Abstract

Contributed Talk - Splinter GalaxyClusters

Wednesday, 09 September 2026, 14:15   (MW-1050)

Weak Lensing Analysis of High-z Galaxy Clusters

Zimmermann, N.
Universität Innsbruck

Massive clusters trace the densest regions in the cosmic large-scale structure. Their growth is completely dominated by gravity, which is why robust constraints on their number density as a function of mass and redshift offer a powerful approach to probe the cosmological model using well-understood physics. Very massive clusters are expected to be rare, especially at high redshifts (z >∼ 0.7). With only modest samples the study of these extreme objects can provide unique constraints on models beyond ΛCDM, such as early dark energy scenarios, which might help to resolve the Hubble tension. To enable the comparison to cosmological predictions we require both a well-understood sample selection and an accurate calibration of cluster mass estimates using weak lensing. We present VLT weak gravitational lensing study of 31 distant and massive galaxy clusters with redshifts ranging from 0.7 to 1.3, with a median redshift of z~0.8. Five of them are X-ray detected and first listed in the first all sky survey of the eROSITA mission, 26 have been detected via the Sunyaev Zel'dovich (SZ) effect and are listed in the South Pole Telescope SZ sample (SPT-SZ, 16) and the SPT Extended Cluster Survey sample (ECS, 9). We measured weak lensing galaxy shapes in VLT/HAWK-I Ks-band images and used complementary VLT/FORS2 g- and z-band images for a stringent and efficient background selection in g-z and z-Ks colour-colour space. We obtained a mean full width at half maximum of the point spread function of 0''.3-0''.4 in the VLT/HAWK-I Ks-band and for the target with the deepest Ks-band data a background source density of 25 background galaxies per square arcmin. We expect our measured shear signals to be a valuable contribution to an accurate calibration of high-z cluster masses using weak lensing.