Euclid: A complete Einstein ring in NGC 6505

C. M. O’Riordan; L. J. Oldham; A. Nersesian; T. Li; T. E. Collett; D. Sluse; B. Altieri; B. Clément; K. G. C. Vasan; S. Rhoades; Y. Chen; T. Jones; C. Adami; R. Gavazzi; S. Vegetti; D. M. Powell; J. A. Acevedo Barroso; I. T. Andika; R. Bhatawdekar; A. R. Cooray; G. Despali; J. M. Diego; L. R. Ecker; A. Galan; P. Gómez-Alvarez; L. Leuzzi; M. Meneghetti; R. B. Metcalf; M. Schirmer; S. Serjeant; C. Tortora; M. Vaccari; G. Vernardos; M. Walmsley; A. Amara; S. Andreon; N. Auricchio; H. Aussel; C. Baccigalupi; M. Baldi; A. Balestra; S. Bardelli; A. Basset; P. Battaglia; R. Bender; D. Bonino; E. Branchini; M. Brescia; J. Brinchmann; A. Caillat; S. Camera; V. Capobianco; C. Carbone; J. Carretero; S. Casas; F. J. Castander; M. Castellano; G. Castignani; S. Cavuoti; A. Cimatti; C. Colodro-Conde; G. Congedo; C. J. Conselice; L. Conversi; Y. Copin; L. Corcione; F. Courbin; H. M. Courtois; M. Cropper; A. Da Silva; H. Degaudenzi; G. De Lucia; A. M. Di Giorgio; J. Dinis; F. Dubath; C. A. J. Duncan; X. Dupac; S. Dusini; M. Farina; S. Farrens; F. Faustini; S. Ferriol; N. Fourmanoit; M. Frailis; E. Franceschi; M. Fumana; S. Galeotta; W. Gillard; B. Gillis; C. Giocoli; B. R. Granett; A. Grazian; F. Grupp; L. Guzzo; S. V. H. Haugan; J. Hoar; H. Hoekstra; W. Holmes; I. Hook; F. Hormuth; A. Hornstrup; P. Hudelot; K. Jahnke; M. Jhabvala; B. Joachimi; E. Keihänen; S. Kermiche; A. Kiessling; M. Kilbinger; R. Kohley; B. Kubik; M. Kümmel; M. Kunz; H. Kurki-Suonio; O. Lahav; R. Laureijs; D. Le Mignant; S. Ligori; P. B. Lilje; V. Lindholm; I. Lloro; G. Mainetti; E. Maiorano; O. Mansutti; O. Marggraf; K. Markovic; M. Martinelli; N. Martinet; F. Marulli; R. Massey; E. Medinaceli; S. Mei; M. Melchior; Y. Mellier; E. Merlin; G. Meylan; M. Moresco; L. Moscardini; R. Nakajima; R. C. Nichol; S.-M. Niemi; J. W. Nightingale; C. Padilla; S. Paltani; F. Pasian; K. Pedersen; W. J. Percival; V. Pettorino; S. Pires; G. Polenta; M. Poncet; L. A. Popa; L. Pozzetti; F. Raison; R. Rebolo; A. Renzi; J. Rhodes; G. Riccio; H.-W. Rix; E. Romelli; M. Roncarelli; E. Rossetti; B. Rusholme; R. Saglia; Z. Sakr; A. G. Sánchez; D. Sapone; B. Sartoris; P. Schneider; T. Schrabback; A. Secroun; G. Seidel; S. Serrano; C. Sirignano; G. Sirri; L. Stanco; J. Steinwagner; P. Tallada-Crespí; I. Tereno; R. Toledo-Moreo; F. Torradeflot; I. Tutusaus; L. Valenziano; T. Vassallo; G. Verdoes Kleijn; A. Veropalumbo; Y. Wang; J. Weller; A. Zacchei; G. Zamorani; E. Zucca; C. Burigana; P. Casenove; A. Mora; V. Scottez; M. Viel; M. Jauzac; H. Dannerbauer

doi:10.1051/0004-6361/202453014

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Volume 694 (February 2025)

A&A, 694 (2025) A145

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Issue		A&A Volume 694, February 2025


Article Number		A145
Number of page(s)		13
Section		Extragalactic astronomy
DOI		https://doi.org/10.1051/0004-6361/202453014
Published online		10 February 2025

A&A, 694, A145 (2025)

Euclid: A complete Einstein ring in NGC 6505^⋆

C. M. O’Riordan¹^⋆⋆, L. J. Oldham², A. Nersesian³^,4, T. Li², T. E. Collett², D. Sluse³, B. Altieri⁵, B. Clément⁶^,7, K. G. C. Vasan⁸, S. Rhoades⁸, Y. Chen⁸, T. Jones⁸, C. Adami⁹, R. Gavazzi⁹^,10, S. Vegetti¹, D. M. Powell¹, J. A. Acevedo Barroso⁶, I. T. Andika¹¹^,1, R. Bhatawdekar⁵, A. R. Cooray¹², G. Despali¹³^,14^,15, J. M. Diego¹⁶, L. R. Ecker¹⁷^,18, A. Galan¹¹^,1, P. Gómez-Alvarez¹⁹^,5, L. Leuzzi¹³^,14, M. Meneghetti¹⁴^,15, R. B. Metcalf¹³^,14, M. Schirmer²⁰, S. Serjeant²¹, C. Tortora²², M. Vaccari²³^,24^,25, G. Vernardos²⁶^,27, M. Walmsley²⁸^,29, A. Amara³⁰, S. Andreon³¹, N. Auricchio¹⁴, H. Aussel³², C. Baccigalupi³³^,34^,35^,36, M. Baldi³⁷^,14^,15, A. Balestra³⁸, S. Bardelli¹⁴, A. Basset³⁹, P. Battaglia¹⁴, R. Bender¹⁸^,17, D. Bonino⁴⁰, E. Branchini⁴¹^,42^,31, M. Brescia⁴³^,22^,44, J. Brinchmann⁴⁵^,46, A. Caillat⁹, S. Camera⁴⁷^,48^,40, V. Capobianco⁴⁰, C. Carbone⁴⁹, J. Carretero⁵⁰^,51, S. Casas⁵²^,2, F. J. Castander⁵³^,54, M. Castellano⁵⁵, G. Castignani¹⁴, S. Cavuoti²²^,44, A. Cimatti⁵⁶, C. Colodro-Conde⁵⁷, G. Congedo⁵⁸, C. J. Conselice²⁹, L. Conversi⁵⁹^,5, Y. Copin⁶⁰, L. Corcione⁴⁰, F. Courbin⁶^,61^,62, H. M. Courtois⁶³, M. Cropper⁶⁴, A. Da Silva⁶⁵^,66, H. Degaudenzi⁶⁷, G. De Lucia³⁴, A. M. Di Giorgio⁶⁸, J. Dinis⁶⁵^,66, F. Dubath⁶⁷, C. A. J. Duncan²⁹, X. Dupac⁵, S. Dusini⁶⁹, M. Farina⁶⁸, S. Farrens³², F. Faustini⁷⁰^,55, S. Ferriol⁶⁰, N. Fourmanoit⁷¹, M. Frailis³⁴, E. Franceschi¹⁴, M. Fumana⁴⁹, S. Galeotta³⁴, W. Gillard⁷¹, B. Gillis⁵⁸, C. Giocoli¹⁴^,15, B. R. Granett³¹, A. Grazian³⁸, F. Grupp¹⁸^,17, L. Guzzo⁷²^,31, S. V. H. Haugan⁷³, J. Hoar⁵, H. Hoekstra⁷⁴, W. Holmes⁷⁵, I. Hook⁷⁶, F. Hormuth⁷⁷, A. Hornstrup⁷⁸^,79, P. Hudelot¹⁰, K. Jahnke²⁰, M. Jhabvala⁸⁰, B. Joachimi⁸¹, E. Keihänen⁸², S. Kermiche⁷¹, A. Kiessling⁷⁵, M. Kilbinger³², R. Kohley⁵, B. Kubik⁶⁰, M. Kümmel¹⁷, M. Kunz⁸³, H. Kurki-Suonio⁸⁴^,85, O. Lahav⁸¹, R. Laureijs⁸⁶^,87, D. Le Mignant⁹, S. Ligori⁴⁰, P. B. Lilje⁷³, V. Lindholm⁸⁴^,85, I. Lloro⁸⁸, G. Mainetti⁸⁹, E. Maiorano¹⁴, O. Mansutti³⁴, O. Marggraf⁹⁰, K. Markovic⁷⁵, M. Martinelli⁵⁵^,91, N. Martinet⁹, F. Marulli¹³^,14^,15, R. Massey⁹², E. Medinaceli¹⁴, S. Mei⁹³, M. Melchior⁹⁴, Y. Mellier⁹⁵^,10, E. Merlin⁵⁵, G. Meylan⁶, M. Moresco¹³^,14, L. Moscardini¹³^,14^,15, R. Nakajima⁹⁰, R. C. Nichol³⁰, S.-M. Niemi⁸⁶, J. W. Nightingale⁹⁶, C. Padilla⁹⁷, S. Paltani⁶⁷, F. Pasian³⁴, K. Pedersen⁹⁸, W. J. Percival⁹⁹^,100^,101, V. Pettorino⁸⁶, S. Pires³², G. Polenta⁷⁰, M. Poncet³⁹, L. A. Popa¹⁰², L. Pozzetti¹⁴, F. Raison¹⁸, R. Rebolo⁵⁷^,103^,104, A. Renzi¹⁰⁵^,69, J. Rhodes⁷⁵, G. Riccio²², H.-W. Rix²⁰, E. Romelli³⁴, M. Roncarelli¹⁴, E. Rossetti³⁷, B. Rusholme¹⁰⁶, R. Saglia¹⁷^,18, Z. Sakr¹⁰⁷^,108^,109, A. G. Sánchez¹⁸, D. Sapone¹¹⁰, B. Sartoris¹⁷^,34, P. Schneider⁹⁰, T. Schrabback¹¹¹, A. Secroun⁷¹, G. Seidel²⁰, S. Serrano⁵⁴^,112^,53, C. Sirignano¹⁰⁵^,69, G. Sirri¹⁵, L. Stanco⁶⁹, J. Steinwagner¹⁸, P. Tallada-Crespí⁵⁰^,51, I. Tereno⁶⁵^,113, R. Toledo-Moreo¹¹⁴, F. Torradeflot⁵¹^,50, I. Tutusaus¹⁰⁸, L. Valenziano¹⁴^,115, T. Vassallo¹⁷^,34, G. Verdoes Kleijn⁸⁷, A. Veropalumbo³¹^,42^,116, Y. Wang¹¹⁷, J. Weller¹⁷^,18, A. Zacchei³⁴^,33, G. Zamorani¹⁴, E. Zucca¹⁴, C. Burigana²⁵^,115, P. Casenove³⁹, A. Mora¹¹⁸, V. Scottez⁹⁵^,119, M. Viel³³^,34^,36^,35^,120, M. Jauzac¹²¹^,92^,122^,123 and H. Dannerbauer¹²⁴

¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
² Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX, UK
³ STAR Institute, Quartier Agora – Allée du six Août, 19c, B-4000 Liège, Belgium
⁴ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
⁵ ESAC/ESA, Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
⁶ Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
⁷ SCITAS, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
⁸ Department of Physics and Astronomy, University of California, Davis, CA 95616, USA
⁹ Aix-Marseille Université, CNRS, CNES, LAM, Marseille, France
¹⁰ Institut d’Astrophysique de Paris, UMR 7095, CNRS, and Sorbonne Université, 98 bis boulevard Arago, 75014 Paris, France
¹¹ Technical University of Munich, TUM School of Natural Sciences, Physics Department, James-Franck-Str. 1, 85748 Garching, Germany
¹² Department of Physics & Astronomy, University of California Irvine, Irvine, CA 92697, USA
¹³ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna, via Piero Gobetti 93/2, 40129 Bologna, Italy
¹⁴ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
¹⁵ INFN-Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
¹⁶ Instituto de Física de Cantabria, Edificio Juan Jordá, Avenida de los Castros, 39005 Santander, Spain
¹⁷ Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstrasse 1, 81679 München, Germany
¹⁸ Max Planck Institute for Extraterrestrial Physics, Giessenbachstr. 1, 85748 Garching, Germany
¹⁹ FRACTAL S.L.N.E., calle Tulipán 2, Portal 13 1A, 28231 Las Rozas de Madrid, Spain
²⁰ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²¹ School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
²² INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
²³ Inter-University Institute for Data Intensive Astronomy, Department of Astronomy, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa
²⁴ Inter-University Institute for Data Intensive Astronomy, Department of Physics and Astronomy, University of the Western Cape, 7535 Bellville, Cape Town, South Africa
²⁵ INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, 40129 Bologna, Italy
²⁶ Department of Physics and Astronomy, Lehman College of the CUNY, Bronx, NY 10468, USA
²⁷ American Museum of Natural History, Department of Astrophysics, New York, NY 10024, USA
²⁸ David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto, 50 St George Street, Toronto, Ontario M5S 3H4, Canada
²⁹ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
³⁰ School of Mathematics and Physics, University of Surrey, Guildford, Surrey GU2 7XH, UK
³¹ INAF-Osservatorio Astronomico di Brera, Via Brera 28, 20122 Milano, Italy
³² Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
³³ IFPU, Institute for Fundamental Physics of the Universe, via Beirut 2, 34151 Trieste, Italy
³⁴ INAF-Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34143 Trieste, Italy
³⁵ INFN, Sezione di Trieste, Via Valerio 2, 34127 Trieste, TS, Italy
³⁶ SISSA, International School for Advanced Studies, Via Bonomea 265, 34136 Trieste, TS, Italy
³⁷ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
³⁸ INAF-Osservatorio Astronomico di Padova, Via dell’Osservatorio 5, 35122 Padova, Italy
³⁹ Centre National d’Etudes Spatiales – Centre spatial de Toulouse, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France
⁴⁰ INAF-Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
⁴¹ Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
⁴² INFN-Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy
⁴³ Department of Physics “E. Pancini”, University Federico II, Via Cinthia 6, 80126 Napoli, Italy
⁴⁴ INFN section of Naples, Via Cinthia 6, 80126 Napoli, Italy
⁴⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto, Portugal
⁴⁶ Faculdade de Ciências da Universidade do Porto, Rua do Campo de Alegre, 4150-007 Porto, Portugal
⁴⁷ Dipartimento di Fisica, Università degli Studi di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁴⁸ INFN-Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁴⁹ INAF-IASF Milano, Via Alfonso Corti 12, 20133 Milano, Italy
⁵⁰ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Avenida Complutense 40, 28040 Madrid, Spain
⁵¹ Port d’Informació Científica, Campus UAB, C. Albareda s/n, 08193 Bellaterra (Barcelona), Spain
⁵² Institute for Theoretical Particle Physics and Cosmology (TTK), RWTH Aachen University, 52056 Aachen, Germany
⁵³ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
⁵⁴ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels, Barcelona, Spain
⁵⁵ INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
⁵⁶ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
⁵⁷ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38204 San Cristóbal de La Laguna, Tenerife, Spain
⁵⁸ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁵⁹ European Space Agency/ESRIN, Largo Galileo Galilei 1, 00044 Frascati, Roma, Italy
⁶⁰ Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822, Villeurbanne F-69100, France
⁶¹ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
⁶² Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig de Lluís Companys 23, 08010 Barcelona, Spain
⁶³ UCB Lyon 1, CNRS/IN2P3, IUF, IP2I Lyon, 4 rue Enrico Fermi, 69622 Villeurbanne, France
⁶⁴ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
⁶⁵ Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, Campo Grande, PT1749-016 Lisboa, Portugal
⁶⁶ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
⁶⁷ Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland
⁶⁸ INAF-Istituto di Astrofisica e Planetologia Spaziali, via del Fosso del Cavaliere, 100, 00100 Roma, Italy
⁶⁹ INFN-Padova, Via Marzolo 8, 35131 Padova, Italy
⁷⁰ Space Science Data Center, Italian Space Agency, via del Politecnico snc, 00133 Roma, Italy
⁷¹ Aix-Marseille Université, CNRS/IN2P3, CPPM, Marseille, France
⁷² Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
⁷³ Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, 0315 Oslo, Norway
⁷⁴ Leiden Observatory, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
⁷⁵ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁷⁶ Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
⁷⁷ Felix Hormuth Engineering, Goethestr. 17, 69181 Leimen, Germany
⁷⁸ Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
⁷⁹ Cosmic Dawn Center (DAWN), Copenhagen, Denmark
⁸⁰ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁸¹ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁸² Department of Physics and Helsinki Institute of Physics, Gustaf Hällströmin katu 2, 00014 University of Helsinki, Helsinki, Finland
⁸³ Université de Genève, Département de Physique Théorique and Centre for Astroparticle Physics, 24 quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
⁸⁴ Department of Physics, P.O. Box 64 00014 University of Helsinki, Helsinki, Finland
⁸⁵ Helsinki Institute of Physics, Gustaf Hällströmin katu 2, University of Helsinki, Helsinki, Finland
⁸⁶ European Space Agency/ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁸⁷ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
⁸⁸ NOVA optical infrared instrumentation group at ASTRON, Oude Hoogeveensedijk 4, 7991PD Dwingeloo, The Netherlands
⁸⁹ Centre de Calcul de l’IN2P3/CNRS, 21 avenue Pierre de Coubertin, 69627 Villeurbanne Cedex, France
⁹⁰ Universität Bonn, Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
⁹¹ INFN-Sezione di Roma, Piazzale Aldo Moro, 2 – c/o Dipartimento di Fisica, Edificio G. Marconi, 00185 Roma, Italy
⁹² Department of Physics, Institute for Computational Cosmology, Durham University, South Road DH1 3LE, UK
⁹³ Université Paris Cité, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
⁹⁴ University of Applied Sciences and Arts of Northwestern Switzerland, School of Engineering, 5210 Windisch, Switzerland
⁹⁵ Institut d’Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France
⁹⁶ School of Mathematics, Statistics and Physics, Newcastle University, Herschel Building, Newcastle-upon-Tyne NE1 7RU, UK
⁹⁷ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra (Barcelona), Spain
⁹⁸ DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 155, 2200 Copenhagen, Denmark
⁹⁹ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
¹⁰⁰ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
¹⁰¹ Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada
¹⁰² Institute of Space Science, Str. Atomistilor, nr. 409 Măgurele, Ilfov 077125, Romania
¹⁰³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁰⁴ Consejo Superior de Investigaciones Cientificas, Calle Serrano 117, 28006 Madrid, Spain
¹⁰⁵ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Via Marzolo 8, 35131 Padova, Italy
¹⁰⁶ Caltech/IPAC, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁰⁷ Institut für Theoretische Physik, University of Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany
¹⁰⁸ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, CNRS, UPS, CNES, 14 Av. Edouard Belin, 31400 Toulouse, France
¹⁰⁹ Université St Joseph, Faculty of Sciences, Beirut, Lebanon
¹¹⁰ Departamento de Física, FCFM, Universidad de Chile, Blanco Encalada 2008, Santiago, Chile
¹¹¹ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25/8, 6020 Innsbruck, Austria
¹¹² Satlantis, University Science Park, Sede Bld 48940, Leioa-Bilbao, Spain
¹¹³ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
¹¹⁴ Universidad Politécnica de Cartagena, Departamento de Electrónica y Tecnología de Computadoras, Plaza del Hospital 1, 30202 Cartagena, Spain
¹¹⁵ INFN-Bologna, Via Irnerio 46, 40126 Bologna, Italy
¹¹⁶ Dipartimento di Fisica, Università degli studi di Genova, and INFN-Sezione di Genova, via Dodecaneso 33, 16146 Genova, Italy
¹¹⁷ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
¹¹⁸ Aurora Technology for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
¹¹⁹ ICL, Junia, Université Catholique de Lille, LITL, 59000 Lille, France
¹²⁰ ICSC – Centro Nazionale di Ricerca in High Performance Computing, Big Data e Quantum Computing, Via Magnanelli 2, Bologna, Italy
¹²¹ Department of Physics, Centre for Extragalactic Astronomy, Durham University, South Road DH1 3LE, UK
¹²² Astrophysics Research Centre, University of KwaZulu-Natal, Westville Campus, Durban 4041, South Africa
¹²³ School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Westville Campus, Durban 4041, South Africa
¹²⁴ Instituto de Astrofísica de Canarias (IAC), Departamento de Astrofísica, Universidad de La Laguna (ULL), 38200 La Laguna, Tenerife, Spain

^⋆⋆ Corresponding author; conor@mpa-garching.mpg.de

Received: 15 November 2024
Accepted: 20 December 2024

Abstract

We report the discovery of a complete Einstein ring around the elliptical galaxy NGC 6505, at z = 0.042. This is the first strong gravitational lens discovered in Euclid and the first in an NGC object from any survey. The combination of the low redshift of the lens galaxy, the brightness of the source galaxy (I_E = 18.1 lensed, I_E = 21.3 unlensed), and the completeness of the ring make this an exceptionally rare strong lens, unidentified until its observation by Euclid. We present deep imaging data of the lens from the Euclid Visible Camera (VIS) and Near-Infrared Spectrometer and Photometer (NISP) instruments, as well as resolved spectroscopy from the Keck Cosmic Web Imager (KCWI). The Euclid imaging in particular presents one of the highest signal-to-noise ratio optical/near-infrared observations of a strong gravitational lens to date. From the KCWI data we measure a source redshift of z = 0.406. Using data from the Dark Energy Spectroscopic Instrument (DESI) we measure a velocity dispersion for the lens galaxy of σ_⋆ = 303 ± 15 km s⁻¹. We model the lens galaxy light in detail, revealing angular structure that varies inside the Einstein ring. After subtracting this light model from the VIS observation, we model the strongly lensed images, finding an Einstein radius of 2.″5, corresponding to 2.1 kpc at the redshift of the lens. This is small compared to the effective radius of the galaxy, R_eff ∼ 12.″3. Combining the strong lensing measurements with analysis of the spectroscopic data we estimate a dark matter fraction inside the Einstein radius of f_DM = (11.1_−3.5^+5.4)% and a stellar initial mass-function (IMF) mismatch parameter of α_IMF = 1.26_−0.08^+0.05, indicating a heavier-than-Chabrier IMF in the centre of the galaxy.

Key words: gravitational lensing: strong / surveys / galaxies: individual: NGC 6505

^⋆

This paper is published on behalf of the Euclid Consortium.

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Euclid: A complete Einstein ring in NGC 6505⋆

Euclid: A complete Einstein ring in NGC 6505^⋆