9 sujets IRFU/DAp

Dernière mise à jour : 13-12-2018


• Astroparticles

• Astrophysics

• Mathematics - Numerical analysis - Simulation

 

Cosmology with gravitational waves and galaxy clustering: synergie between LISA and Euclid

SL-DRF-19-0429

Research field : Astroparticles
Location :

Direction d'Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Martin Kilbinger

Starting date : 01-10-2019

Contact :

Martin Kilbinger

CEA - DRF/Irfu/SAp/LCS

01 69 08 17 53

Thesis supervisor :

Martin Kilbinger

CEA - DRF/Irfu/SAp/LCS

01 69 08 17 53

Personal web page : http://www.cosmostat.org/people/kilbinger

Laboratory link : http://www.cosmostat.org

The goal of this thesis is to explore the potential of gravitational waves (GWs) at cosmological distance as standard sirens to measure the expansion history of the Universe. Since most GWs from merging black holes are not expected to have an electro-magnetic counterpart, we need to estimate the redshift of the GWs host galaxy statistically. For this, we propose to use galaxy clustering from wide and deep photometric galaxy surveys. The same data will be used to reduce the weak-lensing magnification contamination of the GW luminosity distance.



To analyse the GW Hubble diagram, we aim to understand and model the uncertainty in the luminosity distance (signal generation and propagation), the redshift uncertainty (using photometric and clustering redshifts, and machine learning), and parameter inference, for which we will use forward-modelling and likelihood-free methods to account for the non-Gaussianity of the data.

Dark interstellar gas and Fermi Bubbles

SL-DRF-19-0264

Research field : Astrophysics
Location :

Direction d'Astrophysique (DAP)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Isabelle GRENIER

Starting date : 01-09-2019

Contact :

Isabelle GRENIER

Université Paris Diderot - DSM/IRFU/SAp/LEPCHE

01 69 08 44 00

Thesis supervisor :

Isabelle GRENIER

Université Paris Diderot - DSM/IRFU/SAp/LEPCHE

01 69 08 44 00

Personal web page : https://www.nasa.gov/mission_pages/GLAST/team/bio_grenier.html

Laboratory link : irfu.cea.fr/dap/

Because of the lack of emission, large quantities of gas escape from the inventory of the interstellar medium [1]. This dark gas is concentrated at the interface between the atomic and molecular phases of clouds. It plays a decisive role in the interstellar cycle and it informs us on the capacity of the large gas reservoirs of galaxies to produce molecular clouds to form stars. Yet, we know hardly anything about the composition, state, and abundance of the dark gas, or how these properties vary across a galaxy. Finding direct means of observation and characterising this interstellar phase are therefore two major objectives for understanding galactic ecosystems.

The dark gas is indirectly revealed by coupling observations of the dust that it contains and of the cosmic rays that diffuse in it and radiate in gamma rays. The proposed goal for the thesis is to exploit the Fermi gamma-ray data and the data from multiple interstellar surveys (Planck, WMAP, Gaia, new radio and mm surveys) to study the largest dark-gas complex in the solar neighbourhood. The analyses will allow to quantify the content of visible and dark gas in the clouds, to follow the penetration of cosmic rays in the dense phases, and to characterise the evolution of the dust properties across the gas phases. This last point is essential to pave the way for reliable Galactic and extragalactic studies of the dark gas exploiting only dust radiation.

The study will face the challenge of separating the interstellar gamma-ray emission from that of the Fermi Bubbles (large jets of high-energy particles expelled from the central regions of the Galaxy) by developing a multispectral component separation method.

The student will also be able to participate in the CNES co-PILOT sub-millimetre balloon project that is planned for 2020 to look for C+ recombination signatures in the local dark gas.

The work will be carried out within the Fermi International Collaboration and will benefit from numerous exchanges with interstellar experts in France (at ENS and IRAM), the United States (Alma, Stanford), Australia (SKA-GASKAP), and China (FAST). The student will participate at the beginning of the thesis in the month-long international workshop to be held on dark gas at the Pascal Institute of Paris-Saclay University.

[1] Grenier et al., 2005, Science 307, 1292

A search for gamma ray bursts with CTA

SL-DRF-19-0326

Research field : Astrophysics
Location :

Direction d'Astrophysique (DAP)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Thierry STOLARCZYK

Starting date : 01-09-2019

Contact :

Thierry STOLARCZYK

CEA - DRF/IRFU/DAp/LEPCHE

+33 1 69 08 78 12

Thesis supervisor :

Thierry STOLARCZYK

CEA - DRF/IRFU/DAp/LEPCHE

+33 1 69 08 78 12

Personal web page : http://irfu.cea.fr/Pisp/thierry.stolarczyk/

Laboratory link : http://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3709

More : https://www.cta-observatory.org/

The CTA observatory is a next-generation ground-based instrument for exploring the sky in gamma rays at very high energies, with a sensitivity ten times better than the existing and an amazing new capacity for the search of transient source counterparts.

The objective of the PhD is the study of the influence of the extragalactic background light on the detectability of the gamma ray bursts in CTA, and to optimise the real-time search strategy for gamma ray bursts and gravitational wave counterparts.

The research will contribute to the development of the data pipeline and the data analysis tools using the first observatory data.

Study and characterization of the polarimetric bolometers of the B-BOP instrument on SPICA Space Observatory.

SL-DRF-19-0575

Research field : Astrophysics
Location :

Direction d'Astrophysique (DAP)

Laboratoire des spectro-Imageurs spatiaux (LSIS)

Saclay

Contact :

Vincent REVERET

Louis RODRIGUEZ

Starting date : 01-10-2019

Contact :

Vincent REVERET

CEA - DSM/IRFU/SAp/LSIS

01 69 08 74 02

Thesis supervisor :

Louis RODRIGUEZ

CEA - DRF/IRFU/DAP/LSIS

0169086948

Laboratory link : http://irfu.cea.fr/dap/

The Herschel submillimeter space observatory has revolutionized some areas of astrophysics, such as star formation, showing that stars are formed mainly in filaments of gas and dust. This rises a fundamental question on the role of the magnetic field within these structures that cannot be solved by the current astrophysical instruments. The B-BOP instrument, installed on the future SPICA international space observatory and proposed by CEA Saclay, will be able to detect a wide variety of far-infrared filaments, as well as their possible associated magnetic field (through the polarization of the light coming from these regions).

B-BOP will contain 3 focal planes of cryogenic silicon bolometers currently developed by CEA (LETI and Saclay). These are very innovative detectors, operating at 50 mK, with a very high sensitivity. Each pixel is intrinsically sensitive to the polarization of incident radiation.

For this thesis, the first step will be to model, and test the bolometers of Safari-Pol (measurement of sensitivity, time constant, cross-polarization, etc ...). This work will require the development of dedicated state-of-the-art instrumentation (very low flux optical sources, ultra low temperature cryostat). The results obtained will then be discussed in the more general framework of the instrument's preparation, in particular concerning its calibration, the estimation of its performance in space, as well as the optimization of future observation modes.

Definition of the neutron environment in the Earth's atmosphere

SL-DRF-19-0619

Research field : Astrophysics
Location :

Direction d'Astrophysique (DAP)

Laboratoire des spectro-Imageurs spatiaux (LISIS)

Saclay

Contact :

Arnaud CLARET

Sébastien BOURDARIE

Starting date : 01-10-2019

Contact :

Arnaud CLARET

CEA - DRF/IRFU/DAP/LISIS

0169083762

Thesis supervisor :

Sébastien BOURDARIE

ONERA - DPHY/ERS

0562252756

The knowledge of the Earth's natural radiative natural environment (NRE) and its dynamics is an important issue for controlling the risks of malfunctioning of advanced technologies, dosimetric risks (biological effects), and in assessing the impact of albedo neutrons escaping from the upper atmosphere to the radiation belts. The latter contribute on the one hand to the population of the proton radiation belt (Salammbô models) and on the other hand induce instrumental background noise on all equipment operated in low or high altitude orbit, including in particular instruments dedicated to astronomy or to the study of the globe. For their part, cosmic rays (essentially composed of protons and helium nuclei) interact with atoms in the upper atmosphere either by losing part of their energy through ionization or for the most energetic particles, by causing nuclear reactions. These secondary reactions in turn cause cascade reactions and up to ground level, the result being the generation of secondary particles of the neutron, proton, electron or muon type, whose spectra will vary according to altitude, longitude, latitude, atmospheric conditions and solar activity.



The objective of this thesis is to characterize secondary particles of atmospheric RNE from adapted nuclear transport codes (GEANT4, MCNPx, FLUKA or Corsika) based on a 3D model of the atmosphere. In addition, this 3D approach will allow to characterize the angular distribution of secondary particles and quantify the components escaping from the upper atmosphere to the radiation belts. The impact of cosmic radiation modulation as a function of the solar cycle on the population of atmospheric neutrons and albedo will be quantified. The model results will be validated with the neutron spectrum measurements performed by ONERA/DPHY at Concordia (Antarctica). In addition to its high neutron detection level (altitude 3223m, cut-off rigidity ~ 0GV), this measurement site is characterized by a scene that can be easily modelled thanks to its stable water conditions. Additional comparisons may be made from other spectrometers and/or instruments (neutron monitors). The model results will also be compared with instrumental background noise measurements from several space missions. In the long term, this model could be extended to study the impact of solar flares on their contributions to neutron generation in the Earth's atmosphere and its albedo component (SPAND). Another perspective will be to apply this cosmic shower modeling to the case of Jupiter, whose atmospheric and magnetic conditions are very different from the terrestrial case.



The bibliographic work will cover the fields of cosmic rays, atmospheric modelling and radiation-matter interactions (cosmic showers). An important task will be to orient the choice of a nuclear transport tool (GEANT4, MCNPx, FLUKA or Corsika) according to the problem and the relevance of the physical models. The thesis work will be divided into several steps:



1) Development of a 3D model of the atmosphere (latitude, longitude and altitude) based on the state of the art.



2) Characterization of secondary particles of atmospheric RNE from adapted nuclear transport codes based on the 3D model of the atmosphere (angular properties of secondary particles integrating the component escaping from the upper atmosphere to the radiation belts). [1]



3) Validation of 3D modelling with neutron spectrum measurements performed by ONERA/DPhIEE at Concordia (Antarctica). Additional comparisons may be made from other spectrometers and/or instruments (neutron monitors). [2]



4) Valuation of this new physical description in the "Salammbô 3D" and "MUSCA SEP3" themes. [3]



5) Assessment of expected background noise in low orbit for different space missions and comparison with flight data (ESA/Integral for gamma albedo, JAXA/Hitomi for neutron albedo); application to space missions in preparation (CAS/Einstein Probe, ESA/Theseus).



References

[1] Natacha Combier, Arnaud Claret, Philippe Laurent, Vincent Maget, Daniel Boscher, Alfredo Ferrari, and Markus Brugger, "Improvements of FLUKA Calculation of the Neutron Albedo", IEEE Transaction on Nuclear Science, VoL. 64, NO. 1, January 2017.

[2] G. Hubert and A. Cheminet, "Radiation effects investigations based on atmospheric radiation model (ATMORAD) considering GEANT4 simulations of extensive air showers and solar modulation potential", Radiation Research, Vol. 184, No. 1, pp. 83-94, July 2015.

[3] G. Hubert, S. Duzellier, C. Inguimbert, C. Boatella-Polo, F. Bezerra, and R. Ecoffet, "Operational SER calculations on the SAC-C orbit using the Multi SCAles Single Event Phenomena Predictive Platform (MUSCA SEP3)", IEEE Trans. Nucl. Sci., Vol. 56, No.6, pp. 3032-3042, Dec. 2009.

Development of an adaptive mesh refinement code for the exascale area and astrophysical applications

SL-DRF-19-0501

Research field : Astrophysics
Location :

Direction d'Astrophysique (DAP)

Laboratoire de modélisation des plasmas astrophysiques (LMPA)

Saclay

Contact :

Patrick Hennebelle

Starting date : 01-09-2019

Contact :

Patrick Hennebelle

CEA - DSM/IRFU/SAp

0169089987

Thesis supervisor :

Patrick Hennebelle

CEA - DSM/IRFU/SAp

0169089987

The role of gas and star formation inside the first forming galaxy structures

SL-DRF-19-0046

Research field : Astrophysics
Location :

Direction d'Astrophysique (DAP)

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

Saclay

Contact :

Emanuele DADDI

Starting date : 01-10-2018

Contact :

Emanuele DADDI

CEA - DRF/IRFU/SAp

Thesis supervisor :

Emanuele DADDI

CEA - DRF/IRFU/SAp

At redshifts of z=2 to 3, the epoch of the peak star formation and black hole activity in the Universe, the first giant dark matter halos were also growing very rapidly, and baryons falling into their deep potential wells induced prodigiously vigorous activity leading to the major phases of galaxy and black hole assembly, often hidden by dust. These early phases for the evolution of galaxies are expected to be crucial to lead to the formation of their dominant early type galaxy population (via quenching mechanisms still poorly understood) and well relaxed hot gas atmospheres, as observed in local massive galaxy clusters (via some sort of yet unknown feedback between galaxies and the hot gas, leading to energy and entropy injection affecting its thermodynamic evolution). The overall physical processes relevant for galaxies and structures evolution in the first forming clusters are still largely poorly mapped, and yet not well understood. But increasing interest and efforts in the community coupled with emerging observational results and prospects for future mission (e.g., JWST, Euclid and Athena) make this research field one of the most hot and promising in the current domain of galaxies and structure formation. I propose a PhD thesis in Saclay in this research field, based on new observations with ALMA, NOEMA, Herschel, HST and Keck of two dense structures discovered by our research groups at z=2 and 2.5 (Gobat et al 2011; 2013; Wang et al 2016) and a new forming cluster found at z=2.91. The student will be responsible of the final reduction, analysis and interpretation of a substantial amount of data we obtained

with the new and revolutionary Keck Cosmic Web Imager, allowing for the first time 3D spectroscopy in the blue over large fields, down to wavelengths not accessible to the MUSE instrument at the VLT. These Keck data have revealed giant clouds of cold gas extending over 100kpc or more at the cluster cores, detected from their Lya emission. The high level goal of the thesis will be to observationally characterise and understand the nature, origin and fate of these giant reservoirs of cold gas. This will be done in particular in connection with galaxy activity present in the clusters, that will be probed by HST multicolour imaging (to reveal morphologies, stellar populations and merging rates possibly connected to galaxy stripping and production of inter cluster material) and with NOEMA, ALMA and Herschel (to study gas reservoirs, star formation hidden by dust and the state of the interstellar medium). The cold gas might eventually result to be a first convincing smoking gun of cold flow accretion to massive dark matter halos required by theory to justify the vigorous galaxy activity present at high redshift. Such smoking gun has long been sought observationally at high redshifts but never convincingly detected yet. Possible evidences leading to this could be connected with the morphology of the Lya gas, large kinematics and metal enrichment, that we will be able to investigate with existing data and with future observations. The student will be, in fact, involved during the PhD in a vigorous effort of proposing for Keck, VLT and ALMA/NOEMA time, to foster this science, with a resulting expertise in all aspects of observational astronomy, including experience with dealing with truly multi-wavelength datasets.

The environments giving birth to long Gamma Ray Bursts: preparing the SVOM science

SL-DRF-19-0281

Research field : Astrophysics
Location :

Direction d'Astrophysique (DAP)

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

Saclay

Contact :

EMERIC LE FLOC'H

Starting date : 01-10-2019

Contact :

EMERIC LE FLOC'H

CEA - DSM/IRFU/SAp/LCEG

0169088235

Thesis supervisor :

EMERIC LE FLOC'H

CEA - DSM/IRFU/SAp/LCEG

0169088235

Personal web page : http://irfu.cea.fr/Pisp/emeric.le-floch/

Laboratory link : http://irfu.cea.fr/dap/en/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=977

Gamma-Ray Bursts originating from the death of massive stars represent an ideal tool for probing the early Universe and star formation within distant galaxies. However, many questions are still opened on the nature of environments favoring the occurrence of such phenomena, in particular on the differences they show with respect to the entire population of galaxies responsible for star formation throughout cosmic history. We will shed a new light on these questions, thanks to the analysis of high resolution observations of high redshift gamma-ray burst host galaxies obtained on one hand in the near-infrared with the Hubble Space Telescope, and on the other hand with the ALMA millimeter interferometer operating in Chile. These data will allow us constraining the morphology of these galaxies, their star formation surface density, as well as their dust and molecular gas content. Besides, we will infer predictions on the distribution of extinctions in the interstellar medium of distant galaxies such as what will be systematically measured with the gamma-ray bursts to be detected with the future SVOM satellite. This PhD project is proposed in the context of the advent of "time-domain astrophysics" expected for the next decade, and will enable in particular a better assessment of the use of gamma-ray bursts as tracers of massive stars at the scale of cosmological structures.

Optimal Transport and Deep Learning to model the Euclid Point Spread Function

SL-DRF-19-0010

Research field : Mathematics - Numerical analysis - Simulation
Location :

Direction d'Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Jean-Luc STARCK

Starting date : 01-10-2019

Contact :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

Thesis supervisor :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

Personal web page : http://jstarck.cosmostat.org

Laboratory link : http://www.cosmostat.org

The Euclid satellite, to be launched in 2022, will observe the sky in the optical and infrared, and will be able to map large scale structures and weak lensing distortions out to high redshifts. Weak gravitational lensing is thought to be one of the most promising tools of cosmology to constrain models. Weak lensing probes the evolution of dark-matter structures and can help distinguish between dark energy and models of modified gravity. Thanks to the shear measurements, we will be able to reconstruct a dark matter mass map of 15000 square degrees. These shear measurements are derived from the galaxy shapes, which are blurred by the PSF (point-spread function) of the optical imaging system. One of the main problems to achieve the scientific goals is therefore the need to model the point spread function (PSF) of the instrument with a very high accuracy. The PSF field can be estimated from the stars contained in the acquired images. It has to take into account the spatial and spectral variation of the PSF. An additional problem to take care of is the subsampling of the images. Once the PSF is correctly modelled, we need to derive the shear from galaxy shapes.

In a recent paper (Schmitz et al 2018) we shown that optimal transport (OT) techniques allow to extremely well represent the evolution of the PSF with the wavelength and on-going work (Morgan et al, 2018) consists in building a 3D Euclid PSF modelling, which takes into account both the spatial variation of the PSF and the PSF wavelength dependency. However even if OT produces beautiful results, its use is extremely limited in practice due to a prohibitive computational cost, and we cannot consider to use our OT PSF modeling for the huge Euclid set.

The goal of the PhD consists first in finding an efficient way to build such a 3D PSF model. A solution could be to use the Deep Wasserstein Embedding technique (Courty, Flamary and Ducoffe, 2017) to get an approximation mechanism that allows to break the complexity. The second step will be to interpolate, from the reconstructed 3D PSFs at stars position, the PSF at any position in the field. This will done by extending to the third dimension the 2D interpolation on a Graph Laplacian we proposed in (Schmitz, Starck and Ngole, 2018), which allows us to interpolate the PSF on the adequate manifold. The final step will be to quantify the modelling errors by studying using simulations the propagation of the reconstructed PSFs errors to cosmological parameters.

 

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