Sut-Ieng Tam

Using the largest mosaic of Hubble Space Telescope images around a galaxy cluster, we map the distribution of dark matter throughout a ∼6×6 Mpc^2 area centred on the cluster MS 0451-03 (z=0.54). We preform a joint strong- and weak-lensing analysis using Lenstool software. The strong lensing constraints are based on the best-fit strong-lensing mass model from Jauzac et al. 2020. For the weak-lensing regime, we calibrated the weak-lensing shear signal using pyRRG and selected the background sources based on their photometric redshift and color. The combined strong and weak-lensing analysis provided a wide-field lensing 2D mass map of this cluster. Its main dark matter halo is clearly detected, with elongation along North-West to South-East direction. We constrained the fundamental properties of MS 0451-03, e.g. M200c= (1.65 ± 0.24) × 10^15M⊙, c200c=3.79 ± 0.36, axis-ratio=q = 0.48 ± 0.01 and Baryonic-mass fraction, fb,500 = (14.6±1.4)%. In the surrounding environment, thanks to the high resolution space-based imaging data, we detected a total of six cluster substructures with total lensing mass: 
6.1< M(10^13M⊙) <13.5 within a circular aperture of R < 480kpc. Based on the alignment of these group-scale substructures, we show three possible filaments extending from the cluster.

From our lensing analysis, the dark-matter distribution in the cluster core is elongated, consists of two distinct components, and is characterized by a concentration parameter of c200=3.79±0.36. By contrast, XMM-Newton observations show the gas distribution to be more spherical, with excess entropy near the core, and a lower concentration of c200=2.35±0.89 (assuming hydrostatic equilibrium). Such a configuration is predicted in simulations of major mergers 2-7 Gyr after the first core passage, when the two dark-matter halos approach second turnaround, and before their gas relaxed.
This inferred dynamical history provides a possible explanation for the quenched star formation history observed in this system by Moran et al. 2007. This quenched star formation can be explained by the increased ram pressure stripping due to the major merger about 5 Gyr ago.

Therefore, MS 0451-03 will be an ideal target for future studies of the growth of structure along filaments, star-formation processes after a major merger, and the late-stage evolution of cluster collisions.