The distribution of dark matter and gas spanning 6 Mpc around the post-merger galaxy cluster MS 0451-03
Smith, Graham P.; Ellis, Richard S.; Massey, Richard; Kneib, Jean-Paul; Jauzac, Mathilde; Harvey, David; Robertson, Andrew; Natarajan, Priyamvada; Ebeling, Harald; Tam, Sut-Ieng; Klein, Baptiste; Lagattuta, David; Eckert, Dominique; Ghirardini, Vittorio
United Kingdom, South Africa, Netherlands, Germany, Switzerland, United States, France
Abstract
Using the largest mosaic of Hubble Space Telescope images around a galaxy cluster, we map the distribution of dark matter throughout an ∼6 × 6 Mpc2 area centred on the cluster MS 0451-03 (z = 0.54, $M_{200}=1.65\times 10^{15}\, {\rm M}_{\odot }$ ). Our joint strong- and weak-lensing analysis shows three possible filaments extending from the cluster, encompassing six group-scale substructures. 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 $c_{200}=2.35^{+0.89}_{-0.70}$ (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 haloes approach second turnaround, and before their gas has relaxed. This post-merger scenario finds further support in optical spectroscopy of the cluster's member galaxies, which shows that star formation was abruptly quenched 5 Gyr ago. 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.