PhD subjects

13 sujets IRFU

«««

• Astrophysics

A study of high energy emissions in microquasars: a spectro-polarimetric approach

SL-DSM-15-0006

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

Saclay

Contact :

Jérôme RODRIGUEZ

Starting date : 01-10-2015

Contact :

Jérôme RODRIGUEZ

CEA - DSM/IRFU/SAp/LEPCHE

01 69 08 98 08

Thesis supervisor :

Jérôme RODRIGUEZ

CEA - DSM/IRFU/SAp/LEPCHE

01 69 08 98 08

Accretion-ejection coupling in microquasars

SL-DSM-15-0131

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

Saclay

Contact :

Stéphane CORBEL

Starting date : 01-10-2014

Contact :

Stéphane CORBEL

Université Paris 7 - LEPCHE

01 69 08 45 62

Thesis supervisor :

Stéphane CORBEL

Université Paris 7 - LEPCHE

01 69 08 45 62

X-ray binairies with jets (aka microquasars) are excellent laboratories to probe the physics

in extreme environments. They consist of a "normal" companion star and a compact object

(either a neutron star or a black hole). We have, over the past years, shown that relativistic

jets are able to cary a large amount of the accretion energy. This finding has been made

possible thanks to the broad band study (much beyond the radio domain where they are

predominantly seen) of the emission of jets. Understanding these phenomena necessarily requires

multi-wavelength observations and, therefore, a large panel of tasks to perform.



Accretion is the most efficient energy source of the Universe and is seen in a large variety of celestial sources: from the early stages of star formation to active galactic nuclei. Thanks to their variability on "human" time scale (ie fraction of second to days), microquasars allow us to perform a dynamical study of the accretion-ejection coupling by observations mainly done in the X-ray and radio domains. Given the universality of the accretion-ejection, understanding microquasars, will allow a large panel of celestial objects to be understood.



The goal of the thesis is to systematically study muti-wavelength observations of a sample of microquasars mainly in the X-ray and radio domains. Spectral and temporal aspects will be investigated over the totality of their outburst. The parameters (frequency, températures, ...) will then be compared to the theoretical predictions of the models developed by the collaborators of our team.
Angular momentum evolution of solar-like stars.

SL-DSM-15-0693

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire Dynamique des Etoiles et de leur Environnement

Saclay

Contact :

Rafael A. GARCIA

Starting date : 01-10-2015

Contact :

Rafael A. GARCIA

CEA - DSM/IRFU/SAp/LDEE

0169082725

Thesis supervisor :

Rafael A. GARCIA

CEA - DSM/IRFU/SAp/LDEE

0169082725

More : http://irfu.cea.fr/Sap/index.php

More : http://irfu.cea.fr/Sap/LDEE/LDEE_web/index.html

Thanks to the asteroseismic observations provided by satellites such as CoRoT and Kepler, we are now able to probe stellar interiors, otherwise inaccessible to scientific exploitation, and thus deduce the properties of their internal structure (e.g. Bedding , ... García et al. 2011 , Nature ) and dynamics (e.g. Beck ... García et al. , 2012, Nature) . Internal rotation and magnetism have a great influence on the structure of stars and their knowledge is a key point to understand their evolution (e.g. Ceillier et al. 2012). In particular, the main sequence and red giant phase (Deheuvels et al. , 2012 and 2014 ) --where the stellar core contracts and accelerates while the outer parts expand and slow down-- are decisive steps that can now be constrained by observations. Therefore, the study of angular momentum throughout the evolution of a solar-type star has now become an observational science. The purpose of this thesis is to analyze the available data (seismic , Spectropolarimetric , etc ... ) of a large number of Kepler targets and measure the rotation from the surface to the interior. Particular attention will be paid to binary systems, to provide best reference stars at each evolutionary stage, and stars hosting planets. In a second step, the best targets will be modeled with the code STAREVOL for which the CEA is one of the poles of development (e.g. Mathis et al. 2013). With this modeling we will improve our understanding of the transport mechanisms of angular momentum in stellar interiors, as well as the role of the magnetic field in these processes. Finally, this work will be part of the preparation of the mission M3 ESA PLATO and provide valuable tools for the exploitation of this mission.



Along this thesis, the student will learn the different techniques of seismic analysis (Bayesian methods , type of Monte Carlo simulations , etc ...) and he will become familiar with different types of observations (e.g. spectroscopic and polarimetric ). In a second phase, the student will take in hand the stellar evolution code STAREVOL in collaboration with the Geneva Observatory. He will have the opportunity to use and develop one of the most complete code for the treatment of transport processes in stellar interiors.
Binary systems: formation, evolution and environment

SL-DSM-15-0070

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

Saclay

Contact :

Sylvain CHATY

Starting date : 01-10-2015

Contact :

Sylvain CHATY

Université Paris Diderot et Institut Universitaire de France - LEPCHE/Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

01 69 08 43 85

Thesis supervisor :

Sylvain CHATY

Université Paris Diderot et Institut Universitaire de France - LEPCHE/Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

01 69 08 43 85

More : http://plus.wikimonde.com/w/index.php?title=Sylvain_Chaty

More : http://irfu.cea.fr/Sap/

Massive stars live in pair...

A recent study shows that more than 70% of massive stars live in a stellar pair (Sana et al. 2012). This binarity has a major impact on the stellar evolution, strongly influenced by the presence of a "companion" star, especially via the transfer of material, angular momentum, and presence of intense stellar winds (Chaty 2013).

The fate of pairs of massive stars is determined by the evolution of each component, the most massive collapsing first in the supernova explosion, giving rise to a neutron star or a black hole (Tauris & van den Heuvel, 2006). This is the birth of a compact binary system -a compact object orbiting the companion star-, probably the most fascinating objects in the Universe. The compact object, immersed in the intense stellar wind of the massive companion star, attracts and accretes part of this wind, which accumulates on the surface, heated to temperatures of several million degrees, emitting mainly in X-rays. These celestial objects are subject to extreme variations in brightness, of several orders of magnitude on scaletime ranging from seconds to months.



... and influence their environment!

On one hand, it is now well established that the collapse of massive stars in supernova plays a key role in the enrichment of interstellar medium -from heavy atoms to complex molecules-, as well as in triggering the formation of new stars. On the other hand, the study of impact and feedback from massive stars on their environment throughout their life, has long been neglected, and remains largely unknown. However, all the material ejected through the stellar wind, and not intercepted by the compact object, is dispersed into the surrounding environment, thus colliding with a dense interstellar medium, potentially triggering new starbirth, as indicated by our recent observations with the Herschel satellite (Chaty et al. 2012 Coleiro et al. 2014).



This PhD thesis, covering many fields of Astrophysics, proposes to study the formation of pairs of massive stars, whose role is essential for the cycle of matter in galaxies, along with their evolution, and the impact on their environment, based on multi-wavelength observations.
Characterization of the youngest protostars using high angular resolution observations with the NOEMA and ALMA interferometers

SL-DSM-15-0470

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire d'étude de la Formation des Etoiles et des Planètes

Saclay

Contact :

Anaëlle MAURY

Starting date : 01-09-2015

Contact :

Anaëlle MAURY

CEA - DSM/IRFU/SAp/LFEP

0169089570

Thesis supervisor :

Anaëlle MAURY

CEA - DSM/IRFU/SAp/LFEP

0169089570

More : http://irfu.cea.fr/Pisp/anaelle.maury/

More : http://irfu.cea.fr/Projets/Calypso/

One of the main challenges to the formation of stars is the ?angular momentum problem?: the gas contained in a typical star-forming core must reduce its specific angular momentum by 5 to 10 orders of magnitude to form a typical star such as our Sun, or else centrifugal forces will soon balance gravity and prevent inflow, accretion and the growth of the protostellar embryo (Bodenheimer, 1995). Early theoretical models proposed that the formation of large (r > 100 AU) centrifugally supported disks in the protostellar cores would allow to transfer angular momentum outward and therefore solve the angular momentum problem.

Indeed, protoplanetary disks with radii 50-200 AU are routinely observed around young stars, but we still don?t know how the progenitors of these disks are formed during the earliest phases of protostellar formation. In fact, not much is known on the structure of circumstellar envelopes surrounding the youngest(Class 0) protostars at the small scales, due to a lack of observations of Class 0 objects at resolutions probing

the <100 AU scales (1'' resolution or better) in the (sub-)millimeter domain where they emit most of their energy.

Characterizing the physics at work in the inner regions of the youngest protostellar envelopes is crucial to solve the angular momentum problem, and ultimately constrain the formation and evolution models of solar-type stars (origin of the stellar initial mass function, formation of the multiple stellar systems, disks and planets).

The main objective of the proposed thesis project is to use high-angular observations of Class 0 protostars, obtained with the PdBI (CALYPSO survey), SMA and ALMA interferometers, to characterize the structure of protostellar envelopes on the small scales where disks are observed in more evolved YSOs,therefore testing if the formation of disk is indeed an outcome of, and solution to, the angular momentum problem for star formation.
Cosmological analysis of the XXL cluster survey

SL-DSM-15-0687

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Marguerite PIERRE

Starting date : 01-10-2015

Contact :

Marguerite PIERRE

CEA - DSM/IRFU/SAp/LCEG

0169083492

Thesis supervisor :

Marguerite PIERRE

CEA - DSM/IRFU/SAp/LCEG

0169083492

More : http://irfu.cea.fr/xxl

More : http://irfu.cea.fr/Sap

Clusters of galaxies are ? along with supernovae, CMB and baryonic acoustic oscillations ? are a major probe for the various cosmological scenarios. In particular, cluster number counts are very sensitive to the Dark Energy equation of state that depends on the volume (geometrical effects) and on the growth rate of the structures (gravitational effect).



The thesis will take place within the framework of the XXL project, which is the largest extragalactic survey performed by XMM (50 deg2), the X-ray satellite of the European Space Agency. The ultimate goal is toe constrain the dark energy equation of state using the some 500 clusters of galaxies newly discovered in the survey. In addition to the X-ray band, numerous observations are available in other wavebands (infrared, optical, millimetre, radio) as well as high-resolution numerical simulations. The XMM observations were performed from 2011 to 2013 and the first publications involving limited bright samples are due early 2015.



The proposed thesis work will take place during the (critical) second phase of the project and consists in a detailed study of the parameters impacting on the cosmological analysis. This regards especially the evolution of the cluster physical properties that influence their detection as well as their mass estimates. The final goal will be to adequately model these factors in the global cosmological analysis, extending the current results with 100 clusters to the complete sample of some 500 clusters.



Tools that will be used during the thesis work:

Cosmological and cluster evolutionary models; X-ray pipeline; multi-wavelength observations of clusters; results from numerical simulations. All is available and the student will have to get rapidly acquainted to them.



Working context: worldwide consortium gathering some 100 scientists and organised in well-defined sub-projects.

http://irfu.cea.fr/xxl

See page ?publications? for detailed presentations of the XXL early results at international conferences.



We are seeking excellent candidates and having a good practice of English







Explosion mechanism of core-collapse supernovae

SL-DSM-15-0790

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire de Théorie et de Modélisation

Saclay

Contact :

Thierry FOGLIZZO

Starting date : 01-09-2015

Contact :

Thierry FOGLIZZO

CEA - DSM/IRFU/SAp/LTM

01 69 08 87 20

Thesis supervisor :

Thierry FOGLIZZO

CEA - DSM/IRFU/SAp/LTM

01 69 08 87 20

More : http://irfu.cea.fr/Projets/SN2NS/

More : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=1250

Scientific context:

How do massive stars explode ?

Stars more massive than 10 Msol end their evolution with a supernova explosion which mechanism is still a theoretical mystery. Researchers would like to understand how the collapse of the iron core, accompanying the formation of a proto neutron star, is able to turn into the observed explosion. Theoretical progress over the last ten years has revealed that the spherical symmetry is broken by the development of hydrodynamical instabilities in the innermost 200km, during the second which follows the shock bounce. Those instabilities are responsible for an asymmetric explosion and the kick of the residual neutron star.

Proposed work:

This PhD work proposes to clarify the explosion mechanism by understanding the relation between the radial structure of the rotating stellar core and the asymmetric character of the explosion. The tools developed by the team at SAp for this study include analytical techniques, numerical modeling and a shallow water analogue.

Expected results:

Theoretical prediction of the explosion criterion of massive stars depending on their angular momentum and their radial structure.
Internal gravity waves: from the seismology of stars to their rotational evolution

SL-DSM-15-0592

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire Dynamique des Etoiles et de leur Environnement

Saclay

Contact :

Allan Sacha BRUN

Stéphane MATHIS

Starting date : 01-10-2015

Contact :

Allan Sacha BRUN

CEA - DSM/IRFU/SAp/LDEE

+33 1 69 08 76 60

Thesis supervisor :

Stéphane MATHIS

CEA - DSM/IRFU/SAp/LDEE

0169084930

More : http://www.stars2.eu

Our understanding of the dynamics and of the evolution of the Sun and of stars is now undergoing a revolution thanks to helio- and asteroseismology (e.g. SOHO, CoRoT, Kepler). These space missions allow us to probe their internal structure and their rotation with a very high precision. Obtained results demonstrate that the interiors of stars of different masses are the seat of a strong transport of angular momentum all along their evolution. It impacts their internal dynamics and mixing and therefore their evolution (Zahn 1992). To understand this result, it is necessary to built realistic stellar models that take into account all the magneto-hydrodynamical processes (rotation, magnetism, waves, convection and turbulence) and their non-linear interactions. In this framework, internal gravity waves (herafter IGWs), which are stochastically excited by turbulent convection, are one of the key transport mechanisms in stellar radiation zones. They also allow us to probe their structure and rotation profile when we detect them at the surface of stars thanks to seismology. IGWs are excited at the radiation/convection boundaries and they are dissipated by thermal diffusion during their propagation that allows them to carry angular momentum towards the stellar surface. Since they modify the internal rotation profile in stellar radiation zones, they also control their mixing that modifies the secular evolution of stars. They are thus one of the key mechanisms that must be studied to understand the rotational evolution of stars. Indeed, they are potentially responsible with magnetic fields for the quasi-flat uniform rotation profile of the solar radiative core and of the weak differential rotation discovered by asteroseismology in evolved stars and in intermediate-mass and massive stars (e.g. Talon & Charbonnel 2005; Fuller et al. 2014; Lee, Neiner & Mathis 2014).



A breakthrough has been obtained in the modelling of internal gravity waves thanks to 3D ASH global nonlinear numerical simulations of the Sun (Brun, Miesch & Toomre 2011; Alvan, Brun & Mathis 2014). Thanks to the simultaneous development of high-performance numerical simulations on massively parallel computers and of 3D asymptotic theories for the study of their propagation, we have been able to determine their excitation spectrum and amplitude as well as their damping. However, this study has now to be done systematically for different stellar types, particularly for all solar-type and intermediate-mass stars (from K to A types), and different evolutionary stages (e.g. Browning, Brun & Toomre 2004). Moreover, it is necessary to be able to simulate and to characterize the dynamics of internal gravity waves for all the stratification, rotation, shear, and magnetic fields possible in stars (e.g. Mathis & de Brye 2012; Mathis, Neiner & Tran Minh 2014). The key objective will be to characterize their spectrum, their amplitude, their propagation and dissipation, their visibility, and finally the angular momentum transport they induce. The obtained ab-initio models will allow us to give scaling-laws and regime-diagrams necessary for our interpretation of current and future seismic data (CoRoT & Kepler legacy and preparation of PLATO) and to get a global understanding of the dynamical evolution of stars.
Observation of Emission Line Galaxies and Quasar with the multi-spectrograph eBOSS and constraints on contraintes general relativity through redshift space distortions

SL-DSM-15-0526

Research field : Astrophysics

Location :

Service de Physique des Particules (SPP)

Groupe Bao

Saclay

Contact :

Etienne Burtin

Starting date : 01-10-2015

Contact :

Etienne Burtin

CEA - DSM/IRFU/SPP/Bao

0169085358

Thesis supervisor :

Etienne Burtin

CEA - DSM/IRFU/SPP/Bao

0169085358

More : http://irfu.cea.fr/Spp/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=2677&id_unit=8

More : https://www.sdss3.org/future/eboss.php

The evidence for the acceleration of the expansion of the Universe has triggered a wide research program aiming at identifying and understanding the phenomenon of « dark enregy ». For the last ten years, the imprint left by the baryonic acoustic oscillations (BAO) on the distribution of galaxies has been used as a « standard ruler » to measure the geometry of the universe and the cosmological parameters. Today, the community is looking towards the study of the modifications of general relativity through the study of the growth of large-scale structures. This is one of the main goals of the multi-spectrograph telescope eBOSS which will measure the redshift space distortions (RSD) for emission line galaxies and quasar in an unexplored redshift domain (0.6
Physical and statistical modelling of interstellar dust properties in the nearby universe

SL-DSM-15-0431

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Frédéric Galliano

Starting date : 01-10-2015

Contact :

Frédéric Galliano

CNRS - DSM/IRFU/SAp/LCEG

01 69 08 18 21

Thesis supervisor :

Frédéric Galliano

CNRS - DSM/IRFU/SAp/LCEG

01 69 08 18 21

Dust grains play a major role in the physics of the interstellar medium. They absorb and reemit in the infrared most of the radiated stellar power. Moreover, they are responsible for the gas heating in photodissociation regions (PDR) and serve as catalysts of numerous chemical reactions. Their properties (chemical composition, size distribution, etc.) are however currently poorly known. These uncertainties put caution on numerous aspects of our knowledge of the interstellar medium: mass estimates, PDR models, unreddening, etc. Refining our comprehension of dust is crucial to understand the life cycle of interstellar matter and its effect on galaxy evolution.

One of the approaches, to tackle these open questions, consists in studying the way the observed grain properties vary with the physical conditions they experience. The PhD thesis we propose is aimed at focussing on the properties of the smallest grains (with a radius smaller than ?10 nm) and of polycyclic aromatic hydrocarbons (PAH). These interstellar medium components radiates out of equilibrium in the mid-infrared (?5-40 µm), and are the carriers of numerous resonance bands. This study will focus on several nearby galaxies, including the Magellanic clouds. The interest of studying nearby galaxies rather than the interstellar medium of our own galaxy resides in the diversity of the physical conditions of the environments we can access (metallicity, stellar radiation field intensity, etc.).

Numerous studies have already been published on this subject. However, most of them were superficial. There remains many aspects to study: identifying and physically modeling several bands of solids in star forming regions, and the correlation of the properties of the main PAH bands with the physical conditions diagnosed thanks to the new Herschel data.

The thesis will have several aspects. First, the analysis of mid-infrared spectra, obtained with the satellite Spitzer. Most of these spectra are already reduced. Most of this first step will consist in critically selecting the spectra to study, and homogenizing the data. Then, quantifying the physical components, which is not trivial, will be performed in a sophisticated manner. We propose that the student will develop a hierarchical bayesian model for spectral decomposition, which will allow him a precise quantification of the uncertainties and of the correlations between physical parameters. This new tools and its meticulous application to the data is the guaranty of a precise and original interpretation of the physical processes in the studied regions.

This thematics is particularly relevant for planning the scientific objectives of the James Webb Space Telescope (JWST), which should be launched in 2018.

Supernova remnants with Fermi, CTA, and the cosmic ray origin

SL-DSM-15-0337

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

Saclay

Contact :

Jean BALLET

Thierry STOLARCZYK

Starting date : 01-09-2015

Contact :

Jean BALLET

CEA - DSM/IRFU/SAp/LEPCHE

01 69 08 70 17

Thesis supervisor :

Thierry STOLARCZYK

CEA - DSM/IRFU/SAp/LEPCHE

+33 1 69 08 78 12

More : http://irfu.cea.fr/Sap/

More : http://fermi.gsfc.nasa.gov/ssc/

The goal of the PhD is the study of supernova remnants with gamma rays, trying to pin down the acceleration sites of high energy cosmic rays. The study will be essentially based on observations by the Fermi satellite (covering the energy range 30 MeV-300 GeV). The results obtained shall contribute to the scientific program of CTA, an observatory in its prototyping phase covering energies from 50 GeV to beyond 10 TeV, expected to improve the sensitivity of the current Cherenkov instruments by a factor of ten. Several aspects will be explored:



? Spectral modelling of a few bright supernova remnants detected by Fermi and by Cherenkov telescopes, in the light of radio and X-ray observations;

? Participating in building the Fermi catalogue of supernova remnants at GeV energies;

? Developing a population model for galactic supernova remnants in the GeV-TeV energy range on the basis of theoretical expectations;

? Applying this population model to predict the discovery potential of CTA in a semi-quantitative way, and developing candidate selection criteria for detailed CTA observations.

The growth of black holes and stellar mass in galaxies through cosmic time

SL-DSM-15-0502

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Emanuele DADDI

Starting date : 01-10-2015

Contact :

Emanuele DADDI

CEA - DSM/IRFU/SAp/LCEG

Thesis supervisor :

Emanuele DADDI

CEA - DSM/IRFU/SAp/LCEG

observations in the local Universe have established that galaxies contain supermassive black holes with masses that are

about 1/1000th of the host galaxy. It is still unclear which mechanism is at the origin of this correlation, inducing

such a fine tuning of masses at so different spatial scales. This thesis will use observations at a variety of wavelengths

of galaxies at high redshifts to explore the co-existence of stellar mass growth (via star formation) and black hole growth

(via black hole accretion), and thus constrain related key physical processes at the time the correlation was put in place.

The distribution of star formation in galaxies through cosmic time is remarkably simple and well behaved, as shown by the

existence of tight relations between fundamental galaxy parameters like stellar masses, star formation and molecular hydrogen

content. On the other hand, when considering individual galaxies, the black hole accretion rate (as proved by X-ray luminosities)

does not correlate with any other galaxy properties. When instead considering large galaxy ensembles, our group

was first to show that correlations are present with stellar masses. The thesis project will expand the work along these lines,

in particular using mid-IR probes of black hole growth together with X-ray to include the most obscured phases which are still

unaccounted for, based on new ultra-deep IR catalogs with Herschel, Spitzer and submm facilities. We will explore if the ensemble

black hole to stellar mass ratio depend on key physical parameters like morphology, star formation mode (merging or quiescent),

and redshift, shedding light on the co-evolution (or lack there-of) of black holes and galaxies.

The work will be carried out using the deepest Herschel data which are available to us, publicly available facilities,

and proposing for telescope time for crucial missing ingredients. In addition, the candidate will be able to work

with deep ground based and space based spectroscopy to study high redshift galaxy emission lines. The candidate will gain the

necessary scientific and technical expertise to be able to competitively request telescope time with major forthcoming facilities

like the Atacama Large Millimeter Array and the new generation optical-mid-IR space telescope (JWST).

Weak gravitational lensing: measurement of galaxy shapes and cosmological parameters

SL-DSM-15-0061

Research field : Astrophysics

Location :

Service d'Astrophysique (SAp)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Martin Kilbinger

Starting date : 01-10-2015

Contact :

Martin Kilbinger

CEA - DSM/IRFU/SAp/LCS

01 69 08 17 53

Thesis supervisor :

Martin Kilbinger

CEA - DSM/IRFU/SAp/LCS

01 69 08 17 53

More : http://cosmostat.org/kilbinger

More : http://cosmostat.org

Weak gravitational lensing, the distortion of the images of high-redshift

galaxies due to the presence of matter inhomogeneities on large scales in the

Universe, is thought to be one of the most promising tools of cosmology to

constrain models of dark matter and dark energy. The planned space mission

Euclid will map 15000 square degrees of extragalactic sky to measure

weak-lensing distortions from a billion galaxies. The distortions induced by

matter in the Universe are an order of magnitude smaller than the intrinsic

shape distribution of such galaxies. Furthermore, the galaxy images are blurred

by the PSF (point-spread function) of the optical imaging system. The

correction of the PSF has to be performed at the percent level accuracy. One of

the major challenges for weak lensing is the accurate measurement of the shapes

of faint, high-redshift galaxies. The subject of this thesis is to explore

methods of galaxy shape measurement, to determine their errors, and to

propagate this information to cosmological parameters.

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