Euclid: Early Release Observations – Unveiling the morphology of two Milky Way globular clusters out to their periphery

Creators: Massari, D.¹; Dalessandro, E.¹; Erkal, D.²; Balbinot, E.^{3, 4}; Bovy, J.⁵; McDonald, I.⁶; Ferguson, A. M. N.⁷; Larsen, S. S.⁸; Lançon, A.⁹; Annibali, F.¹; Goldman, B.^{10, 9}; Kuzma, P. B.^{7, 11}; Voggel, K.⁹; Saifollahi, T.^{4, 9}; Cuillandre, J.-C.¹²; Schirmer, M.¹³; Kluge, M.¹⁴; Altieri, B.¹⁵; Amara, A.²; Andreon, S.¹⁶; Auricchio, N.¹; Baldi, M.^{17, 1, 18}; Balestra, A.¹⁹; Bardelli, S.¹; Basset, A.²⁰; Bender, R.^{14, 21}; Bonino, D.²²; Branchini, E.^{23, 24, 16}; Brescia, M.^{25, 26, 27}; Brinchmann, J.²⁸; Camera, S.^{29, 30, 22}; Candini, G. P.³¹; Capobianco, V.²²; Carbone, C.³²; Carlberg, R. G.⁵; Carretero, J.³³; Casas, S.³⁴; Castellano, M.³⁵; Cavuoti, S.^{26, 27}; Cimatti, A.¹⁷; Congedo, G.⁷; Conselice, C. J.⁶; Conversi, L.^{36, 15}; Copin, Y.³⁷; Corcione, L.²²; Courbin, F.³⁸; Courtois, H. M.³⁹; Degaudenzi, H.⁴⁰; Dinis, J.⁴¹; Dubath, F.⁴⁰; Dupac, X.¹⁵; Dusini, S.⁴²; Fabricius, M.^{14, 21}; Farina, M.⁴³; Farrens, S.¹²; Ferriol, S.³⁷; Frailis, M.⁴⁴; Franceschi, E.¹; Garilli, B.³²; Gillis, B.⁷; Giocoli, C.^{1, 18}; Grazian, A.¹⁹; Guzzo, L.^{45, 16, 46}; Hoar, J.¹⁵; Hoekstra, H.³; Holliman, M. S.⁷; Holmes, W.⁴⁷; Hook, I.⁴⁸; Hormuth, F.; Hornstrup, A.^{49, 50}; Hudelot, P.^{51, 52}; Jahnke, K.¹³; Keihänen, E.⁵³; Kermiche, S.⁵⁴; Kiessling, A.⁴⁷; Kitching, T.³¹; Kohley, R.¹⁵; Kubik, B.³⁷; Kümmel, M.²¹; Kunz, M.⁴⁰; Kurki-Suonio, H.^{53, 55}; Ligori, S.²²; Lilje, P. B.⁵⁶; Lindholm, V.^{53, 55}; Lloro, I.⁵⁷; Maino, D.^{45, 32, 46}; Maiorano, E.¹; Mansutti, O.⁴⁴; Marggraf, O.⁵⁸; Markovic, K.⁴⁷; Martinet, N.⁵⁹; Marulli, F.^{17, 1, 18}; Massey, R.⁶⁰; Maurogordato, S.⁶¹; Medinaceli, E.¹; Mei, S.⁶²; Mellier, Y.^{51, 52}; Meneghetti, M.^{1, 18}; Meylan, G.³⁸; Moresco, M.^{17, 1}; Moscardini, L.^{17, 1, 18}; Munari, E.⁴⁴; Nakajima, R.¹⁷; Nichol, R. C.²; Niemi, S.-M.⁶³; Padilla, C.³³; Paltani, S.⁴⁰; Pasian, F.⁴⁴; Pedersen, K.⁶⁴; Percival, W. J.^{65, 66}; Pettorino, V.⁶³; Pires, S.¹²; Polenta, G.⁶⁷; Poncet, M.²⁰; Popa, L. A.⁶⁸; Pozzetti, L.¹; Racca, G. D.⁶³; Raison, F.¹⁴; Rebolo, R.^{69, 70}; Renzi, A.^{71, 42}; Rhodes, J.⁴⁷; Riccio, G.²⁶; Rix, H.-W.¹³; Romelli, E.⁴⁴; Roncarelli, M.¹; Rossetti, E.¹⁷; Saglia, R.^{21, 14}; Sapone, D.⁷²; Sartoris, B.^{21, 44}; Schneider, P.⁵⁸; Schrabback, T.⁷³; Secroun, A.⁵⁴; Seidel, G.¹³; Seiffert, M.⁴⁷; Serrano, S.^{74, 75, 76}; Sirignano, C.^{71, 42}; Sirri, G.¹⁸; Skottfelt, J.⁷⁷; Stanco, L.⁴²; Tallada-Crespí, P.⁷⁸; Teplitz, H. I.⁷⁹; Tereno, I.⁴¹; Toledo-Moreo, R.⁸⁰; Torradeflot, F.⁷⁸; Tutusaus, I.⁸¹; Valenziano, L.^{1, 18}; Vassallo, T.^{21, 44}; Veropalumbo, A.^{16, 24}; Wang, Y.⁷⁹; Weller, J.^{21, 14}; Zacchei, A.^{44, 82}; Zamorani, G.¹; Zoubian, J.⁵⁴; Zucca, E.¹; Bolzonella, M.¹; Burigana, C.^{83, 18}; Morris, P. W.⁸⁴; Scottez, V.^{51, 85}; Simon, P.⁵⁸; Martín-Fleitas, J.⁸⁶; Scott, D.⁸⁷

1. INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129, Bologna, Italy
2. University of Surrey
3. Leiden University
4. University of Groningen
5. University of Toronto
6. University of Manchester
7. University of Edinburgh
8. Radboud University Nijmegen
9. Observatory of Strasbourg
10. International Space University
11. National Astronomical Observatory of Japan
12. University of Paris
13. Max Planck Institute for Astronomy
14. Max Planck Institute for Extraterrestrial Physics
15. European Space Astronomy Centre
16. Brera Astronomical Observatory
17. University of Bologna
18. INFN Sezione di Bologna
19. Osservatorio Astronomico di Padova
20. Centre National d'Études Spatiales
21. Ludwig-Maximilians-Universität München
22. Osservatorio Astrofisico di Torino
23. University of Genoa
24. INFN Sezione di Genova
25. University of Naples Federico II
26. Astronomical Observatory of Capodimonte
27. INFN Sezione di Napoli
28. University of Porto
29. University of Turin
30. INFN Sezione di Torino
31. University College London
32. Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano
33. Institute for High Energy Physics
34. RWTH Aachen University
35. INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00078, Monteporzio Catone, Italy
36. European Space Research Institute
37. Claude Bernard University Lyon 1
38. École Polytechnique Fédérale de Lausanne
39. UCB Lyon 1, CNRS/IN2P3, IUF, IP2I Lyon, 4 Rue Enrico Fermi, 69622, Villeurbanne, France
40. University of Geneva
41. University of Lisbon
42. INFN Sezione di Padova
43. Institute for Space Astrophysics and Planetology
44. Trieste Astronomical Observatory
45. University of Milan
46. INFN Sezione di Milano
47. Jet Propulsion Lab
48. Lancaster University
49. Technical University of Denmark
50. University of Copenhagen
51. Institut d'Astrophysique de Paris
52. Sorbonne University
53. University of Helsinki
54. Center for Particle Physics of Marseilles
55. Helsinki Institute of Physics
56. University of Oslo
57. Netherlands Institute for Radio Astronomy
58. University of Bonn
59. Aix-Marseille Université, CNRS, CNES, LAM, Marseille, France
60. Durham University
61. Lagrange Laboratory
62. Astroparticle and Cosmology Laboratory
63. European Space Research and Technology Centre
64. Aarhus University
65. University of Waterloo
66. Perimeter Institute
67. Agenzia Spaziale Italiana
68. Institute of Space Science
69. Instituto de Astrofísica de Canarias
70. University of La Laguna
71. University of Padua
72. University of Chile
73. Universität Innsbruck
74. Institut d'Estudis Espacials de Catalunya
75. Institute of Space Sciences
76. Satlantis, University Science Park, Sede Bld, 48940, Leioa-Bilbao, Spain
77. The Open University
78. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
79. Infrared Processing and Analysis Center
80. Polytechnic University of Cartagena
81. Research Institute in Astrophysics and Planetology
82. Institute for Fundamental Physics of the Universe
83. National Institute for Astrophysics
84. California Institute of Technology
85. Groupe Institut supérieur d'agriculture de Lille
86. Aurora Technology for European Space Agency (ESA), Camino Bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692, Madrid, Spain
87. University of British Columbia

Abstract

As part of the Euclid Early Release Observations (ERO) programme, we analysed deep, wide-field imaging from the VIS and NISP instruments of two Milky Way globular clusters (GCs), namely NGC 6254 (M10) and NGC 6397, to look for observational evidence of their dynamical interaction with the Milky Way. We searched for such an interaction in the form of structural and morphological features in the clusters' outermost regions, which would be suggestive of the development of tidal tails on scales larger than those sampled by the ERO data. From our multi-band photometric analysis, we obtained deep and well-behaved colour–magnitude diagrams that, in turn, enabled an accurate membership selection. The surface brightness profiles built from these samples of member stars are the deepest ever obtained for these two Milky Way GCs, reaching down to ∼30.0 mag/arcsec2, which is ∼1.5 mag/arcsec2 lower than before. The investigation of the two-dimensional density map of NGC 6254 reveals an elongated morphology of the cluster peripheries in the direction and with the amplitude predicted by N-body simulations of the cluster's dynamical evolution, at high statistical significance. We interpret this as strong evidence for the first detection of tidally induced morphological distortion around this cluster. The density map of NGC 6397 reveals a slightly elliptical morphology, in agreement with previous studies, which requires further investigation on larger scales to be properly interpreted. This ERO project thus demonstrates the power of Euclid in studying the outer regions of GCs at an unprecedented level of detail, thanks to the combination of the large field of view, high spatial resolution, and depth enabled by the telescope. Our results highlight the future Euclid survey as the ideal dataset for investigating GC tidal tails and stellar streams.

Copyright and License

© The Authors 2025. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

We are grateful to the anonymous referee for the invaluable feedback that improved the quality of the paper. DM thanks the Fundactión Jesús Serra visiting programme and the Instituto de Astrofísica de Canarias for hospitality. DM acknowledges financial support from the European Union – NextGenerationEU RRF M4C2 1.1 n: 2022HY2NSX. “CHRONOS: adjusting the clock(s) to unveil the CHRONO-chemo-dynamical Structure of the Galaxy” (PI: S. Cassisi). ED aknowledges financial support from the Fulbright Visiting Scholar program 2023. ED is also grateful for the warm hospitality of the Indiana University where part of this work was performed. AMNF acknowledges support from the UK STFC via grant ST/Y001281/1. IM acknowledges funding from UKRI/STFC through grants ST/T000414/1 and ST/X001229/1, and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101004214. AL acknowledges funding from Agence Nationale de la Recherche (France) under grant ANR-19-CE31-0022 This work has made use of the Early Release Observations (ERO) data from the Euclid mission of the European Space Agency (ESA), 2024, https://doi.org/10.57780/esa-qmocze3. The Euclid Consortium acknowledges the European Space Agency and a number of agencies and institutes that have supported the development of Euclid, in particular the Agenzia Spaziale Italiana, the Austrian Forschungsförderungsgesellschaft funded through BMK, the Belgian Science Policy, the Canadian Euclid Consortium, the Deutsches Zentrum für Luft-und Raumfahrt, the DTU Space and the Niels Bohr Institute in Denmark, the French Centre National d’Etudes Spatiales, the Fundação para a Ciência e a Tecnologia, the Hungarian Academy of Sciences, the Ministerio de Ciencia, Innovación y Universidades, the National Aeronautics and Space Administration, the National Astronomical Observatory of Japan, the Netherlandse Onderzoekschool Voor Astronomie, the Norwegian Space Agency, the Research Council of Finland, the Romanian Space Agency, the State Secretariat for Education, Research, and Innovation (SERI) at the Swiss Space Office (SSO), and the United Kingdom Space Agency. A complete and detailed list is available on the Euclid web site (http://www.euclid-ec.org).

Data Availability

Tables of the extracted photometry and positions are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/697/A8

Additional Information

This paper is published on behalf of the Euclid Consortium.

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