvolution process to obtain a good determination of the host galaxy orientation. With these new measurements and a compilation of data from the literature, we find a significant correlation between the polarization position angle and the position angle of the major axis of the host galaxy/extended emission. The correlation appears different for Type 1 and Type 2 objects and depends on the redshift of the source. Interpretations in the framework of the unification model are discussed.Comment: 3 pages, 1 figure, to appear in "The Nuclear Region, Host Galaxy and Environment of Active Galaxies", eds. E. Benitez, I. Cruz-Gonzalez and Y. Krongold, RevMexAA (Serie de Conferencias