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The extraordinary amount of substructure in the Hubble Frontier Fields Cluster Abell 2744.

Jauzac, M. and Eckert, D. and Schwinn, J. and Harvey, D. and Baugh, C. M. and Robertson, A. and Bose, S. and Massey, R. and Owers, M. and Ebeling, H. and Shan, H. Y. and Jullo, E. and Kneib, J.-P. and Richard, J. and Atek, H. and Clément, B. and Egami, E. and Israel, H. and Knowles, K. and Limousin, M. and Natarajan, P. and Rexroth, M. and Taylor, P. and Tchernin, C. (2016) 'The extraordinary amount of substructure in the Hubble Frontier Fields Cluster Abell 2744.', Monthly notices of the Royal Astronomical Society., 463 (4). pp. 3876-3893.


We present a joint optical/X-ray analysis of the massive galaxy cluster Abell 2744 (z=0.308). Our strong- and weak-lensing analysis within the central region of the cluster, i.e., at R < 1 Mpc from the brightest cluster galaxy, reveals eight substructures, including the main core. All of these dark-matter halos are detected with a significance of at least 5σ and feature masses ranging from 0.5 to 1.4× 1014M⊙ within R < 150 kpc. Merten et al. (2011) and Medezinski et al. (2016) substructures are also detected by us. We measure a slightly higher mass for the main core component than reported previously and attribute the discrepancy to the inclusion of our tightly constrained strong-lensing mass model built on Hubble Frontier Fields data. X-ray data obtained by XMM-Newton reveal four remnant cores, one of them a new detection, and three shocks. Unlike Merten et al. (2011), we find all cores to have both dark and luminous counterparts. A comparison with clusters of similar mass in the MXXL simulations yields no objects with as many massive substructures as observed in Abell 2744, confirming that Abell 2744 is an extreme system. We stress that these properties still do not constitute a challenge to ΛCDM, as caveats apply to both the simulation and the observations: for instance, the projected mass measurements from gravitational lensing and the limited resolution of the sub-haloes finders. We discuss implications of Abell 2744 for the plausibility of different dark-matter candidates and, finally, measure a new upper limit on the self-interaction cross-section of dark matter of σDM < 1.28 cm2g−1(68% CL), in good agreement with previous results from Harvey et al. (2015).

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:05 September 2016
Date deposited:06 October 2016
Date of first online publication:07 September 2016
Date first made open access:No date available

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