Séminaire Univers /
Seminar Universe

 Weak gravitational lensing (WL) provides a direct and robust probe of the mass distribution of galaxy clusters without relying on assumptions about their dynamical state, making it particularly valuable for studying dynamically young clusters at high redshift. Accurate mass measurements of these systems are also essential for using the cluster mass function to constrain cosmological parameters and test the standard ?CDM cosmology. In this talk, I will present a comprehensive WL study of ~40 galaxy clusters at 0.8 < z < 2.0, building on a research program that I began during my PhD and have continued to develop. This work uses archival deep optical and near-infrared imaging obtained with the Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 Infrared Channel (WFC3/IR) aboard the Hubble Space Telescope (HST). The high resolution and sensitivity of HST allow us to detect faint background galaxies and measure their subtle lensing distortions, enabling robust mass measurements of these distant clusters.

I will first highlight WL analyses of several remarkable high-redshift clusters. SPT-CL J2106-5844 (z = 1.13) and ACT-CL J0102-4915 (“El Gordo”; z = 0.87) are exceptionally massive systems whose existence has previously been discussed as a potential challenge to ?CDM. Our WL measurements confirm that both clusters are indeed extremely massive and remain consistent with theoretical expectations within ?CDM. I will also present WL measurements of JKCS 041 (z = 1.80) and XLSSC 122 (z = 1.98), two galaxy clusters at cosmic noon with some of the highest-redshift WL detections to date.

Moving from individual clusters to the population as a whole, I will discuss how our WL measurements can be used to calibrate cluster mass–observable scaling relations at high redshift, providing a basis for estimating the masses of much larger samples of distant clusters discovered by current and future surveys. Together, these studies demonstrate the power of weak lensing to probe the mass properties of high-redshift galaxy clusters and to test structure formation in the ?CDM framework.