Euclid : Estimation of the mass of the clusters of galaxies using weak lensing convergence maps (4-6 months)

Full description

Clusters of galaxies are the largest and most massive collapsed structures in the Universe. Their content reflects that of the Universe : 85% of dark matter and only 15% of ordinary matter in the galaxies and the inter-galactic gas. Clusters contain valuable information on cosmology, and are particularly important for dark matter studies. Weak Lensing is the process in which light from background galaxies is bent by foreground objects (i.e cluster of galaxies) as it travels toward us. The resulting distorsions in the shape of background galaxies provides a direct way to probe the total mass distribution of galaxy clusters. Upcoming full-sky weak lensing surveys such as Euclid will offer for the first time the possibility to detect galaxy clusters based on their lensing signal i.e. directly on their total mass. This will allow us to build a galaxy cluster catalogue representative of the true cluster population, providing new constraints on galaxy cluster abundances in the Universe.
The goal of the project is to develop a new (unbiased) estimator of the mass of the clusters of galaxies selected by weak lensing.
While a simple deprojection of a standard spherical Navarro-Frenk-White (NFW) density model will give a first-order mass estimate, the triaxiality of the clusters introduces an important scatter in the mass estimate, as has been recently demonstrated by Giocoli et al. 2024. The use of the convergence helps mitigate this issue because it gives a direct access to the projected mass distribution (e.g. Pires et al 2020).

In a first part, the student will produce semi-analytical simulations of the expected weak Lensing signal from a cluster of galaxies based on the characteristics of the Euclid survey (noise, redshift distribution of the sources,…). Then, he will develop a new model-independent method to estimate the mass of the cluster from the convergence. The results will be compared to those obtained with traditional methods based on the shear signal.

The supervision of the thesis will be jointly performed by S. Pires (Astrostatistician and Weak Lensing expert) and Loris Chappuis (Cluster of galaxies expert). The student will be in a very stimulating context with the first quick release of Euclid Survey data currently planned for March 2025

Duration : 4 – 6 months

Location

Saclay

Internship conditions

• Internship duration: 4 months
• Level of study: Bac+5
• Training: Master 2
• Continuation in PhD thesis: No
• Application deadline: 28 février 2025

Useful methods and technics:
Astrophysics, Signal processing

Computer languages and software:
python 3

Supervisor

PIRES Sandrine
Phone: +33 1 69 08 80 72
Email :

Head of the laboratory DEDIP / LILAS

Andrea Formica
Phone: +33 1 69 08 82 34