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Department of Physics

# Staff profile

## Publication details for Prof Richard Massey

Medezinski E., Umetsu K., Okabe N., Nonino M., Molnar S., Massey R., Dupke R. & Merten J. (2016). Frontier Fields: Subaru Weak-Lensing Analysis of the Merging Galaxy Cluster A2744. Astrophysical Journal 817(1): 24.

### Abstract

We present a weak-lensing analysis of the merging Frontier Fields (FF) cluster Abell 2744 using new Subaru/Suprime-Cam imaging. The wide-field lensing mass distribution reveals this cluster is comprised of four distinct substructures. Simultaneously modeling the two-dimensional reduced shear field using a combination of a Navarro–Frenk–White (NFW) model for the main core and truncated NFW models for the subhalos, we determine their masses and locations. The total mass of the system is constrained as ${M}_{200{\rm{c}}}=(2.06\pm 0.42)\times {10}^{15}\;{M}_{\odot }.$ The most massive clump is the southern component with ${M}_{200{\rm{c}}}=(7.7\pm 3.4)\times {10}^{14}\;{M}_{\odot },$ followed by the western substructure (${M}_{200{\rm{c}}}=(4.5\pm 2.0)\times {10}^{14}\;{M}_{\odot }$) and two smaller substructures to the northeast (${M}_{200{\rm{c}}}=(2.8\pm 1.6)\times {10}^{14}\;{M}_{\odot }$) and northwest (${M}_{200{\rm{c}}}=(1.9\pm 1.2)\times {10}^{14}\;{M}_{\odot }$). The presence of the four substructures supports the picture of multiple mergers. Using a composite of hydrodynamical binary simulations we explain this complicated system without the need for a "slingshot" effect to produce the northwest X-ray interloper, as previously proposed. The locations of the substructures appear to be offset from both the gas (${87}_{-28}^{+34}$ arcsec, 90% CL) and the galaxies (${72}_{-53}^{+34}$ arcsec, 90% CL) in the case of the northwestern and western subhalos. To confirm or refute these findings, high resolution space-based observations extending beyond the current FF limited coverage to the west and northwestern area are essential.