Euclid Quick Data Release (Q1)

Astronomy and Astrophysics, vol. 711, pp. A32

Abstract

In the era of large-scale surveys such as Euclid , machine learning has become an essential tool for identifying rare yet scientifically valuable objects, such as strong gravitational lenses. However, supervised machine-learning approaches require large quantities of labelled examples to train on, and the limited number of known strong lenses has led to a reliance on simulations for training. A well-known challenge is that machine-learning models trained on one data domain often underperform when applied to a different domain: in the context of lens finding, this means that strong performance on simulated lenses does not necessarily translate into equally good performance on real observations. In the Euclid Quick Data Release 1 (Q1), covering 63 deg 2 , 500 strong lens candidates were discovered through a synergy of machine learning, citizen science, and expert visual inspection. These discoveries now allow us to quantify this performance gap and investigate the impact of training on real data. We find that a network trained only on simulations recovers up to 92% of simulated lenses with 100% purity, but only achieves 50% completeness with 24% purity on real Euclid data. By augmenting training data with real Euclid lenses and non-lenses, completeness improves by 25–30% in terms of the expected yield of discoverable lenses in the Euclid Data Release 1 and the full Euclid Wide Survey. Roughly 20% of this improvement comes from the inclusion of real lenses in the training data, while 5–10% comes from exposure to a more diverse set of non-lenses and false positives from Q1. We show that the most effective lens-finding strategy for real-world performance combines the diversity of simulations with the fidelity of real lenses. This hybrid approach establishes a clear methodology for maximising lens discoveries in future data releases from Euclid and will likely also be applicable to other surveys such as the Vera Rubin Observatory’s Legacy Survey of Space and Time.

Authors 96

1. N.E.P. Lines

   University of Portsmouth

   Affiliation as printed

   Institute of Cosmology and Gravitation, University of Portsmouth

2. Thomas E. Collett

   University of Portsmouth

   Affiliation as printed

   Institute of Cosmology and Gravitation, University of Portsmouth

3. Philip Holloway

   University of Portsmouth

   Affiliation as printed

   Institute of Cosmology and Gravitation, University of Portsmouth

4. K Rojas

   FHNW University of Applied Sciences and Arts Northwestern Switzerland

   Affiliation as printed

   University of Applied Sciences and Arts of Northwestern Switzerland, School of Computer Science

5. S. Schuldt

   National Institute for Astrophysics · University of Milan

   Affiliation as printed

   Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano

   INAF-IASF Milano

6. R. B. Metcalf

   Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics · University of Bologna

   Affiliation as printed

   Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna

   INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

7. Tian Li

   University of Portsmouth

   Affiliation as printed

   Institute of Cosmology and Gravitation, University of Portsmouth

8. A. Verma

   University of Oxford

   Affiliation as printed

   Department of Physics, Oxford University

9. Giulia Despali

   Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics · Istituto Nazionale di Fisica Nucleare, Sezione di Bologna · University of Bologna

   Affiliation as printed

   Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna

   INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

   INFN-Sezione di Bologna

10. F. Courbin

    Institut de Ciències del Cosmos · Universitat de Barcelona · Institució Catalana de Recerca i Estudis Avançats · Consejo Superior de Investigaciones Científicas · Institute of Space Sciences

    Affiliation as printed

    Institució Catalana de Recerca i Estudis Avançats (ICREA)

    Institut de Ciencies de l’Espai (IEEC-CSIC), Campus UAB

    Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB)

11. R. Gavazzi

    Centre National de la Recherche Scientifique · Institut d'Astrophysique de Paris · Sorbonne Université · Aix-Marseille Université

    Affiliation as printed

    Aix-Marseille Université, CNRS, CNES, LAM

    Institut d’Astrophysique de Paris, UMR 7095, CNRS, and Sorbonne Université

12. C. Tortora

    National Institute for Astrophysics · Astronomical Observatory of Capodimonte

    Affiliation as printed

    INAF-Osservatorio Astronomico di Capodimonte

13. B. Clément

    École Polytechnique Fédérale de Lausanne

    Affiliation as printed

    Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny

    SCITAS, Ecole Polytechnique Fédérale de Lausanne (EPFL)

14. N. Aghanim

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut d'Astrophysique Spatiale

    Affiliation as printed

    Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale

15. B Altieri

    European Space Agency · European Space Astronomy Centre

    Affiliation as printed

    ESAC/ESA

16. Luca Amendola

    Heidelberg University

    Affiliation as printed

    Institut für Theoretische Physik, University of Heidelberg

17. Stefano Andreon

    National Institute for Astrophysics · Brera Astronomical Observatory

    Affiliation as printed

    INAF-Osservatorio Astronomico di Brera

18. N. Auricchio

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

19. C. Baccigalupi

    Scuola Internazionale Superiore di Studi Avanzati · National Institute for Astrophysics · Trieste Astronomical Observatory · Istituto Nazionale di Fisica Nucleare, Sezione di Trieste · Institute for Fundamental Physics of the Universe

    Affiliation as printed

    IFPU, Institute for Fundamental Physics of the Universe

    INAF-Osservatorio Astronomico di Trieste

    INFN, Sezione di Trieste

    SISSA, International School for Advanced Studies

20. Marco Baldi

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics · Istituto Nazionale di Fisica Nucleare, Sezione di Bologna · University of Bologna

    Affiliation as printed

    Dipartimento di Fisica e Astronomia, Università di Bologna

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

    INFN-Sezione di Bologna

21. A. Balestra

    National Institute for Astrophysics · Osservatorio Astronomico di Padova

    Affiliation as printed

    INAF-Osservatorio Astronomico di Padova

22. S. Bardelli

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

23. P. Battaglia

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

24. A. Biviano

    National Institute for Astrophysics · Trieste Astronomical Observatory · Institute for Fundamental Physics of the Universe

    Affiliation as printed

    IFPU, Institute for Fundamental Physics of the Universe

    INAF-Osservatorio Astronomico di Trieste

25. E. Branchini

    National Institute for Astrophysics · University of Genoa · Istituto Nazionale di Fisica Nucleare, Sezione di Genova · Brera Astronomical Observatory

    Affiliation as printed

    Dipartimento di Fisica, Università di Genova

    INAF-Osservatorio Astronomico di Brera

    INFN-Sezione di Genova

26. M. Brescia

    National Institute for Astrophysics · University of Naples Federico II · Astronomical Observatory of Capodimonte

    Affiliation as printed

    Department of Physics “E. Pancini”, University Federico II

    INAF-Osservatorio Astronomico di Capodimonte

27. S. Camera

    National Institute for Astrophysics · Istituto Nazionale di Fisica Nucleare, Sezione di Torino · University of Turin · Osservatorio Astrofisico di Torino

    Affiliation as printed

    Dipartimento di Fisica, Università degli Studi di Torino

    INAF-Osservatorio Astrofisico di Torino

    INFN-Sezione di Torino

28. G Cañas-Herrera

    Leiden University · University of Edinburgh · Royal Observatory · Leiden Observatory

    Affiliation as printed

    Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill

    Leiden Observatory, Leiden University

29. V. Capobianco

    National Institute for Astrophysics · Osservatorio Astrofisico di Torino

    Affiliation as printed

    INAF-Osservatorio Astrofisico di Torino

30. J. Carretero

    Universitat Autònoma de Barcelona · Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas · Port d'Informació Científica

    Affiliation as printed

    Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT)

    Port d’Informació Científica, Campus UAB

31. M Castellano

    National Institute for Astrophysics · Astronomical Observatory of Rome

    Affiliation as printed

    INAF-Osservatorio Astronomico di Roma

32. G. Castignani

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

33. S. Cavuoti

    National Institute for Astrophysics · Istituto Nazionale di Fisica Nucleare · Istituto Nazionale di Fisica Nucleare, Sezione di Napoli · Astronomical Observatory of Capodimonte

    Affiliation as printed

    INAF-Osservatorio Astronomico di Capodimonte

    INFN section of Naples

34. A. Cimatti

    University of Bologna

    Affiliation as printed

    Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna

35. C Colodro-Conde

    Instituto de Astrofísica de Canarias

    Affiliation as printed

    Instituto de Astrofísica de Canarias

36. G. Congedo

    University of Edinburgh · Royal Observatory

    Affiliation as printed

    Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill

37. Christopher J. Conselice

    University of Manchester

    Affiliation as printed

    Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester

38. L. Conversi

    European Space Agency · European Space Astronomy Centre · European Space Research Institute

    Affiliation as printed

    ESAC/ESA

    European Space Agency/ESRIN

39. Y. Copin

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Lyon 1 Université · Institut de Physique des 2 Infinis de Lyon

    Affiliation as printed

    Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822

40. Hélène M. Courtois

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Institut de Physique des 2 Infinis de Lyon

    Affiliation as printed

    UCB Lyon 1, CNRS/IN2P3, IUF, IP2I Lyon

41. Maureen Cropper

    University College London

    Affiliation as printed

    Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking

42. Hubert Degaudenzi

    University of Geneva

    Affiliation as printed

    Department of Astronomy, University of Geneva

43. G. De Lucia

    National Institute for Astrophysics · Trieste Astronomical Observatory

    Affiliation as printed

    INAF-Osservatorio Astronomico di Trieste

44. Herve A. Dole

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut d'Astrophysique Spatiale

    Affiliation as printed

    Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale

45. F. Dubath

    University of Geneva

    Affiliation as printed

    Department of Astronomy, University of Geneva

46. X. Dupac

    European Space Agency · European Space Astronomy Centre

    Affiliation as printed

    ESAC/ESA

47. S. Dusini

    Istituto Nazionale di Fisica Nucleare, Sezione di Padova · Istituto Nazionale di Fisica Nucleare

    Affiliation as printed

    INFN-Padova

48. Anne Ealet

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Lyon 1 Université · Institut de Physique des 2 Infinis de Lyon

    Affiliation as printed

    Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822

49. S. Escoffier

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Aix-Marseille Université · Centre de physique des particules de Marseille

    Affiliation as printed

    Aix-Marseille Université, CNRS/IN2P3, CPPM

50. R Farinelli

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

51. F Faustini

    National Institute for Astrophysics · Agenzia Spaziale Italiana · Astronomical Observatory of Rome

    Affiliation as printed

    INAF-Osservatorio Astronomico di Roma

    Space Science Data Center, Italian Space Agency

52. S. Ferriol

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Lyon 1 Université · Institut de Physique des 2 Infinis de Lyon

    Affiliation as printed

    Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822

53. Fabio Finelli

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics · Istituto Nazionale di Fisica Nucleare, Sezione di Bologna

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

    INFN-Bologna

54. M. Frailis

    National Institute for Astrophysics · Trieste Astronomical Observatory

    Affiliation as printed

    INAF-Osservatorio Astronomico di Trieste

55. Enrico Franceschi

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

56. M. Fumana

    National Institute for Astrophysics

    Affiliation as printed

    INAF-IASF Milano

57. Samuele Galeotta

    National Institute for Astrophysics · Trieste Astronomical Observatory

    Affiliation as printed

    INAF-Osservatorio Astronomico di Trieste

58. Koshy George

    Ludwig-Maximilians-Universität München

    Affiliation as printed

    University Observatory, LMU Faculty of Physics

59. Bryan R. Gillis

    University of Edinburgh · Royal Observatory

    Affiliation as printed

    Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill

60. C. Giocoli

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics · Istituto Nazionale di Fisica Nucleare, Sezione di Bologna

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

    INFN-Sezione di Bologna

61. P Gómez-Álvarez

    European Space Agency · European Space Astronomy Centre

    Affiliation as printed

    ESAC/ESA

    FRACTAL S.L.N.E., calle Tulipán 2

62. Javier Graciá-Carpio

    Max Planck Institute for Extraterrestrial Physics

    Affiliation as printed

    Max Planck Institute for Extraterrestrial Physics

63. A. Grazian

    National Institute for Astrophysics · Osservatorio Astronomico di Padova

    Affiliation as printed

    INAF-Osservatorio Astronomico di Padova

64. Frank U. Grupp

    Ludwig-Maximilians-Universität München · Max Planck Institute for Extraterrestrial Physics

    Affiliation as printed

    Max Planck Institute for Extraterrestrial Physics

    Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München

65. S. V. H. Haugan

    University of Oslo

    Affiliation as printed

    Institute of Theoretical Astrophysics, University of Oslo

66. W. Holmes

    Jet Propulsion Laboratory

    Affiliation as printed

    Jet Propulsion Laboratory, California Institute of Technology

67. I. Hook

    Lancaster University

    Affiliation as printed

    Department of Physics, Lancaster University

68. F. Hormuth
    Affiliation as printed

    Felix Hormuth Engineering

69. Allan Hornstrup

    Technical University of Denmark

    Affiliation as printed

    Cosmic Dawn Center (DAWN)

    Technical University of Denmark

70. K. Jahnkę

    Max Planck Institute for Astronomy

    Affiliation as printed

    Max-Planck-Institut für Astronomie

71. M. Jhabvala

    Goddard Space Flight Center

    Affiliation as printed

    NASA Goddard Space Flight Center

72. B Joachimi

    University College London

    Affiliation as printed

    Department of Physics and Astronomy, University College London

73. Elina Keihänen

    Helsinki Institute of Physics

    Affiliation as printed

    Department of Physics and Helsinki Institute of Physics

74. Smaïn Kermiche

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Aix-Marseille Université · Centre de physique des particules de Marseille

    Affiliation as printed

    Aix-Marseille Université, CNRS/IN2P3, CPPM

75. A. Kiessling

    Jet Propulsion Laboratory

    Affiliation as printed

    Jet Propulsion Laboratory, California Institute of Technology

76. Bogna Kubik

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Lyon 1 Université · Institut de Physique des 2 Infinis de Lyon

    Affiliation as printed

    Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822

77. M. Kümmel

    Ludwig-Maximilians-Universität München

    Affiliation as printed

    Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München

78. Hannu Kurki-Suonio

    University of Helsinki · Helsinki Institute of Physics

    Affiliation as printed

    Department of Physics

    Helsinki Institute of Physics, Gustaf Hällströmin katu 2, University of Helsinki

79. Amandine M. C. Le Brun

    Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Sorbonne Université · Observatoire de Paris · Laboratoire d'Étude de l'Univers et des Phénomènes Extrêmes

    Affiliation as printed

    Laboratoire d’etude de l’Univers et des phenomenes eXtremes, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS

80. S. Ligori

    National Institute for Astrophysics · Osservatorio Astrofisico di Torino

    Affiliation as printed

    INAF-Osservatorio Astrofisico di Torino

81. Per Barth Lilje

    University of Oslo

    Affiliation as printed

    Institute of Theoretical Astrophysics, University of Oslo

82. V. Lindholm

    University of Helsinki · Helsinki Institute of Physics

    Affiliation as printed

    Department of Physics

    Helsinki Institute of Physics, Gustaf Hällströmin katu 2, University of Helsinki

83. Ivan Lloro

    SKA Observatory

    Affiliation as printed

    SKAO, Jodrell Bank, Lower Withington

84. Gabriele Mainetti

    Centre National de la Recherche Scientifique · Centre de Calcul de l’Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Centre de Calcul de l’IN2P3/CNRS

85. Davide Maino

    National Institute for Astrophysics · University of Milan · Istituto Nazionale di Fisica Nucleare, Sezione di Milano

    Affiliation as printed

    Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano

    INAF-IASF Milano

    INFN-Sezione di Milano

86. E. Maiorano

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

87. O. Mansutti

    National Institute for Astrophysics · Trieste Astronomical Observatory

    Affiliation as printed

    INAF-Osservatorio Astronomico di Trieste

88. S. Marcin

    FHNW University of Applied Sciences and Arts Northwestern Switzerland

    Affiliation as printed

    University of Applied Sciences and Arts of Northwestern Switzerland, School of Computer Science

89. O. Marggraf

    University of Bonn

    Affiliation as printed

    Universität Bonn, Argelander-Institut für Astronomie

90. N. Martinet

    Centre National de la Recherche Scientifique · Aix-Marseille Université

    Affiliation as printed

    Aix-Marseille Université, CNRS, CNES, LAM

91. F. Marulli

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics · Istituto Nazionale di Fisica Nucleare, Sezione di Bologna · University of Bologna

    Affiliation as printed

    Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

    INFN-Sezione di Bologna

92. R. J. Massey

    Durham University

    Affiliation as printed

    Department of Physics, Institute for Computational Cosmology, Durham University

93. Eduardo Medinaceli

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna

94. S. Mei

    Centre National de la Recherche Scientifique · Institut National de Physique Nucléaire et de Physique des Particules · Université Paris Cité · Centre Pierre Binétruy

    Affiliation as printed

    CNRS-UCB International Research Laboratory, Centre Pierre Binétruy, IRL2007, CPB-IN2P3

    Université Paris Cité, CNRS, Astroparticule et Cosmologie

95. M. Melchior

    FHNW University of Applied Sciences and Arts Northwestern Switzerland

    Affiliation as printed

    University of Applied Sciences and Arts of Northwestern Switzerland, School of Engineering

96. Y Mellier

    Centre National de la Recherche Scientifique · Institut d'Astrophysique de Paris · Sorbonne Université

    Affiliation as printed

    Institut d’Astrophysique de Paris

    Institut d’Astrophysique de Paris, UMR 7095, CNRS, and Sorbonne Université