A new test of uniformity for object orientations in astronomy

We briefly present a new coordinate-invariant statistical test dedicated to the study of the orientations of transverse quantities of non-uniformly distributed sources on the celestial sphere. These quantities can be projected spin-axes or polarization vectors of astronomical sources.Comment: Proceedings IAU Symposium No. 306, 201

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

A new analysis of quasar polarisation alignments

We propose a new method to analyse the alignment of optical polarisation vectors from quasars. This method leads to a definition of intrinsic preferred axes and to a determination of the probability $p^{\sigma}$ that the distribution of polarisation directions is random. This probability is found to be as low as 0.003% for one of the regions of redshift.Comment: 20 pages, 9 figure

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

Polarization power spectra and dust cloud morphology

In the framework of studies of the CMB polarization and its Galactic foregrounds, the angular power spectra of thermal dust polarization maps have revealed an intriguing E/B asymmetry and a positive TE correlation. In interpretation studies of these observations, magnetized ISM dust clouds have been treated as filamentary structures only; however, sheet-like shapes are also supported by observational and theoretical evidence. In this work, we study the influence of cloud shape and its connection to the local magnetic field on angular power spectra of thermal dust polarization maps. We simulate realistic filament-like and sheet-like interstellar clouds, and generate synthetic maps of their thermal dust polarized emission using the software $Asterion$. We compute their polarization power spectra in multipole range $\ell \in [100,500]$ and quantify the E/B power asymmetry through the $R_{EB}$ ratio, and the correlation coefficient $r^{TE}$ between T and E modes. We quantify the dependence of $R_{EB}$ and $r^{TE}$ values on the offset angle (between longest cloud axis and magnetic field) and inclination angle (between line-of-sight and magnetic field) for both cloud shapes embedded either in a regular or a turbulent magnetic field. We find that both cloud shapes cover the same regions of the ($R_{EB}$, $r^{TE}$) parameter space. The dependence on inclination and offset angles are similar for both shapes although sheet-like structures generally show larger scatter. In addition to the known dependence on the offset angle, we find a strong dependence of $R_{EB}$ and $r^{TE}$ on the inclination angle. The fact that filament-like and sheet-like structures may lead to polarization power spectra with similar ($R_{EB}$, $r^{TE}$) values complicates their interpretation. In future analyses, this degeneracy should be accounted for as well as the connection to the magnetic field geometry.Comment: 16 pages, 24 figures. Accepted for publication by A&

Anisotropic Orientations of Polarisations from quasar light

Presentation of the foundations of a new statistical test dedicated to the polarisation orientations analysis

Local alignments of parsec-scale AGN radiojets

Context.Coherence in the characteristics of neighboring sources in 2D and 3D space may suggest the existence of large-scale cosmic structures, which are useful for cosmological studies. Numerous works have been conducted to detect such features in global scalesas well as in confined areas of the sky. However, results are often contradictory and their interpretation remains controversial. Aims.We investigate the potential alignment of parsec-scale radio jets in localized regions of the coordinates-redshift space. Methods.We use data from the Astrogeo VLBI FITS image database to deduce jet directions of radio sources. We perform the search for statistical alignments between nearby sources and explore the impact of instrumental biases. Results.We unveil four regions for which the alignment between jet directions deviates from randomness at a significance level of more than 5 sigma and is unlikely due to instrumental systematics. Intriguingly, their locations coincide with other known large-scale cosmic structures and/or regions of alignments. Conclusions.If the alignments found are the result of physical processes, the discovered regions may designate some of the largest structures known to date.Comment: 11 pages, 9 figure

OC-0420: Improving quality of care in rectal cancer:the role of a central review platform in CTV delineation

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Between liveability and accessibility in the Bois de la Cambre

Il s’agit d’étudier les tensions qui existent entre accessibilité géographique et habitabilité urbaine à Bruxelles, en examinant le cas du Bois de la Cambre en tant que lieu de loisir et de passage. Nous nous intéressons d’abord aux 150 ans d’histoire de ce parc, avant de présenter une enquête exploratoire sur les préférences de la population en ce qui concerne l’aménagement du parc eu égard à la circulation automobile. L’étude fait apparaître une étroite corrélation entre cet aménagement et le mode de vie de chacun. Au fil de son histoire, l’aménagement du parc s’est fait surtout en réponse à des changements sociétaux d’ordre général au niveau des modes d’organisation de la vie des populations, plutôt qu’à un projet urbain explicite. De nos jours, les priorités exprimées par différents groupes de population pour l’aménagement du parc sont fonction de leur lieu de résidence, de leur mode de déplacement, de leur utilisation des espaces verts et de leur accès à ces derniers. Dans ce contexte, l’étude met en évidence la nécessité d’œuvrer autant à la mise en place d’autres solutions de mobilité concrètes qu’à l’élaboration de nouveaux imaginaires pour la ville et la mobilité.Aan de hand van het geval van het Ter Kamerenbos, dat zowel als doorgangsruimte als voor vrijetijdsdoeleinden wordt gebruikt, onderzoeken we de spanning tussen geografische bereikbaarheid en stedelijke leefbaarheid in Brussel. Eerst bespreken we de 150-jarige geschiedenis van het park. Vervolgens presenteren we een verkennend onderzoek naar de voorkeuren van burgers omtrent de inrichting van het park in relatie tot de aanwezigheid van gemotoriseerd verkeer. Uit dat onderzoek blijkt een sterk verband tussen de voorkeursinrichting en persoonlijke levensstijl. In de loop der jaren weerspiegelde de inrichting van het park veeleer de bredere maatschappelijke veranderingen in de manier waarop mensen hun leven organiseren, dan een concreet stadsproject. Tegenwoordig sluit de prioriteit die verschillende sociale groepen formuleren voor de inrichting van het park aan bij hun woonplaats, hun vervoerswijze en hun gebruik van en toegang tot groene ruimten. In dat kader benadrukt het onderzoek dat het noodzakelijk is om zowel concrete mobiliteitsalternatieven als nieuwe denkbeelden over mobiliteit en de stad te ontwikkelen.We explore the tensions that exist between geographical accessibility and urban liveability in Brussels, by examining the case of the Bois de la Cambre, as a place of leisure as well as transiting. First, we study the park’s 150 years of history. Second, we present an explorative survey into citizens’ preferences for the park’s set-up in relation to the presence of motorized traffic. The research reveals a strong relation between the preferred set-up and the personal way of life. Through history, the set-up of the park has reflected broader societal changes in the way people organized their life, more than it reflected an explicit urban project. Today, the priority different social groups express for the setup of the park, reflects their residential location, mode of transport, and use of and access to green spaces. In this context, the study stresses the need to work as much on the construction of concrete mobility alternatives than on the construction of new urban and mobility imaginaries