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Reconciling galaxy cluster shapes, measured by theorists versus observers

Harvey, David and Robertson, Andrew and Tam, Sut-Ieng and Jauzac, Mathilde and Massey, Richard and Rhodes, Jason and McCarthy, Ian G. (2021) Reconciling galaxy cluster shapes, measured by theorists versus observers. Monthly Notices of the Royal Astronomical Society, 500 (2). pp. 2627-2644. ISSN 0035-8711.

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If properly calibrated, the shapes of galaxy clusters can be used to investigate many physical processes: from feedback and quenching of star formation, to the nature of dark matter. Theorists frequently measure shapes using moments of inertia of simulated particles’. We instead create mock (optical, X-ray, strong-, and weak-lensing) observations of the 22 most massive (⁠∼10^(14.7) M_⊙⁠) relaxed clusters in the BAHAMAS simulations. We find that observable measures of shape are rounder. Even when moments of inertia are projected into 2D and evaluated at matched radius, they overestimate ellipticity by 56 per cent (compared to observable strong lensing) and 430 per cent (compared to observable weak lensing). Therefore, we propose matchable quantities and test them using observations of eight relaxed clusters from the Hubble Space Telescope (HST) and Chandra X-Ray Observatory. We also release our HST data reduction and lensing analysis software to the community. In real clusters, the ellipticity and orientation angle at all radii are strongly correlated. In simulated clusters, the ellipticity of inner (<r_(vir)/20) regions becomes decoupled: for example, with greater misalignment of the central cluster galaxy. This may indicate overly efficient implementation of feedback from active galactic nuclei. Future exploitation of cluster shapes as a function of radii will require better understanding of core baryonic processes. Exploitation of shapes on any scale will require calibration on simulations extended all the way to mock observations.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Harvey, David0000-0002-6066-6707
Robertson, Andrew0000-0002-0086-0524
Tam, Sut-Ieng0000-0002-6724-833X
Jauzac, Mathilde0000-0003-1974-8732
Massey, Richard0000-0002-6085-3780
Rhodes, Jason0000-0002-4485-8549
McCarthy, Ian G.0000-0002-1286-483X
Alternate Title:Reconciling galaxy cluster shapes, measured by theorists vs observers
Additional Information:© The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Accepted 2020 October 6. Received 2020 August 31; in original form 2020 July 17. DH acknowledges support by the Delta Institute for Theoretical Physics. JR was supported by JPL, which is run under a contract for NASA by Caltech. MJ is supported by the United Kingdom Research and Innovation (UKRI) Future Leaders Fellowship ‘Using Cosmic Beasts to uncover the Nature of Dark Matter’ [grant number MR/S017216/1]. This project was also supported by the Science and Technology Facilities Council [grant number ST/L00075X/1]. SIT is supported by Van Mildert College Trust PhD Scholarships. RM is supported by the Royal Society. AR is supported by the European Research Council’s Horizon 2020 project ‘EWC’ (award AMD- 776247-6). 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 769130). DATA AVAILABILITY. Although data are private, it is available upon request.
Funding AgencyGrant Number
Delta Institute for Theoretical PhysicsUNSPECIFIED
United Kingdom Research and Innovation (UKRI)MR/S017216/1
Science and Technology Facilities Council (STFC)ST/L00075X/1
Van Mildert College TrustUNSPECIFIED
Euorpean Research Council (ERC)AMD-776247-6
European Research Council (ERC)769130
Subject Keywords:gravitational lensing: strong, gravitational lensing: weak, galaxies: clusters: general, dark matter, X-rays: galaxies: cluster
Issue or Number:2
Record Number:CaltechAUTHORS:20210205-145941012
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Official Citation:David Harvey, Andrew Robertson, Sut-Ieng Tam, Mathilde Jauzac, Richard Massey, Jason Rhodes, Ian G McCarthy, Reconciling galaxy cluster shapes, measured by theorists versus observers, Monthly Notices of the Royal Astronomical Society, Volume 500, Issue 2, January 2021, Pages 2627–2644,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107940
Deposited By: George Porter
Deposited On:05 Feb 2021 23:26
Last Modified:05 Feb 2021 23:26

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