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RXJ0437+00: constraining dark matter with exotic gravitational lenses

Lagattuta, David J; Richard, Johan; Ebeling, Harald; Basto, Quentin; Cerny, Catherine; Edge, Alastair; Jauzac, Mathilde; Mahler, Guillaume; Massey, Richard

RXJ0437+00: constraining dark matter with exotic gravitational lenses Thumbnail


Johan Richard

Harald Ebeling

Quentin Basto


We present the first strong-gravitational-lensing analysis of the galaxy cluster RX J0437.1+0043 (RXJ0437; z = 0.285). Newly obtained, deep MUSE observations, Keck/MOSFIRE near-infrared spectroscopy, and Hubble Space Telescope SNAPshot imaging reveal 13 multiply imaged background galaxies, three of them (at z = 1.98, 2.97, and 6.02, respectively) in hyperbolic umbilic (H–U) lensing configurations. The H–U images are located only 20–50 kpc from the cluster centre, i.e. at distances well inside the Einstein radius where images from other lens configurations are demagnified and often unobservable. Extremely rare (only one H–U lens was known previously) these systems are able to constrain the inner slope of the mass distribution – and unlike radial arcs, the presence of H–U configurations is not biased towards shallow cores. The galaxies lensed by RXJ0437 are magnified by factors ranging from 30 to 300 and (in the case of H–U systems) stretched nearly isotropically. Taking advantage of this extreme magnification, we demonstrate how the source galaxies in H–U systems can be used to probe for small-scale (∼109 M⊙) substructures, providing additional insight into the nature of dark matter.


Lagattuta, D. J., Richard, J., Ebeling, H., Basto, Q., Cerny, C., Edge, A., …Massey, R. (2023). RXJ0437+00: constraining dark matter with exotic gravitational lenses. Monthly Notices of the Royal Astronomical Society, 522(1), 1091-1107.

Journal Article Type Article
Acceptance Date Mar 10, 2023
Online Publication Date Apr 18, 2023
Publication Date 2023
Deposit Date May 16, 2023
Publicly Available Date May 16, 2023
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 522
Issue 1
Pages 1091-1107


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Copyright Statement
© The Author(s) 2023.
Published by Oxford University Press on behalf of 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.

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