The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE

Mathilde Jauzac, Guillaume Mahler, Alastair C. Edge, Keren Sharon, Steven Gillman, Harald Ebeling, David Harvey, Johan Richard, Stephen L. Hamer, Michele Fumagalli, A. Mark Swinbank, Jean-Paul Kneib, Richard Massey, Philippe Salome

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We present a multiwavelength analysis of the core of the massive galaxy cluster MACS J0417.5.1154 (z = 0.441). Our analysis takes advantage of Very Large Telescope/Multi-Unit Spectroscopic Explorer observations which allowthe spectroscopic confirmation of three strongly lensed systems. System #1, nicknamed The Doughnut, consists of three images of a complex ring galaxy at z = 0.8718 and a fourth, partial and radial image close to the brightest cluster galaxy (BCG) only discernible thanks to its strong [O II] line emission. The best-fitting mass model (rms of 0.38 arcsec) yields a two-dimensional enclosed mass of M(R < 200 kpc) = (1.77 ± 0.03) × 10 14M and almost perfect alignment between the peaks of the BCG light and the dark matter of (0.5 ± 0.5) arcsec. We observe a significant misalignment when system #1 radial image is omitted. The result serves as an important caveat for studies of BCG-dark-matter offsets in galaxy clusters. Using Chandra to map the intracluster gas, we observe an offset between gas and dark matter of (1.7 ± 0.5) arcsec, and excellent alignment of the X-ray peak with the location of optical emission line associated with the BCG. We interpret all observational evidences in the framework of ongoing cluster merger activity, noting specifically that the coincidence between the gas and optical line peaks may be evidence of dense, cold gas cooled directly from the intracluster gas. Finally, we measure the surface area, σ μ, above a given magnification factor μ, a metric to estimate the lensing power of a lens, σ(μ > 3) = 0.22 arcmin 2, which confirms MACS J0417 as an efficient gravitational lens.

Original languageEnglish
Pages (from-to)3082-3097
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date7 Dec 2018
Publication statusPublished - 31 Mar 2019

Bibliographical note

Funding Information:
The authors thank the anonymous referee for their useful comments. MJ thanks D. Eckert for useful discussions. We thank the RELICS team for releasing the fully reduced HST imaging data, available to the community as hlsp through MAST. We thank Joshua Stephenson for his hard work creating the MUSE observation files. This work was supported by the Science and Technology Facilities Council (grant numbers ST/L00075X/1 and ST/P00541/1) and used the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility ( This equipment was funded by BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/H008519/1, and STFC DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the National E-Infrastructure. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 757535). This paper is based on observations made with the NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-14096. Archival data are associated with program GO-12009.

Publisher Copyright:
© 2018 The Author(s).


  • Dark matter
  • Galaxies: clusters: individual: MACS J0417.5-1154
  • Gravitational lensing: strong

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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