STRONG LENSING AND STELLAR KINEMATICS OF CLUSTER GALAXIES

This Thesis focuses on the study of the physical properties of the cluster galaxies with strong lensing and stellar kinematics. Our work aims at improving strong lensing modelling of galaxy clusters through a more accurate description of the member galaxies, and at testing the discrepancy between the observed compactness of the cluster galaxies and the predictions of cosmological hydrodynamical simulations. We used the observed kinematics of early-type cluster galaxies, from deep VLT/MUSE integral-field spectroscopy, to enhance the description of the cluster members in strong lensing models of massive galaxy clusters. We present a new strong lensing model of the cluster Abell S1063, improved by calibrating the Fundamental Plane relation for the cluster members and using it to obtain more accurate information on their total mass distribution. With this novel technique, we could measure the velocity dispersion of the members with more realistic and complex scaling laws than previous works, constraining the structure and mass function of the cluster sub-haloes with unprecedented accuracy. As a following step, we built galaxy-scale lensing models of cluster members to probe their truncation. This work significantly extends the study of early-type galaxies to fainter masses and lower magnitudes, finding that the tidal truncation they undergo does not significantly affect their inner structure. Our work has been used to compare the predictions of lensing models and cosmological hydrodynamical simulations, confirming the extremely compact structure of cluster galaxies, which is not reproduced by simulations. This results possibly points to potential shortcomings in our baryon feedback modelling, or even in the ΛCDM framework. Finally, we present our work in progress on constraining the line-of-sight velocity distribution for a larger sample of galaxies in strong lensing clusters, to calibrate their velocity function and gain further insights on their structure and on the evolutionary processes that shape them.