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Reference : UMR7095-KARBEN-001
Workplace : PARIS 14
Date of publication : Friday, June 4, 2021
Scientific Responsible name : Karim Benabed
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
One powerful probe of the expansion is the observation of the clustering of large structures over time. On large scales, it is possible to describe how matter is organized in the universe under the action of gravity and expansion and to deduce a history of its acceleration. To do this, dedicated observational programs have been designed, such as the DES survey, and especially the Euclid space observatory and the Rubin ground-based observatory, whose main objectives are the realization of giant surveys of galaxies in order to measure the clustering of matter on large scales, either through the biased view that their positions give, or by using coherent deformations generated by the effects of gravitational lensing of the large foreground structures. Other probes of the distribution of matter in the universe, such as the lensing effects on the cosmological background radiation or the Sunyaev Zel'dovitch effect allow to complete this vision of the acceleration of the universe.
The project proposes to set up a multi-probe co-analysis of cosmological background radiation data (mainly lensing and thermal Sunyaev Zel'dovich effect or tSZ) and galaxy catalogs (lensing, distribution). This co-analysis will be carried out on the basis of the set of 2-point correlations which contain a large part of the cosmological information. Co-analysis of these data allows to probe the evolution of the large structures of the Universe at different epochs and to be sensitive to the evolution of the expansion of the Universe and thus of the properties of the dark energy. This co-analysis also allows to be less sensitive to the instrumental or astrophysical systematics of each probe.
The state of the art in this field consists in cross-analysis of galaxy catalogs (so-called 3x2pt analysis). The extensions planned in the short and medium terms propose to add information on the lensing effect on the cosmological background radiation (we speak then of 6x2pt).
This project proposes to add the tSZ effects (10x2pt). Not only will this addition increase the constraint power of the measurement, but it should also address one of the astrophysical systematics that should limit the analyses below what the precision of the next surveys (Euclid, Rubin for the galaxies, SPT, SO and CMB-S4 for the CMB) allow to hope for. Indeed, at these levels of accuracy, it is no longer possible to consider only gravitational dynamics to model the distribution of galaxies, and it is essential to take into account the so-called 'baryonic' effects. The addition of tSZ data and a model describing them will allow to calibrate these effects. This model will be built on the basis of current knowledge and the exploitation of massive hydrodynamic simulations that include these subgrid physics effects.
This project will be developed in a new collaboration between the PhD supervisor at the Paris Institute of Astrophysics, and Elisabeth Krause at UArizona. The UArizona team is at the forefront of research in setting up 3x2pt analysis (within the DES project), and is well on its way to setting up 6x2pt analysis. The project is funded by a specific grant from the CNRS as part of the establishment of a new joint institute: the France-Arizona Institute for Global Grand Challenges.
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