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Growing a ‘cosmic beast’: observations and simulations of MACS J0717.5+3745

Jauzac, M.; Eckert, D.; Schaller, M.; Schwinn, J.; Massey, R.; Bahé, Y.; Baugh, C.; Barnes, D.; Dalla Vecchia, C.; Ebeling, H.; Harvey, D.; Jullo, E.; Kay, S.T.; Kneib, J.-P.; Limousin, M.; Medezinski, E.; Natarajan, P.; Nonino, M.; Robertson, A.; Tam, S.I.; Umetsu, K.

Growing a ‘cosmic beast’: observations and simulations of MACS J0717.5+3745 Thumbnail


D. Eckert

M. Schaller

J. Schwinn

Y. Bahé

D. Barnes

C. Dalla Vecchia

H. Ebeling

D. Harvey

E. Jullo

S.T. Kay

J.-P. Kneib

M. Limousin

E. Medezinski

P. Natarajan

M. Nonino

A. Robertson

S.I. Tam

K. Umetsu


We present a gravitational lensing and X-ray analysis of a massive galaxy cluster and its surroundings. The core of MACS J0717.5+3745 (M(R < 1 Mpc) ∼ 2 × 1015 M, z = 0.54) is already known to contain four merging components. We show that this is surrounded by at least seven additional substructures with masses ranging 3.8−6.5 × 1013 M, at projected radii 1.6–4.9 Mpc. We compare MACS J0717 to mock lensing and X-ray observations of similarly rich clusters in cosmological simulations. The low gas fraction of substructures predicted by simulations turns out to match our observed values of 1–4 per cent. Comparing our data to three similar simulated haloes, we infer a typical growth rate and substructure infall velocity. That suggests MACS J0717 could evolve into a system similar to, but more massive than, Abell 2744 by z = 0.31, and into a ∼ 1016 M supercluster by z = 0. The radial distribution of infalling substructure suggests that merger events are strongly episodic; however, we find that the smooth accretion of surrounding material remains the main source of mass growth even for such massive clusters.


Jauzac, M., Eckert, D., Schaller, M., Schwinn, J., Massey, R., Bahé, Y., …Umetsu, K. (2018). Growing a ‘cosmic beast’: observations and simulations of MACS J0717.5+3745. Monthly Notices of the Royal Astronomical Society, 481(3), 2901-2917.

Journal Article Type Article
Acceptance Date Aug 21, 2018
Online Publication Date Aug 31, 2018
Publication Date Dec 11, 2018
Deposit Date Sep 24, 2018
Publicly Available Date Sep 25, 2018
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 481
Issue 3
Pages 2901-2917
Related Public URLs


Published Journal Article (2.5 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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