Euclid: The first statistical census of dusty and massive objects in the ERO/Perseus field^★

¹ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova Via Marzolo 8 35131 Padova, Italy
² INAF-Osservatorio Astronomico di Padova Via dell’Osservatorio 5 35122 Padova, Italy
³ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova Vicolo dell’Osservatorio 3 35122 Padova, Italy
⁴ Max-Planck-Institut für Astronomie Königstuhl 17 69117 Heidelberg, Germany
⁵ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna Via Piero Gobetti 93/3 40129 Bologna, Italy
⁶ Department of Astronomy, University of Massachusetts Amherst MA 01003, USA
⁷ School of Physics and Astronomy, Cardiff University, The Parade Cardiff CF24 3AA, UK
⁸ Institute of Cosmology and Gravitation, University of Portsmouth Portsmouth PO1 3FX, UK
⁹ Kapteyn Astronomical Institute, University of Groningen PO Box 800 9700 AV Groningen, The Netherlands
¹⁰ Cosmic Dawn Center (DAWN)
¹¹ Dipartimento di Fisica e Astronomia, Università di Bologna Via Gobetti 93/2 40129 Bologna, Italy
¹² Jeremiah Horrocks Institute, University of Central Lancashire Preston PR1 2HE, UK
¹³ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550 67000 Strasbourg, France
¹⁴ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale 91405 Orsay, France
¹⁵ ESAC/ESA, Camino Bajo del Castillo, s/n Urb. Villafranca del Castillo 28692 Villanueva de la Cañada Madrid, Spain
¹⁶ INAF-Osservatorio Astronomico di Brera Via Brera 28 20122 Milano, Italy
¹⁷ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM 91191 Gif-sur-Yvette, France
¹⁸ IFPU, Institute for Fundamental Physics of the Universe Via Beirut 2 34151 Trieste, Italy
¹⁹ INAF-Osservatorio Astronomico di Trieste Via G. B. Tiepolo 11 34143 Trieste, Italy
²⁰ INFN, Sezione di Trieste Via Valerio 2 34127 Trieste TS, Italy
²¹ SISSA, International School for Advanced Studies Via Bonomea 265 34136 Trieste TS, Italy
²² INFN-Sezione di Bologna Viale Berti Pichat 6/2 40127 Bologna, Italy
²³ Dipartimento di Fisica, Università di Genova Via Dodecaneso 33 16146 Genova, Italy
²⁴ INFN-Sezione di Genova Via Dodecaneso 33 16146 Genova, Italy
²⁵ Department of Physics “E. Pancini”, University Federico II Via Cinthia 6 80126 Napoli, Italy
²⁶ INAF-Osservatorio Astronomico di Capodimonte Via Moiariello 16 80131 Napoli, Italy
²⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP Rua das Estrelas PT4150-762 Porto, Portugal
²⁸ Faculdade de Ciências da Universidade do Porto Rua do Campo de Alegre 4150-007 Porto, Portugal
²⁹ Dipartimento di Fisica, Università degli Studi di Torino Via P. Giuria 1 10125 Torino, Italy
³⁰ INFN-Sezione di Torino Via P. Giuria 1 10125 Torino, Italy
³¹ INAF-Osservatorio Astrofisico di Torino Via Osservatorio 20 10025 Pino Torinese (TO), Italy
³² European Space Agency/ESTEC Keplerlaan 1 2201 AZ Noordwijk, The Netherlands
³³ Institute Lorentz, Leiden University Niels Bohrweg 2 2333 CA Leiden, The Netherlands
³⁴ Leiden Observatory, Leiden University Einsteinweg 55 2333 CC Leiden, The Netherlands
³⁵ INAF-IASF Milano Via Alfonso Corti 12 20133 Milano, Italy
³⁶ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) Avenida Complutense 40 28040 Madrid, Spain
³⁷ Port d’Informació Científica, Campus UAB C. Albareda s/n 08193 Bellaterra (Barcelona), Spain
³⁸ Institute for Theoretical Particle Physics and Cosmology (TTK), RWTH Aachen University 52056 Aachen, Germany
³⁹ INAF-Osservatorio Astronomico di Roma Via Frascati 33 00078 Monteporzio Catone, Italy
⁴⁰ INFN Section of Naples Via Cinthia 6 80126 Napoli, Italy
⁴¹ Institute for Astronomy, University of Hawaii 2680 Woodlawn Drive Honolulu HI 96822, USA
⁴² Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna Viale Berti Pichat 6/2 40127 Bologna, Italy
⁴³ Instituto de Astrofísica de Canarias Vía Láctea 38205 La Laguna Tenerife, Spain
⁴⁴ Institute for Astronomy, University of Edinburgh, Royal Observatory Blackford Hill Edinburgh EH9 3HJ, UK
⁴⁵ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester Oxford Road Manchester M13 9PL, UK
⁴⁶ European Space Agency/ESRIN Largo Galileo Galilei 1 00044 Frascati Roma, Italy
⁴⁷ Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822 Villeurbanne F-69100, France
⁴⁸ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB) Martí i Franquès 1 08028 Barcelona, Spain
⁴⁹ Institució Catalana de Recerca i Estudis Avançats (ICREA) Passeig de Lluís Companys 23 08010 Barcelona, Spain
⁵⁰ UCB Lyon 1, CNRS/IN2P3, IUF, IP2I Lyon 4 Rue Enrico Fermi 69622 Villeurbanne, France
⁵¹ Mullard Space Science Laboratory, University College London, Holmbury St Mary Dorking Surrey RH5 6NT, UK
⁵² Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8 Campo Grande PT1749-016 Lisboa, Portugal
⁵³ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Campo Grande 1749-016 Lisboa, Portugal
⁵⁴ Department of Astronomy, University of Geneva Ch. d’Ecogia 16 1290 Versoix, Switzerland
⁵⁵ INAF-Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100 00100 Roma, Italy
⁵⁶ INFN-Padova Via Marzolo 8 35131 Padova, Italy
⁵⁷ Aix-Marseille Université, CNRS/IN2P3, CPPM Marseille, France
⁵⁸ Space Science Data Center, Italian Space Agency Via del Politecnico snc 00133 Roma, Italy
⁵⁹ School of Physics, HH Wills Physics Laboratory, University of Bristol Tyndall Avenue Bristol BS8 1TL, UK
⁶⁰ Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München Scheinerstrasse 1 81679 München, Germany
⁶¹ Max Planck Institute for Extraterrestrial Physics Giessenbachstr. 1 85748 Garching, Germany
⁶² Institute of Theoretical Astrophysics, University of Oslo P.O. Box 1029 Blindern 0315 Oslo, Norway
⁶³ Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Drive Pasadena CA 91109, USA
⁶⁴ Department of Physics, Lancaster University Lancaster LA1 4YB, UK
⁶⁵ Felix Hormuth Engineering Goethestr. 17 69181 Leimen, Germany
⁶⁶ Technical University of Denmark Elektrovej 327 2800 Kgs. Lyngby, Denmark
⁶⁷ Cosmic Dawn Center (DAWN)
⁶⁸ Institut d’Astrophysique de Paris, UMR 7095, CNRS, and Sorbonne Université 98 bis Boulevard Arago 75014 Paris, France
⁶⁹ NASA Goddard Space Flight Center Greenbelt MD 20771, USA
⁷⁰ Department of Physics and Helsinki Institute of Physics Gustaf Hällströmin katu 2 00014 University of Helsinki, Finland
⁷¹ Université de Genève, Département de Physique Théorique and Centre for Astroparticle Physics 24 quai Ernest-Ansermet CH-1211 Genève 4, Switzerland
⁷² Department of Physics P.O. Box 64 00014 University of Helsinki, Finland
⁷³ Helsinki Institute of Physics, Gustaf Hällströmin katu 2, University of Helsinki Helsinki, Finland
⁷⁴ Laboratoire d’etude de l’Univers et des phenomenes eXtremes, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS 92190 Meudon, France
⁷⁵ Aix-Marseille Université, CNRS, CNES, LAM Marseille, France
⁷⁶ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield Cheshire SK11 9FT, UK
⁷⁷ Centre de Calcul de l’IN2P3/CNRS 21 Avenue Pierre de Coubertin 69627 Villeurbanne Cedex, France
⁷⁸ Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano Via Celoria 16 20133 Milano, Italy
⁷⁹ INFN-Sezione di Milano Via Celoria 16 20133 Milano, Italy
⁸⁰ University of Applied Sciences and Arts of Northwestern Switzerland, School of Computer Science 5210 Windisch, Switzerland
⁸¹ Universität Bonn, Argelander-Institut für Astronomie Auf dem Hügel 71 53121 Bonn, Germany
⁸² INFN-Sezione di Roma, Piazzale Aldo Moro 2 – c/o Dipartimento di Fisica, Edificio G. Marconi 00185 Roma, Italy
⁸³ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna Via Piero Gobetti 93/2 40129 Bologna, Italy
⁸⁴ Department of Physics, Institute for Computational Cosmology, Durham University South Road Durham DH1 3LE, UK
⁸⁵ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229 06304 Nice Cedex 4, France
⁸⁶ Université Paris Cité, CNRS, Astroparticule et Cosmologie 75013 Paris, France
⁸⁷ CNRS-UCB International Research Laboratory, Centre Pierre Binétruy, IRL2007, CPB-IN2P3 Berkeley, USA
⁸⁸ Institut d’Astrophysique de Paris 98bis Boulevard Arago 75014 Paris, France
⁸⁹ Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny 1290 Versoix, Switzerland
⁹⁰ Aurora Technology for European Space Agency (ESA), Camino bajo del Castillo, s/n Urbanizacion Villafranca del Castillo Villanueva de la Cañada 28692 Madrid, Spain
⁹¹ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB 08193 Bellaterra (Barcelona), Spain
⁹² School of Mathematics and Physics, University of Surrey, Guildford Surrey GU2 7XH, UK
⁹³ DARK, Niels Bohr Institute, University of Copenhagen Jagtvej 155 2200 Copenhagen, Denmark
⁹⁴ Waterloo Centre for Astrophysics, University of Waterloo Waterloo Ontario N2L 3G1, Canada
⁹⁵ Department of Physics and Astronomy, University of Waterloo Waterloo Ontario N2L 3G1, Canada
⁹⁶ Perimeter Institute for Theoretical Physics Waterloo Ontario N2L 2Y5, Canada
⁹⁷ Centre National d’Etudes Spatiales – Centre Spatial de Toulouse 18 Avenue Edouard Belin 31401 Toulouse Cedex 9, France
⁹⁸ Institute of Space Science, Str. Atomistilor Nr. 409 Măgurele Ilfov 077125, Romania
⁹⁹ Consejo Superior de Investigaciones Cientificas Calle Serrano 117 28006 Madrid, Spain
¹⁰⁰ Universidad de La Laguna, Departamento de Astrofísica 38206 La Laguna Tenerife, Spain
¹⁰¹ Caltech/IPAC 1200 E. California Blvd. Pasadena CA 91125, USA
¹⁰² Institut für Theoretische Physik, University of Heidelberg Philosophenweg 16 69120 Heidelberg, Germany
¹⁰³ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, CNRS, UPS, CNES 14 Av. Edouard Belin 31400 Toulouse, France
¹⁰⁴ Université St Joseph; Faculty of Sciences Beirut, Lebanon
¹⁰⁵ Departamento de Física, FCFM, Universidad de Chile, Blanco Encalada 2008 Santiago, Chile
¹⁰⁶ Universität Innsbruck, Institut für Astro- und Teilchenphysik Technikerstr. 25/8 6020 Innsbruck, Austria
¹⁰⁷ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC 08860 Castelldefels Barcelona, Spain
¹⁰⁸ Satlantis, University Science Park Sede Bld 48940 Leioa-Bilbao, Spain
¹⁰⁹ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n 08193 Barcelona, Spain
¹¹⁰ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa Tapada da Ajuda 1349-018 Lisboa, Portugal
¹¹¹ Universidad Politécnica de Cartagena, Departamento de Electrónica y Tecnología de Computadoras Plaza del Hospital 1 30202 Cartagena, Spain
¹¹² INFN-Bologna Via Irnerio 46 40126 Bologna, Italy
¹¹³ Infrared Processing and Analysis Center, California Institute of Technology Pasadena CA 91125, USA
¹¹⁴ INAF, Istituto di Radioastronomia Via Piero Gobetti 101 40129 Bologna, Italy
¹¹⁵ Department of Physics, Oxford University Keble Road Oxford OX1 3RH, UK
¹¹⁶ ICL, Junia, Université Catholique de Lille, LITL 59000 Lille, France

^★★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 9 July 2025
Accepted: 14 November 2025

Abstract

Our comprehension of the history of star formation at z > 3 strongly relies on rest-frame ultraviolet observations. However, this selection systematically misses the dustiest and most massive sources, resulting in an incomplete census at earlier times. Infrared facilities such as Spitzer and the James Webb Space Telescope have shed light on a hidden population lying at z = 3 − 6 characterised by extreme red colours named HIEROs (HST-to-IRAC extremely red objects), identified by the colour criterion H_E − ch2 > 2.25. Recently, Euclid Early Release Observations (EROs) have opened the possibility to further study such objects, exploiting the comparison between Euclid and ancillary Spitzer/IRAC observations. The aim of this study was to investigate the effectiveness of this synergy in characterising the population of a small test area of 232 arcmin². We utilised catalogues in the Perseus field across the VIS and NISP bands, supplemented by data from the four Spitzer channels and several ground-based MegaCam bands (u, g, r, Hα, i, and z) already included in the ERO catalogue. We selected 121 HIEROs by applying the H_E − ch2 > 2.25 colour cut, cleaned this sample of globular clusters and brown dwarfs, and then inspected by eye the multi-band cutouts of each source, ending with 42 reliable HIEROs. Photometric redshifts and other physical properties of the final sample were estimated using the spectral-energy-distribution-fitting software Bagpipes. From the z_phot and M_* values, we computed the galaxy stellar mass function at 3.5 < z < 5.5. When we exclude all galaxies that could host an active galactic nucleus, or whose stellar masses might be overestimated, we still find that the high-mass end of the galaxy stellar mass function is similar to previous estimates, indicating that the true value could be even higher. This investigation highlights the importance of a deeper study of this still mysterious population, in particular to assess its contribution to the cosmic star-formation rate density and its agreement with current galaxy evolution and formation models. These early results demonstrate Euclid’s capabilities to push the boundaries of our understanding of obscured star formation across a wide range of epochs.