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Precision Modeling of JWST's First Cluster Lens SMACS J0723.3–7327*

Mahler, Guillaume; Jauzac, Mathilde; Richard, Johan; Beauchesne, Benjamin; Ebeling, Harald; Lagattuta, David; Natarajan, Priyamvada; Sharon, Keren; Atek, Hakim; Claeyssens, Adélaïde; Clément, Benjamin; Eckert, Dominique; Edge, Alastair; Kneib, Jean-Paul; Niemiec, Anna

Precision Modeling of JWST's First Cluster Lens SMACS J0723.3–7327* Thumbnail


Johan Richard

Benjamin Beauchesne

Harald Ebeling

Priyamvada Natarajan

Keren Sharon

Hakim Atek

Adélaïde Claeyssens

Benjamin Clément

Dominique Eckert

Alastair Edge

Jean-Paul Kneib

Anna Niemiec


Exploiting the fundamentally achromatic nature of gravitational lensing, we present a lens model for the massive galaxy cluster SMACS J0723.3−7323 (SMACS J0723; z = 0.388) that significantly improves upon earlier work. Building on strong-lensing constraints identified in prior Hubble Space Telescope (HST) observations, the mass model utilizes 21 multiple-image systems, 17 of which were newly discovered in Early Release Observation data from the JWST. The resulting lens model maps the cluster mass distribution to an rms spatial precision of 0farcs32, and is publicly available. Consistent with previous analyses, our study shows SMACS J0723.3 to be well described by a single large-scale component centered on the location of the brightest cluster galaxy. However, satisfying all lensing constraints provided by the JWST data, the model points to the need for the inclusion of an additional, diffuse component west of the cluster. A comparison of the galaxy, mass, and gas distributions in the core of SMACS J0723 based on HST, JWST, and Chandra data reveals a concentrated regular elliptical profile along with tell-tale signs of a recent merger, possibly proceeding almost along our line of sight. The exquisite sensitivity of JWST's NIRCam reveals in spectacular fashion both the extended intracluster light distribution and numerous star-forming clumps in magnified background galaxies. The high-precision lens model derived here for SMACS J0723 demonstrates the unprecedented power of combining HST and JWST data for studies of structure formation and evolution in the distant universe.


Mahler, G., Jauzac, M., Richard, J., Beauchesne, B., Ebeling, H., Lagattuta, D., …Niemiec, A. (2023). Precision Modeling of JWST's First Cluster Lens SMACS J0723.3–7327*. Astrophysical Journal, 945(1), Article 49.

Journal Article Type Article
Acceptance Date Dec 20, 2022
Online Publication Date Mar 7, 2023
Publication Date Mar 1, 2023
Deposit Date Jun 20, 2023
Publicly Available Date Jun 20, 2023
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 945
Issue 1
Article Number 49


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Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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