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Euclid : A complete Einstein ring in NGC 6505

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O’Riordan, C. M., Oldham, L. J., Nersesian, A., Li, T., Collett, T. E., Sluse, D., Altieri, B., Clément, B. +190 more·2025·Astronomy & Astrophysics
DOI 10.1051/0004-6361/202453014
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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.

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O’Riordan, C. M., Oldham, L. J., Nersesian, A., Li, T., Collett, T. E., Sluse, D., Altieri, B., Clément, B., Vasan, K. G. C., Rhoades, S., Chen, Y., Jones, T., Adami, C., Gavazzi, R., Vegetti, S., Powell, D. M., Acevedo Barroso, J. A., Andika, I. T., Bhatawdekar, R., Cooray, A. R., Despali, G., Diego, J. M., Ecker, L. R., Galan, A., Gómez-Alvarez, P., Leuzzi, L., Meneghetti, M., Metcalf, R. B., Schirmer, M., Serjeant, S., Tortora, C., Vaccari, M., Vernardos, G., Walmsley, M., Amara, A., Andreon, S., Auricchio, N., Aussel, H., Baccigalupi, C., Baldi, M., Balestra, A., Bardelli, S., Basset, A., Battaglia, P., Bender, R., Bonino, D., Branchini, E., Brescia, M., Brinchmann, J., Caillat, A., Camera, S., Capobianco, V., Carbone, C., Carretero, J., Casas, S., Castander, F. J., Castellano, M., Castignani, G., Cavuoti, S., Cimatti, A., Colodro-Conde, C., Congedo, G., Conselice, C. J., Conversi, L., Copin, Y., Corcione, L., Courbin, F., Courtois, H. M., Cropper, M., Da Silva, A., Degaudenzi, H., De Lucia, G., Di Giorgio, A. M., Dinis, J., Dubath, F., Duncan, C. A. J., Dupac, X., Dusini, S., Farina, M., Farrens, S., Faustini, F., Ferriol, S., Fourmanoit, N., Frailis, M., Franceschi, E., Fumana, M., Galeotta, S., Gillard, W., Gillis, B., Giocoli, C., Granett, B. R., Grazian, A., Grupp, F., Guzzo, L., Haugan, S. V. H., Hoar, J., Hoekstra, H., Holmes, W., Hook, I., Hormuth, F., Hornstrup, A., Hudelot, P., Jahnke, K., Jhabvala, M., Joachimi, B., Keihänen, E., Kermiche, S., Kiessling, A., Kilbinger, M., Kohley, R., Kubik, B., Kümmel, M., Kunz, M., Kurki-Suonio, H., Lahav, O., Laureijs, R., Le Mignant, D., Ligori, S., Lilje, P. B., Lindholm, V., Lloro, I., Mainetti, G., Maiorano, E., Mansutti, O., Marggraf, O., Markovic, K., Martinelli, M., Martinet, N., Marulli, F., Massey, R., Medinaceli, E., Mei, S., Melchior, M., Mellier, Y., Merlin, E., Meylan, G., Moresco, M., Moscardini, L., Nakajima, R., Nichol, R. C., Niemi, S.-M., Nightingale, J. W., Padilla, C., Paltani, S., Pasian, F., Pedersen, K., Percival, W. J., Pettorino, V., Pires, S., Polenta, G., Poncet, M., Popa, L. A., Pozzetti, L., Raison, F., Rebolo, R., Renzi, A., Rhodes, J., Riccio, G., Rix, H.-W., Romelli, E., Roncarelli, M., Rossetti, E., Rusholme, B., Saglia, R., Sakr, Z., Sánchez, A. G., Sapone, D., Sartoris, B., Schneider, P., Schrabback, T., Secroun, A., Seidel, G., Serrano, S., Sirignano, C., Sirri, G., Stanco, L., Steinwagner, J., Tallada-Crespí, P., Tereno, I., Toledo-Moreo, R., Torradeflot, F., Tutusaus, I., Valenziano, L., Vassallo, T., Verdoes Kleijn, G., Veropalumbo, A., Wang, Y., Weller, J., Zacchei, A., Zamorani, G., Zucca, E., Burigana, C., Casenove, P., Mora, A., Scottez, V., Viel, M., Jauzac, M., & Dannerbauer, H.
Affiliations
  • Max Planck Institute for Astrophysics (DE)
  • University of Portsmouth (GB)
  • University of Liège (BE)
  • European Space Astronomy Centre (ES)
  • École Polytechnique Fédérale de Lausanne (CH)
  • University of California, Davis (US)
  • Centre National de la Recherche Scientifique (FR)
  • University of California, Irvine (US)
  • Istituto Nazionale di Fisica Nucleare, Sezione di Bologna (IT)
  • Instituto de Física de Cantabria (ES)
  • Max Planck Institute for Extraterrestrial Physics (DE)
  • Osservatorio di Astrofisica e Scienza dello Spazio (IT)
  • Max Planck Institute for Astronomy (DE)
  • The Open University (GB)
  • Astronomical Observatory of Capodimonte (IT)
  • University of Cape Town (ZA)
  • American Museum of Natural History (US)
  • University of Toronto (CA)
  • University of Surrey (GB)
  • Brera Astronomical Observatory (IT)
  • Scuola Internazionale Superiore di Studi Avanzati (IT)
  • Osservatorio Astronomico di Padova (IT)
  • Centre National d'Études Spatiales (FR)
  • Osservatorio Astrofisico di Torino (IT)
  • Universidade do Porto (PT)
  • Istituto Nazionale di Fisica Nucleare, Sezione di Torino (IT)
  • National Institute for Astrophysics (IT)
  • Port d'Informació Científica (ES)
  • Institute of Space Sciences (ES)
  • Astronomical Observatory of Rome (IT)
  • University of Bologna (IT)
  • Instituto de Astrofísica de Canarias (ES)
  • Royal Observatory (GB)
  • University of Manchester (GB)
  • European Space Agency (FR)
  • Lyon 1 Université (FR)
  • Institució Catalana de Recerca i Estudis Avançats (ES)
  • University College London (GB)
  • University of Geneva (CH)
  • University of Lisbon (PT)
  • Istituto Nazionale di Fisica Nucleare, Sezione di Padova (IT)
  • Institute for Space Astrophysics and Planetology (IT)
  • Trieste Astronomical Observatory (IT)
  • University of Milan (IT)
  • University of Oslo (NO)
  • Leiden University (NL)
  • Jet Propulsion Laboratory (US)
  • Lancaster University (GB)
  • University of Copenhagen (DK)
  • Goddard Space Flight Center (US)
  • University of Helsinki (FI)
  • Ludwig-Maximilians-Universität München (DE)
  • University of Groningen (NL)
  • Netherlands Institute for Radio Astronomy (NL)
  • University of Bonn (DE)
  • Durham University (GB)
  • FHNW University of Applied Sciences and Arts Northwestern Switzerland (CH)
  • Newcastle University (GB)
  • University of Waterloo (CA)
  • Agenzia Spaziale Italiana (IT)
  • Institute of Space Science - INFLPR Subsidiary (RO)
  • Consejo Superior de Investigaciones Científicas (ES)
  • University of Padua (IT)
  • California Institute of Technology (US)
  • University of Chile (CL)
  • Universität Innsbruck (AT)
  • Universidad Politécnica de Cartagena (ES)
  • Istituto di Radioastronomia di Bologna (IT)
  • Université Catholique de Lille (FR)
  • Universidad de La Laguna (ES)
ORCID
Venue
Astronomy & Astrophysics
Publisher
EDP Sciences
Published
2025-02
Volume
694
Pages
A145
ISSN
  • 0004-6361 (ISSN-L)
  • 1432-0746
DOI
10.1051/0004-6361/202453014
OpenAlex
W4407342358
Cited by
17
References
84
Citations by year
2026: 7 · 2025: 10
FWCI
7.55
Type
journal article
Language
en
Open access
Licence
Locations
  • Astronomy and Astrophysics (publishedVersion, cc-by)
  • Research at the University of Copenhagen (University of Copenhagen) (publishedVersion, cc-by)
  • University of Groningen research database (University of Groningen / Centre for Information Technology) (publishedVersion, cc-by)
  • DIGITAL.CSIC (Spanish National Research Council (CSIC)) (acceptedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • Open Repository and Bibliography (University of Liège) (submittedVersion, other-oa)
  • Universidad de Chile (submittedVersion, cc-by-nc-nd)
  • Leiden Repository (Leiden University) (submittedVersion, cc-by)
  • HAL (submittedVersion, cc-by)
  • Archivio istituzionale della ricerca (Alma Mater Studiorum Università di Bologna) (submittedVersion, cc-by)
  • Lancaster EPrints (Lancaster University) (submittedVersion)
  • Työväentutkimus Vuosikirja (submittedVersion)
  • Infoscience (Ecole Polytechnique Fédérale de Lausanne) (submittedVersion, cc-by-nc-nd)
  • MPG.PuRe (Max Planck Society) (submittedVersion)
  • CINECA IRIS Institutial Research Information System (University of Genoa) (submittedVersion)
  • Padua Research Archive (University of Padova) (submittedVersion, cc-by)
  • arXiv (Cornell University)
Funders
  • National Science Foundation (DEAC02-05CH11231, 0950945)
  • U.S. Department of Energy (-AC02-05CH11231, 05CH11231, DE AC02 05CH11231, AST-0950945, DE-AC02-)
  • National Aeronautics and Space Administration (DE-AC02-05CH11231)
  • W. M. Keck Foundation (DE-AC02-05CH11231)
  • Gordon and Betty Moore Foundation
  • California Institute of Technology
  • European Space Agency
  • European Commission (HORIZON2020, DE-AC02-05CH11231, 945536)
  • Belgian Federal Science Policy Office (4000143347)
  • Consejo Nacional de Ciencia y Tecnología (DE-AC02-05CH11231)
  • Magyar Tudományos Akadémia
  • Agenzia Spaziale Italiana
  • Max-Planck-Gesellschaft (DE-AC02-05CH11231)
  • Centre National de la Recherche Scientifique (DE-AC02-05CH11231)
  • Ministerio de Ciencia e Innovación
  • National Astronomical Observatory of Japan
  • Commissariat à l'Énergie Atomique et aux Énergies Alternatives
  • Agenția Spațială Română
  • Norsk Romsenter
  • Office of Science (DEAC02–05CH11231, AC02-05CH11231, DE-AC02, 05CH11231)
  • Science and Technology Facilities Council (ST/Y001230/1, ST/X001229/1, ST/V000713/1)
  • Fundação para a Ciência e a Tecnologia (DE-AC02-05CH11231)
  • Division of Astronomical Sciences (DE-AC02-05CH11231, AST‐0950945)
  • Lawrence Berkeley National Laboratory (AC02‐05CH11231, DE-AC02-05CH11231, 05CH11231)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysical Phenomena and Observations
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
Keywords
Einstein ring, strong gravitational lensing, Euclid mission, dark matter fraction, initial mass function, Einstein radius, elliptical galaxies, source redshift

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