# 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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### Abstract

We present a multi-wavelength analysis of the core of the massive galaxy cluster MACS\,J0417.5-1154 ($z = 0.441$; MACS\;J0417). Our analysis takes advantage of VLT/MUSE observations which allow the spectroscopic confirmation of three strongly-lensed systems. One of these, nick-named \emph{The Doughnut}, consists of three complete 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 [OII] line emission. The best-fit mass model (rms of 0.38\arcsec) yields a two-dimensional enclosed mass of $M({\rm R <200\,kpc}) = (1.77\pm0.03)\times10^{14}\,\msun$ and almost perfect alignment between the peaks of the BCG light and the dark matter of ($0.5\pm0.5$)\arcsec . Our finding that a significant misalignment results when the radial image of \emph{The Doughnut} is omitted serves as an important caveat for studies of BCG-dark matter offsets in galaxy clusters. Using \emph{Chandra} data to map the intra-cluster gas, we observe an offset between the gas and dark-matter peaks of ($1.7\pm0.5$)\arcsec, and excellent alignment of the X-ray peak with the location of optical emission line associated with the BCG. We interpret all observational evidence in the framework of on-going merger activity, noting specifically that the coincidence between the gas peak and the peak of blue light from the BCG may be evidence of dense, cold gas leading to direct star formation. We use the surface area $\sigma_{\mu}$ above a given magnification factor $\mu$ as a metric to estimate the lensing power of MACS\,J0417. We obtain $\sigma(\mu > 3) = 0.22$\,arcmin$^2$ confirming MACS\,J0417 as an efficient gravitational lens. Finally, we discuss the differences between our mass model and Mahler et al. (2018).
Original language English 3082-3097 16 Monthly Notices of the Royal Astronomical Society 483 3 7 Dec 2018 https://doi.org/10.1093/mnras/sty3312 Published - 31 Mar 2019

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### Cite this

Jauzac, M., Mahler, G., Edge, A. C., Sharon, K., Gillman, S., Ebeling, H., ... Salome, P. (2019). The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE. Monthly Notices of the Royal Astronomical Society, 483(3), 3082-3097. https://doi.org/10.1093/mnras/sty3312

The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE. / Jauzac, Mathilde; Mahler, Guillaume; Edge, Alastair C.; Sharon, Keren; Gillman, Steven; Ebeling, Harald; Harvey, David; Richard, Johan; Hamer, Stephen L.; Fumagalli, Michele; Swinbank, A. Mark; Kneib, Jean-Paul; Massey, Richard; Salome, Philippe.

In: Monthly Notices of the Royal Astronomical Society, Vol. 483, No. 3, 31.03.2019, p. 3082-3097.

Research output: Contribution to journalArticle

Jauzac, M, Mahler, G, Edge, AC, Sharon, K, Gillman, S, Ebeling, H, Harvey, D, Richard, J, Hamer, SL, Fumagalli, M, Swinbank, AM, Kneib, J-P, Massey, R & Salome, P 2019, 'The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE', Monthly Notices of the Royal Astronomical Society, vol. 483, no. 3, pp. 3082-3097. https://doi.org/10.1093/mnras/sty3312
Jauzac, Mathilde ; Mahler, Guillaume ; Edge, Alastair C. ; Sharon, Keren ; Gillman, Steven ; Ebeling, Harald ; Harvey, David ; Richard, Johan ; Hamer, Stephen L. ; Fumagalli, Michele ; Swinbank, A. Mark ; Kneib, Jean-Paul ; Massey, Richard ; Salome, Philippe. / The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE. In: Monthly Notices of the Royal Astronomical Society. 2019 ; Vol. 483, No. 3. pp. 3082-3097.
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title = "The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE",
abstract = "We present a multi-wavelength analysis of the core of the massive galaxy cluster MACS\,J0417.5-1154 ($z = 0.441$; MACS\;J0417). Our analysis takes advantage of VLT/MUSE observations which allow the spectroscopic confirmation of three strongly-lensed systems. One of these, nick-named \emph{The Doughnut}, consists of three complete 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 [OII] line emission. The best-fit mass model (rms of 0.38\arcsec) yields a two-dimensional enclosed mass of $M({\rm R <200\,kpc}) = (1.77\pm0.03)\times10^{14}\,\msun$ and almost perfect alignment between the peaks of the BCG light and the dark matter of ($0.5\pm0.5$)\arcsec . Our finding that a significant misalignment results when the radial image of \emph{The Doughnut} is omitted serves as an important caveat for studies of BCG-dark matter offsets in galaxy clusters. Using \emph{Chandra} data to map the intra-cluster gas, we observe an offset between the gas and dark-matter peaks of ($1.7\pm0.5$)\arcsec, and excellent alignment of the X-ray peak with the location of optical emission line associated with the BCG. We interpret all observational evidence in the framework of on-going merger activity, noting specifically that the coincidence between the gas peak and the peak of blue light from the BCG may be evidence of dense, cold gas leading to direct star formation. We use the surface area $\sigma_{\mu}$ above a given magnification factor $\mu$ as a metric to estimate the lensing power of MACS\,J0417. We obtain $\sigma(\mu > 3) = 0.22$\,arcmin$^2$ confirming MACS\,J0417 as an efficient gravitational lens. Finally, we discuss the differences between our mass model and Mahler et al. (2018).",
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author = "Mathilde Jauzac and Guillaume Mahler and Edge, {Alastair C.} and Keren Sharon and Steven Gillman and Harald Ebeling and David Harvey and Johan Richard and Hamer, {Stephen L.} and Michele Fumagalli and Swinbank, {A. Mark} and Jean-Paul Kneib and Richard Massey and Philippe Salome",
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T1 - The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE

AU - Jauzac, Mathilde

AU - Mahler, Guillaume

AU - Edge, Alastair C.

AU - Sharon, Keren

AU - Gillman, Steven

AU - Ebeling, Harald

AU - Harvey, David

AU - Richard, Johan

AU - Hamer, Stephen L.

AU - Fumagalli, Michele

AU - Swinbank, A. Mark

AU - Kneib, Jean-Paul

AU - Massey, Richard

AU - Salome, Philippe

N1 - 15 pages, 6 figures, 8 tables, accepted for publication in MNRAS

PY - 2019/3/31

Y1 - 2019/3/31

N2 - We present a multi-wavelength analysis of the core of the massive galaxy cluster MACS\,J0417.5-1154 ($z = 0.441$; MACS\;J0417). Our analysis takes advantage of VLT/MUSE observations which allow the spectroscopic confirmation of three strongly-lensed systems. One of these, nick-named \emph{The Doughnut}, consists of three complete 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 [OII] line emission. The best-fit mass model (rms of 0.38\arcsec) yields a two-dimensional enclosed mass of $M({\rm R <200\,kpc}) = (1.77\pm0.03)\times10^{14}\,\msun$ and almost perfect alignment between the peaks of the BCG light and the dark matter of ($0.5\pm0.5$)\arcsec . Our finding that a significant misalignment results when the radial image of \emph{The Doughnut} is omitted serves as an important caveat for studies of BCG-dark matter offsets in galaxy clusters. Using \emph{Chandra} data to map the intra-cluster gas, we observe an offset between the gas and dark-matter peaks of ($1.7\pm0.5$)\arcsec, and excellent alignment of the X-ray peak with the location of optical emission line associated with the BCG. We interpret all observational evidence in the framework of on-going merger activity, noting specifically that the coincidence between the gas peak and the peak of blue light from the BCG may be evidence of dense, cold gas leading to direct star formation. We use the surface area $\sigma_{\mu}$ above a given magnification factor $\mu$ as a metric to estimate the lensing power of MACS\,J0417. We obtain $\sigma(\mu > 3) = 0.22$\,arcmin$^2$ confirming MACS\,J0417 as an efficient gravitational lens. Finally, we discuss the differences between our mass model and Mahler et al. (2018).

AB - We present a multi-wavelength analysis of the core of the massive galaxy cluster MACS\,J0417.5-1154 ($z = 0.441$; MACS\;J0417). Our analysis takes advantage of VLT/MUSE observations which allow the spectroscopic confirmation of three strongly-lensed systems. One of these, nick-named \emph{The Doughnut}, consists of three complete 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 [OII] line emission. The best-fit mass model (rms of 0.38\arcsec) yields a two-dimensional enclosed mass of $M({\rm R <200\,kpc}) = (1.77\pm0.03)\times10^{14}\,\msun$ and almost perfect alignment between the peaks of the BCG light and the dark matter of ($0.5\pm0.5$)\arcsec . Our finding that a significant misalignment results when the radial image of \emph{The Doughnut} is omitted serves as an important caveat for studies of BCG-dark matter offsets in galaxy clusters. Using \emph{Chandra} data to map the intra-cluster gas, we observe an offset between the gas and dark-matter peaks of ($1.7\pm0.5$)\arcsec, and excellent alignment of the X-ray peak with the location of optical emission line associated with the BCG. We interpret all observational evidence in the framework of on-going merger activity, noting specifically that the coincidence between the gas peak and the peak of blue light from the BCG may be evidence of dense, cold gas leading to direct star formation. We use the surface area $\sigma_{\mu}$ above a given magnification factor $\mu$ as a metric to estimate the lensing power of MACS\,J0417. We obtain $\sigma(\mu > 3) = 0.22$\,arcmin$^2$ confirming MACS\,J0417 as an efficient gravitational lens. Finally, we discuss the differences between our mass model and Mahler et al. (2018).

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