JWST’s PEARLS: A new lens model for ACT-CL J0102−4915, “El Gordo,” and the first red supergiant star at cosmological distances discovered by JWST

¹ Instituto de Física de Cantabria (CSIC-UC), Avda. Los Castros s/n, 39005 Santander, Spain
e-mail: jdiego@ifca.unican.es
² Physics Department, Ben-Gurion University of the Negev, PO Box 653, Beer-Sheva 8410501, Israel
³ Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁴ Department of Theoretical Physics, University of the Basque Country UPV-EHU, 48040 Bilbao, Spain
⁵ Donostia International Physics Center (DIPC), Manuel Lardizabal Ibilbidea 4, 20018 Donostia, Gipuzkoa, Spain
⁶ IKERBASQUE, Basque Foundation for Science, Alameda Urquijo, 36-5, 48008 Bilbao, Spain
⁷ Department of Physics, 366 Physics North MC 7300, University of California, Berkeley, CA 94720, USA
⁸ AURA for the European Space Agency (ESA), Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21210, USA
⁹ Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, AZ 85721-0009, USA
¹⁰ School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA
¹¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21210, USA
¹² Department of Astronomy, University of California, 501 Campbell Hall #3411, Berkeley, CA 94720, USA
¹³ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
¹⁴ Observational Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
¹⁵ School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA
¹⁶ International Centre for Radio Astronomy Research (ICRAR) and the International Space Centre (ISC), The University of Western Australia, M468, 35 Stirling Highway, Crawley, WA 6009, Australia
¹⁷ Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
¹⁸ National Research Council of Canada, Herzberg Astronomy & Astrophysics Research Centre, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹⁹ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Stromlo, Australia
²⁰ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
²¹ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
²² Cosmic Dawn Center (DAWN), Rådmandsgade 62, 2200 Copenhagen, Denmark

Received: 17 October 2022
Accepted: 16 January 2023

Abstract

The first James Webb Space Telescope (JWST) data on the massive colliding cluster El Gordo allow for 23 known families of multiply lensed images to be confirmed and for eight new members of these families to be identified. Based on these families, which have been confirmed spectroscopically by MUSE, we derived an initial lens model. This model guided the identification of 37 additional families of multiply lensed galaxies, among which 28 are entirely new systems, and nine were previously known. The initial lens model determined geometric redshifts for the 37 new systems. The geometric redshifts agree reasonably well with spectroscopic or photometric redshifts when those are available. The geometric redshifts enable two additional models that include all 60 families of multiply lensed galaxies spanning a redshift range 2 < z < 6. The derived dark-matter distribution confirms the double-peak configuration of mass found by earlier work with the southern and northern clumps having similar masses. We confirm that El Gordo is the most massive known cluster at z > 0.8 and has an estimated virial mass close the maximum mass allowed by standard cosmological models. The JWST images also reveal the presence of small-mass perturbers that produce small lensing distortions. The smallest of these is consistent with being a dwarf galaxy at z = 0.87 and has an estimated mass of 3.8 × 10⁹ M_⊙, making it the smallest substructure found at z > 0.5. The JWST images also show several candidate caustic-crossing events. One of them is detected at high significance at the expected position of the critical curve and is likely a red supergiant star at z = 2.1878. This would be the first red supergiant found at cosmological distances. The cluster lensing should magnify background objects at z > 6, making more of them visible than in blank fields of a similar size, but there appears to be a deficiency of such objects.