3 sujets /DAp/LCS

Dernière mise à jour : 11-08-2022


 

Cross-correlating Euclid and DESI to probe the dark-matter - baryon connection in the cosmic web using weak gravitational lensing

SL-DRF-22-0483

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Martin Kilbinger

Starting date : 01-10-2022

Contact :

Martin Kilbinger
CEA - DRF/IRFU/DAP/LCS

21753

Thesis supervisor :

Martin Kilbinger
CEA - DRF/IRFU/DAP/LCS

21753

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

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

Weak gravitational lensing, the distortion of images of high-redshift galaxies due to foreground matter structures on large scales, is one of the most promising tools of cosmology to map the dark-matter distribution in the Universe. By combining weak lensing observations with foreground galaxy samples, we can measure the connection between dark matter and baryonic mass in galaxies. The lensing - galaxy cross-correlation is one of the main blocks in modern cosmology. It is an ingredient to test a variety of models of modified gravity, in which photons from weak lensing and galaxies experience different gravitational potentials. It further allows to measure two of the most important astrophysical uncertainties in cosmology, the intrinsic alignments of galaxies and galaxy bias.

The goal of this PhD thesis is to measure cross-correlations between weak lensing and galaxies, using the upcoming Euclid and DESI surveys. In preparation, existing weak-lensing data will be used from UNIONS, an ongoing imaging survey covering 3,600 square degree to date. This data will be cross-correlated with existing BOSS/eBOSS spectroscopic galaxies. This work aims toward a better understanding of the dark-matter – baryon connection, which will not only help to improve cosmological analyses, but also deepen our knowledge of how galaxies formed in their dark-matter environments in the early Universe.

Cosmology from LiteBIRD and synergy with large-scale surveys like Euclid

SL-DRF-22-0485

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Valeria Pettorino

Starting date : 01-10-2022

Contact :

Valeria Pettorino
CEA - DRF/IRFU/DAP/LCS


Thesis supervisor :

Valeria Pettorino
CEA - DRF/IRFU/DAP/LCS


Personal web page : https://www.cosmostat.org/people/valeria-pettorino

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

More : https://www.valeriapettorino.com/

This PhD proposal is meant to combine information from galaxy surveys like the forthcoming Euclid space mission and Cosmic Microwave Background Experiments from ground and space.

The Cosmic Microwave Background radiation has demonstrated to be a powerful probe for cosmology: its temperature anisotropies carry information on the early-time Universe, as well as on the structure encountered along the light path. Measurements from balloons and detectors from ground are contributing to detail this picture with current data from Planck space mission, and forthcoming data from ground, balloons, and space.

Within galaxy surveys, ESA Euclid satellite , to be launched in 2023, will observe how galaxies formed to study the nature of dark energy and dark matter.

The PhD project is co-supervised by Valeria Pettorino (CEA/DRF/IRFU/DAp/LCS) and Dr. Stéphane Ilic (IJLAB, Orsay). We have identified three main goals:

1. contribute to the estimation of the scientific impact of LiteBIRD CMB space mission via forecasts;

2. contribute to the synergy between CMB experiments and Euclid within the Euclid likelihood development;

3. investigate different methods to separate foreground components and improve the reconstruction of the CMB signal.

Likelihood-free cosmological parameter inference using theoretical high-order statistics predictions

SL-DRF-22-0405

Research field : Numerical simulation
Location :

Direction d’Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Jean-Luc STARCK

Starting date : 01-10-2022

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 2023, 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. Cosmological parameters are traditionally estimated using a Gaussian likelihood based on theoretical predictions of second order statistic such as the power spectrum or the two point correlation functions. This requires to build a covariance matrices, and therefore need a lot of very heavy n-body simulations. This approach presents also several additional drawbacks: First, second order statistics captures all available information in the data only in the case of Gaussian Random Fields, while matter distribution is highly non-Gaussian showing many features such filaments, walls or clusters. Second, the covariance matrix is cosmology dependent and the noise it generally not Gaussian, both aspects being generally poorly taken into account. Finally, all systematic effects such as masks, intrinsic alignement, baryonic feedback are very difficult to take into account. For all these reasons, a new approach has recently emerged, called likelihood-free cosmological parameter inference which are based on a forward modelling. It has the great advantage to not need covariance matrices anymore, avoiding the storage of huge simulated data set (we typically need 10000 n-body realisations for each set of cosmological parameters). Furthermore, it opens us the door to use high order statistical information and it is relatively straightforward to include all systematics effect. It has however two serious drawbacks, the firsts one is the need of huge GPU ressources to process surveys such as Euclid and the second is that the solution relies on the accuracy of simulations, which could lead to infinite discussion in case the results are different from what is expected. Thanks to a recent breakthrough (Codis, 2021), we have now theoretical tools to predict, for a given set of cosmological parameters, the multi-scale density probability function (pdf) of convergence maps such as the one that will be observed with Euclid.

The goal of this PhD work is to develop an hybrid approach, consisting in a likelihood-free cosmological parameter inference which would be based on the high order statics theoretical prediction rather than n-body simulations. It would therefore have the advantage of both previously described approaches, as it will not need to store huge data set to compute a covariance matrix and it will not require huge CPU/GPU ressources as the forward modelling method. This intense frugality will make this approach highly competitive to constraint the cosmological model using high order statistics in future surveys.

To achieve this goal, the first step will be to build a map emulator, similar to what has been done for 2 point statistics (i.e. the flask method), but which respects accurately the high order predictions. Using this emulator, it will then be possible to use it as a bypass in a recently developed Likelihood Free Inference code. This will allow the use of high order statics such as the l1-norm of the wavelet transform of the convergence to constrain the cosmological parameters, which is an extremely powerful summary statistic (Ajani et al, 2021). The developed method will be used first on the CFIS survey and then on Euclid.



References

Barthelemy A., Codis S. and Bernardeau F., "Probability distribution function of the aperture mass field with large deviation theory", 2021, MNRAS, 503, 5204;

V. Ajani, J.-L. Starck and V. Pettorino, "Starlet l1-norm for weak lensing cosmology", Astronomy and Astrophysics,  645, L11, 2021.

 

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