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Journ´ees “Math´ematiques et Cosmologie” 2012

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Journ´ ees “Math´ ematiques et Cosmologie” 2012

Lieu et dates

Universit´e Lille 1, 19 juin et 22 juin 2012.

Pr´esentation

Cette manifestation a comme but de faire connaˆıtre `a la communaut´e math´ematique des probl`emes qu’int´eressent les cosmologistes. Pour cela une s´erie d’expos´es aura lieu `a l’Univer- sit´e Lille 1. Les orateurs sont un groupe de scientifiques d’Estonie et d’Espagne qui travaillent ensemble depuis plus de 20 ans.

Parmi les membres de ce groupe, Enn Saar et V. J. Martinez ont ´ecrit un livre intitul´e “Sta- tistics of the Galaxy Distribution” (Chapmann and Hall, 2002).

Organisateurs

Youri Davydov, Radu S. Stoica et Alain Vienne Contact e-mail : radu.stoica@math.univ-lille1.fr Programme

Mardi 19 juin :Salle de s´eminaire du bˆatiment M3

•10h30 - 11h30 : Estimating cosmological correlations (E. Saar)

•14h00 - 14h30 : Multimodality of galaxy clusters from the SDSS DR8 within the supercluster- void network (M. Einasto)

•14h30 - 15h00 : pause caf´e

•15h00 - 15h30 : Orientation of galaxies in filaments : 3D photometrical modelling of galaxies and filamentary structure in the SDSS (E. Tempel)

Vendredi 22 juin :Salle de r´eunion du bˆatiment M2. Cette pr´esentation rejoint le cadre du Colloquim organis´e par le Laboratoire Paul Painlev´e.

•11h15 - 12h15 : Detecting subtle structures in the galaxy distribution using wavelets (V. J.

Martinez)

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R´esum´es des expos´es

Estimating cosmological correlations (E. Saar)

I will give an overview of estimating correlation functions of cosmological galaxy distributions.

I will describe the error sources (discreteness, cosmic noise) and ways to handle these. I will present in detail a novel method for estimating discreteness errors by block bootstrap.

Multimodality of galaxy clusters from the SDSS DR8 within the supercluster-void network (M.

Einasto)

We study the relations between the multimodality of galaxy clusters drawn from the SDSS DR8 and the environment where they reside. We apply a number of 3D, 2D, and 1D tests to find signatures of multimodality of galaxy clusters, and test our results with Monte Carlo simulations. We use the luminosity density field to study the environmental densities around clusters, and to detect superclusters where clusters reside. We determine the morphology of superclusters with the Minkowski functionals and compare the properties of clusters in su- perclusters of different morphology. We find that more than 80% of clusters show signatures of multimodality : the presence of substructure and/or non-Gaussian velocity distributions.

Multimodal clusters reside in a higher density environment than unimodal clusters. Super- clusters can be divided into two main morphological types, spiders and filaments. Clusters in superclusters of spider morphology have higher probabilities to have substructure and larger peculiar velocities of their main galaxies than clusters in superclusters of filament morphology.

Our study shows the importance of the role of superclusters as a high density environment that affects the properties of galaxy systems in them.

Orientation of galaxies in filaments : 3D photometrical modelling of galaxies and filamentary structure in the SDSS (E. Tempel)

We search for and find evidence that the spin axes of galaxies relative to their host filaments are not randomly distributed. Similarly to dark matter haloes in N-body simulations, spin axes of spiral galaxies are weakly aligned parallel to filaments, whereas elliptical galaxies have orthogonal alignment. To find the spin axes of galaxies, we used the 3D photometrical model of galaxies. This model allows to estimate relatively accurately the inclination angle of ga- laxies, whereas in 2D models the inclination angle is degenerate with the disc thickness. To search for filaments in the cosmic web, we use a three-dimensional object point process, which help to find the filaments and also defines the orientation of a filament. In my talk, firstly, I describe the 3D photometrical model of galaxies and how accurately it restores the structural parameters and inclination angles of galaxies. Secondly, I describe the method that we used to find filaments and I demonstrate how good are the detected filaments. Finally, I combine these two results and search for correlation between filaments and spin axes of galaxies.

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Detecting subtle structures in the galaxy distribution using wavelets (V. J. Martinez)

In this talk I will present a novel and successful technique to detect very elusive cosmic struc- tures in the large scale distribution of galaxies. By means of a specially designed wavelet we are able to unveil the baryon acoustic structures, which are fossils of the early universe physics.

These features are shells of radius 150 Mpc, with density slightly higher than the average, surrounding central regions of high density. The novelty of our approach relies on using an appropriate wavelet function acting directly on the density field. We have identified, for the first time, some of these individual cosmic structures and have reconstructed its shape and scale. This results allows the study of the geometry of the universe.

Institutions partenaires

Universit´e Lille 1, Laboratoire Paul Painlev´e, Laboratoire d’Astronomie de Lille - IMCCE Observatoire de Tartu - Estonie, Observatoire Astronomique et l’Universit´e de Val`encia - Es- pagne

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