<i>Euclid</i> : Discovery of bright <i>z</i> ≃ 7 Lyman-break galaxies in UltraVISTA and <i>Euclid</i> COSMOS

We present a search for z ≃ 7 Lyman-break galaxies using the 1.72 deg 2 near-infrared (NIR) UltraVISTA survey in the COSMOS field, reaching 5 σ depths in Y of 26.2. We incorporated deep Euclid optical and Euclid + Spitzer NIR imaging for a full spectral energy distribution (SED) fitting analysis. We found 289 candidate galaxies at 6.5 ≤ z ≤ 7.5 covering −22.6 ≤ M UV ≤ −20.2, faint enough to overlap with Hubble Space Telescope studies. We conducted a separate selection by including complementary Euclid performance verification imaging (reaching 5 σ depths of 26.3), yielding 140 galaxies in 0.65 deg 2 , with 38 sources unique to this sample. We computed the rest-frame UV luminosity function (UV LF) from our samples, extending below the knee ( M ∗ = 21.14 +0.28 −0.25 ). We find that the shape of the UV LF is consistent with both a Schechter function and a double power law (DPL) at the magnitudes probed by this sample, with a DPL preferred at M UV &lt; −22.5 when bright-end results are included. The UltraVISTA + Euclid sample provides a clean measurement of the LF due to the overlapping NIR filters identifying molecular absorption features in the SEDs of ultra-cool dwarf interlopers, and additional faint galaxies were recovered. A comparison with JWST LFs at z &gt; 7 suggests a gentle evolution in the bright-end slope, although this is limited by a lack of robust bright-end measurements at z &gt; 9. We forecast that in the Euclid Deep Fields, the removal of contaminant ultra-cool dwarfs as point sources will be possible at J E &lt; 24.5. Finally, we present a high-equivalent-width Lyman- α emitter candidate identified by combining HSC, VISTA, and Euclid broadband photometry, highlighting the synergistic power these instruments will have in the Euclid Auxiliary Fields for identifying extreme sources in the epoch of reionisation.

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Journal
Astronomy and Astrophysics
Published
2026-02-03
DOI
https://doi.org/10.1051/0004-6361/202557508
Primary Topic
Astronomy and Astrophysical Research
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article
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0.00

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article

Euclid : Discovery of bright z ≃ 7 Lyman-break galaxies in UltraVISTA and Euclid COSMOS

M Viel, K. George, F Raison, R. P. Saglia et al.
Astronomy and Astrophysics
Astronomy and Astrophysical Research
article

Euclid : Discovery of bright z ≃ 7 Lyman-break galaxies in UltraVISTA and Euclid COSMOS

M Viel, K. George, F Raison, R. P. Saglia, V. Lindholm, F. Pasian, G. Riccio, Chris Carbone, M. Schirmer, J. Martín-Fleitas, W. Holmes, G. Zamorani, G. Meylan, I Tereno, I. Hook, D Sapone, F. Dubath, K. I. Caputi, R Nakajima, B. Joachimi, J. Steinwagner, S Ferriol, F. Torradeflot, Y. Copin, F Courbin, M. Jhabvala, E Maiorano, L. A. Popa, S. Mei, O Marggraf, L Conversi, F Faustini, J. R. Weaver, V. Capobianco, V. Scottez, C. Baccigalupi, T. Schrabback, L. Gabarra, A. Kiessling, A. Grazian, S. Pires, G Polenta, R. Massey, T. Vassallo, I. Tutusaus, M. Cropper, R. Toledo-Moreo, J. Hoar, M. Moresco, K Pedersen, M. Meneghetti, G. De Lucia, L. Valenziano, N Tessore, J. Valiviita, P. B. Lilje, Christopher J. Conselice, Henk Hoekstra, C. Colodro-Conde, A. Biviano, H. Degaudenzi, A. Cimatti, H. M. Courtois, L. Moscardini, B. Milvang-Jensen, P Schneider, C Sirignano, M Frailis, J. Carretero, M. Martinelli, S. Escoffier, C. Padilla Aranda, E Keihänen, B. Gillis, S. Dusini, S. M. Wilkins, A. Hornstrup, E. Medinaceli, P. A. Oesch, F. M. Zerbi, E. Branchini, M. Farina, S. Camera, L. Guzzo, Sergio Serrano, G. Seidel, F. Grupp, R. Farinelli, J. Weller, Eduardo Bañados, E. Franceschi, P. Tallada-Crespí, K Jahnke, ENRIQUE GAZTAÑAGA, M. Brescia, Pardis Simon, Y. Mellier, M. Kilbinger, G Cañas-Herrera, J. Gracia-Carpio, A Secroun, Z. Sakr, R. A. A. Bowler, G. Congedo, Da-Ming Yang, M. Fumana, S. Andreon, M. Melchior, A. N. Taylor, A da Silva, G. Castignani, E. Romelli, S Galeotta, Marion Poncet, E Zucca, H. I. Teplitz, S. Kermiche, S. -M. Niemi, M. J. Jarvis, S. Desai, Sune Toft, M. Castellano, C. Padilla, O. Mansutti, Paul H. Holloway, N. Martinet, C. Giocoli, A Veropalumbo, E. Rossetti, G. Mainetti, A.M.C Le Brun, R. G. Varadaraj, M. Kümmel, S Cavuoti, L. Pozzetti, N. Auricchio, J. Steinwagner, Yun Wang, Pedro G. Ferreira, L. Stančo, M. Roncarelli, M Kunz, M. Baldi, J Rhodes, B. Sartoris, V. Pettorino, C Neissner, A Amara, X. Dupac, L. Popa, S Bardelli, S. V. H. Haugan, E. Merlin, H. Kurki‐Suonio, P. Fosalba, F. Hormuth, A. N. Taylor, B. Kubik, I. Lloro, S. Paltani, N. Fourmanoit, A. Mora, C. A. J. Duncan, S Ligori, A. Renzi
article en

Abstract

We present a search for z ≃ 7 Lyman-break galaxies using the 1.72 deg 2 near-infrared (NIR) UltraVISTA survey in the COSMOS field, reaching 5 σ depths in Y of 26.2. We incorporated deep Euclid optical and Euclid + Spitzer NIR imaging for a full spectral energy distribution (SED) fitting analysis. We found 289 candidate galaxies at 6.5 ≤ z ≤ 7.5 covering −22.6 ≤ M UV ≤ −20.2, faint enough to overlap with Hubble Space Telescope studies. We conducted a separate selection by including complementary Euclid performance verification imaging (reaching 5 σ depths of 26.3), yielding 140 galaxies in 0.65 deg 2 , with 38 sources unique to this sample. We computed the rest-frame UV luminosity function (UV LF) from our samples, extending below the knee ( M ∗ = 21.14 +0.28 −0.25 ). We find that the shape of the UV LF is consistent with both a Schechter function and a double power law (DPL) at the magnitudes probed by this sample, with a DPL preferred at M UV &lt; −22.5 when bright-end results are included. The UltraVISTA + Euclid sample provides a clean measurement of the LF due to the overlapping NIR filters identifying molecular absorption features in the SEDs of ultra-cool dwarf interlopers, and additional faint galaxies were recovered. A comparison with JWST LFs at z &gt; 7 suggests a gentle evolution in the bright-end slope, although this is limited by a lack of robust bright-end measurements at z &gt; 9. We forecast that in the Euclid Deep Fields, the removal of contaminant ultra-cool dwarfs as point sources will be possible at J E &lt; 24.5. Finally, we present a high-equivalent-width Lyman- α emitter candidate identified by combining HSC, VISTA, and Euclid broadband photometry, highlighting the synergistic power these instruments will have in the Euclid Auxiliary Fields for identifying extreme sources in the epoch of reionisation.

Astronomy and AstrophysicsVol. 707
Université Claude Bernard Lyon 1 (FR), University of Geneva (CH), Institució Catalana de Recerca i Estudis Avançats (ES), Leiden University (NL), California Institute of Technology (US), University of Copenhagen (DK), Centre National de la Recherche Scientifique (FR), Goddard Space Flight Center (US), University of Hawaii System (US), Jet Propulsion Laboratory (US), Université Toulouse III - Paul Sabatier (FR), University of Bonn (DE), Scuola Internazionale Superiore di Studi Avanzati (IT), University of Padua (IT), University of Lisbon (PT), University of Waterloo (CA), University of Sussex (GB), University of Groningen (NL), Université Fédérale de Toulouse Midi-Pyrénées (FR), Lyon College (US), Université Catholique de Lille (FR), Perimeter Institute (CA), University of Oslo (NO), Institute for High Energy Physics (ES), University of Milan (IT), Universität Innsbruck (AT), University of Saint Joseph (US), Université Paris Cité (FR), Aix-Marseille Université (FR), Heidelberg University (DE), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris Sciences et Lettres (FR), Université Paris-Saclay (FR), Centre National d'Études Spatiales (FR), Helsinki Institute of Physics (FI), Astronomical Observatory of Rome (IT), Trieste Astronomical Observatory (IT), Institut d'Astrophysique de Paris (FR), Astronomical Observatory of Capodimonte (IT), European Space Agency (FR), Laboratoire AstroParticule et Cosmologie (FR), Brera Astronomical Observatory (IT), University of Surrey (GB), FHNW University of Applied Sciences and Arts Northwestern Switzerland (CH), United Kingdom Space Agency (GB), Universidad Politécnica de Cartagena (ES), Sorbonne Université (FR), University of Oxford (GB), Park University (US), Osservatorio astronomico di Bologna (IT), Astrophysique, Instrumentation et Modélisation (FR), Institute of Astrophysics and Space Sciences (PT), Max Planck Institute for Extraterrestrial Physics (DE), Institut d'Estudis Espacials de Catalunya (ES), Kavli Institute for Particle Astrophysics and Cosmology (US), Istituto Nazionale di Fisica Nucleare, Sezione di Torino (IT), Institute for Space Astrophysics and Planetology (IT), Institut d'Astrophysique Spatiale (FR), International University of Beirut (LB), Institut Català de Ciències del Clima (ES), Istituto Nazionale di Fisica Nucleare, Sezione di Padova (IT), Osservatorio Astrofisico di Torino (IT), Royal Observatory (GB), SKA Observatory (GB), Istituto Nazionale di Fisica Nucleare, Sezione di Napoli (IT), Max Planck Institute for Astronomy (DE), Institute of Space Sciences (ES), Laboratoire de Physique Théorique (FR), DAWN Center for Independent Living (US), Federico II University Hospital (IT), Institute of Theoretical Physics (CN), Istituto Nazionale di Fisica Nucleare, Sezione di Genova (IT), CEA Paris-Saclay (FR), Naples Anesthesia & Physician Associates (US), Instituto de Astrofísica de Canarias (ES), Felix Scholarship (GB), Astronomical Institute of the Slovak Academy of Sciences (SK), Istituto Nazionale di Fisica Nucleare, Sezione di Milano (IT), Institute of Space Science - INFLPR Subsidiary (RO), Computing Center (RU), Centre de Calcul de l’Institut National de Physique Nucléaire et de Physique des Particules (FR), Engineering Science Analysis (United States) (US), Istituto Nazionale di Fisica Nucleare, Sezione di Bologna (IT), Port d'Informació Científica (ES), Istituto Nazionale di Fisica Nucleare, Sezione di Trieste (IT), Institute for Fundamental Physics of the Universe (IT), Astronomical Observatory (RS), St. Joseph Medical Center (US), Istituto Nazionale di Fisica Nucleare, Sezione di Roma I (IT), Osservatorio Astronomico di Padova (IT), European Space Research Institute (IT), Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (ES), Institut de Recherche en Astrophysique et Planétologie (FR), Infrared Processing and Analysis Center (US), Osservatorio di Astrofisica e Scienza dello Spazio, European Space Research and Technology Centre (NL), University College London (GB), UK Astronomy Technology Centre (GB), École Polytechnique Fédérale de Lausanne (CH), University of Turin (IT), University of Portsmouth (GB), Massachusetts Institute of Technology (US), Lancaster University (GB), University of Chile (CL), Heidelberg Institute for Theoretical Studies (DE), Ludwig-Maximilians-Universität München (DE), University of Genoa (IT), University of the Western Cape (ZA), National Institute for Astrophysics (IT), University of Bologna (IT), Technical University of Denmark (DK)
National Aeronautics and Space Administration, Princeton University, UK Research and Innovation, European Space Agency, National Research Foundation, Ministry of Education, Culture, Sports, Science and Technology, Danmarks Grundforskningsfond, Academia Sinica, Cabinet Office, Government of Japan, Magyar Tudományos Akadémia, Agenzia Spaziale Italiana, European Southern Observatory, National Astronomical Observatory of Japan, High Energy Accelerator Research Organization, Agenția Spațială Română, Norsk Romsenter, Toray Science Foundation, Science and Technology Facilities Council, Japan Society for the Promotion of Science, Fundação para a Ciência e a Tecnologia, Japan Science and Technology Agency
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