Euclid preparation

I. The Euclid Wide Survey

¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
e-mail: roberto.scaramella@inaf.it
² INFN – Sezione di Roma, Piazzale Aldo Moro, 2 c/o Dipartimento di Fisica, Edificio G. Marconi, 00185 Roma, Italy
³ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
⁴ CEA Saclay, DFR/IRFU, Service d’Astrophysique, Bât. 709, 91191 Gif-sur-Yvette, France
⁵ Institut d’Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France
⁶ INFN – Bologna, Via Irnerio 46, 40126 Bologna, Italy
⁷ Dipartimento di Fisica e Scienze della Terra, Universitá degli Studi di Ferrara, Via Giuseppe Saragat 1, 44122 Ferrara, Italy
⁸ INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, 40129 Bologna, Italy
⁹ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
¹⁰ Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016 Lisboa, Portugal
¹¹ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
¹² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
¹³ IFPU, Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151 Trieste, Italy
¹⁴ INAF – Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy
¹⁵ European Space Agency/ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁶ ESAC/ESA, Camino Bajo del Castillo, s/n, Urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁷ FRACTAL S.L.N.E., Calle Tulipán 2, Portal 13 1A, 28231 Las Rozas de Madrid, Spain
¹⁸ European Space Agency/ESOC, Robert-Bosch-Str. 5, 64293 Darmstadt, Germany
¹⁹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁰ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
²¹ Univ. Lyon, Univ. Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822, 69622 Villeurbanne, France
²² INAF – IASF Milano, Via Alfonso Corti 12, 20133 Milano, Italy
²³ Aix-Marseille Univ., CNRS/IN2P3, CPPM, Marseille, France
²⁴ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20122 Milano, Italy
²⁵ Dipartimento di Fisica “Aldo Pontremoli”, Universitá degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
²⁶ INFN – Sezione di Milano, Via Celoria 16, 20133 Milano, Italy
²⁷ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
²⁸ Aix-Marseille Univ., CNRS, CNES, LAM, Marseille, France
²⁹ INFN – Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
³⁰ Department of Physics, Oxford University, Keble Road, Oxford OX1 3RH, UK
³¹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
³² Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada
³³ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
³⁴ Centre for Astrophysics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
³⁵ Carnegie Observatories, Pasadena, CA 91101, USA
³⁶ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
³⁷ Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX, UK
³⁸ INAF – Osservatorio Astronomico di Padova, Via dell’Osservatorio 5, 35122 Padova, Italy
³⁹ Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstrasse 1, 81679 München, Germany
⁴⁰ Max Planck Institute for Extraterrestrial Physics, Giessenbachstr. 1, 85748 Garching, Germany
⁴¹ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, TO, Italy
⁴² INFN – Sezione di Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy
⁴³ Department of Mathematics and Physics, Roma Tre University, Via della Vasca Navale 84, 00146 Rome, Italy
⁴⁴ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, CNRS, UPS, CNES, 14 Av. Edouard Belin, 31400 Toulouse, France
⁴⁵ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
⁴⁶ Department of Astronomy & Astrophysics, University of Toronto, 50 St George Street, Toronto, Ontario M5S 3H4, Canada
⁴⁷ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra, Barcelona, Spain
⁴⁸ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
⁴⁹ Institut d’Estudis Espacials de Catalunya (IEEC), Carrer Gran Capitá 2-4, 08034 Barcelona, Spain
⁵⁰ Department of Physics “E. Pancini”, University Federico II, Via Cinthia 6, 80126 Napoli, Italy
⁵¹ INFN Section of Naples, Via Cinthia 6, 80126 Napoli, Italy
⁵² Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Universitá di Bologna, Via Piero Gobetti 93/2, 40129 Bologna, Italy
⁵³ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁵⁴ Institut National de Physique Nucléaire et de Physique des Particules, 3 Rue Michel-Ange, 75794 Paris Cedex 16, France
⁵⁵ Centre National d’Etudes Spatiales, Toulouse, France
⁵⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁵⁷ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁵⁸ European Space Agency/ESRIN, Largo Galileo Galilei 1, 00044 Frascati, Roma, Italy
⁵⁹ Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
⁶⁰ Department of Astronomy, University of Geneva, ch. dÉcogia 16, 1290 Versoix, Switzerland
⁶¹ INFN – Padova, Via Marzolo 8, 35131 Padova, Italy
⁶² Istituto Nazionale di Astrofisica (INAF) – Osservatorio di Astrofisica e Scienza dello Spazio (OAS), Via Gobetti 93/3, 40127 Bologna, Italy
⁶³ Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Via Irnerio 46, 40126 Bologna, Italy
⁶⁴ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
⁶⁵ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁶⁶ von Hoerner & Sulger GmbH, SchloßPlatz 8, 68723 Schwetzingen, Germany
⁶⁷ University of Lyon, UCB Lyon 1, CNRS/IN2P3, IUF, IP2I Lyon, France
⁶⁸ Université de Genève, Département de Physique Théorique and Centre for Astroparticle Physics, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland
⁶⁹ Department of Physics and Helsinki Institute of Physics, University of Helsinki, Gustaf Hällströmin katu 2, 00014 Helsinki, Finland
⁷⁰ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁷¹ NOVA Optical Infrared Instrumentation Group at ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁷² Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁷³ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁷⁴ University of Applied Sciences and Arts of Northwestern Switzerland, School of Engineering, 5210 Windisch, Switzerland
⁷⁵ Observatoire de Sauverny, Ecole Polytechnique Fédérale de Lausanne, 1290 Versoix, Switzerland
⁷⁶ Department of Physics and Astronomy, University of Aarhus, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁷⁷ Institute of Space Science, Bucharest 077125, Romania
⁷⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁷⁹ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38204 San Cristóbal de La Laguna, Tenerife, Spain
⁸⁰ Dipartimento di Fisica e Astronomia “G.Galilei”, Universitá di Padova, Via Marzolo 8, 35131 Padova, Italy
⁸¹ Centre for Electronic Imaging, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁸² Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Avenida Complutense 40, 28040 Madrid, Spain
⁸³ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
⁸⁴ Universidad Politécnica de Cartagena, Departamento de Electrónica y Tecnología de Computadoras, 30202 Cartagena, Spain
⁸⁵ INAF – IASF Bologna, Via Piero Gobetti 101, 40129 Bologna, Italy
⁸⁶ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
⁸⁷ Université de Paris, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
⁸⁸ INFN – Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁸⁹ Dipartimento di Fisica, Universitá degli Studi di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁹⁰ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
⁹¹ Department of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
⁹² Space Science Data Center, Italian Space Agency, Via del Politecnico snc, 00133 Roma, Italy
⁹³ SISSA, International School for Advanced Studies, Via Bonomea 265, 34136 Trieste, TS, Italy
⁹⁴ INFN, Sezione di Trieste, Via Valerio 2, 34127 Trieste, TS, Italy
⁹⁵ Dipartimento di Fisica – Sezione di Astronomia, Universitá di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
⁹⁶ Dept. of Physics, IIT Hyderabad, Kandi, Telangana 502285, India
⁹⁷ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, 00100 Roma, Italy
⁹⁸ School of Physics, HH Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
⁹⁹ Research Program in Systems Oncology, Faculty of Medicine, University of Helsinki, Helsinki, Finland
¹⁰⁰ Department of Physics, University of Helsinki, PO Box 64 00014 Helsinki, Finland
¹⁰¹ Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
¹⁰² Helsinki Institute of Physics, University of Helsinki, Gustaf Hällströmin katu 2, Helsinki, Finland
¹⁰³ Centre de Calcul de l’IN2P3, 21 Avenue Pierre de Coubertin, 69627 Villeurbanne Cedex, France
¹⁰⁴ Instituto de Física Teórica UAM-CSIC, Campus de Cantoblanco, 28049 Madrid, Spain
¹⁰⁵ Institut für Theoretische Physik, University of Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany
¹⁰⁶ Zentrum für Astronomie, Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany
¹⁰⁷ Sorbonne Universités, UPMC Univ. Paris 6 et CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
¹⁰⁸ ICC&CEA, Department of Physics, Durham University, South Road DH1 3LE, UK
¹⁰⁹ INFN, Sezione di Lecce, Via per Arnesano, CP-193, 73100 Lecce, Italy
¹¹⁰ Department of Mathematics and Physics E. De Giorgi, University of Salento, Via per Arnesano, CP-I93, 73100 Lecce, Italy
¹¹¹ Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
¹¹² Departamento de Física, FCFM, Universidad de Chile, Blanco Encalada 2008, Santiago, Chile
¹¹³ Department of Physics, University of Jyväskylä, PO Box 35 (YFL) 40014 Jyväskylä, Finland

Received: 2 August 2021
Accepted: 22 October 2021

Abstract

Euclid is a mission of the European Space Agency that is designed to constrain the properties of dark energy and gravity via weak gravitational lensing and galaxy clustering. It will carry out a wide area imaging and spectroscopy survey (the Euclid Wide Survey: EWS) in visible and near-infrared bands, covering approximately 15 000 deg² of extragalactic sky in six years. The wide-field telescope and instruments are optimised for pristine point spread function and reduced stray light, producing very crisp images. This paper presents the building of the Euclid reference survey: the sequence of pointings of EWS, deep fields, and calibration fields, as well as spacecraft movements followed by Euclid as it operates in a step-and-stare mode from its orbit around the Lagrange point L2. Each EWS pointing has four dithered frames; we simulated the dither pattern at the pixel level to analyse the effective coverage. We used up-to-date models for the sky background to define the Euclid region-of-interest (RoI). The building of the reference survey is highly constrained from calibration cadences, spacecraft constraints, and background levels; synergies with ground-based coverage were also considered. Via purposely built software, we first generated a schedule for the calibrations and deep fields observations. On a second stage, the RoI was tiled and scheduled with EWS observations, using an algorithm optimised to prioritise the best sky areas, produce a compact coverage, and ensure thermal stability. The result is the optimised reference survey RSD_2021A, which fulfils all constraints and is a good proxy for the final solution. The current EWS covers ≈14 500 deg². The limiting AB magnitudes (5σ point-like source) achieved in its footprint are estimated to be 26.2 (visible band I_E) and 24.5 (for near infrared bands Y_E, J_E, H_E); for spectroscopy, the Hα line flux limit is 2 × 10⁻¹⁶ erg⁻¹ cm⁻² s⁻¹ at 1600 nm; and for diffuse emission, the surface brightness limits are 29.8 (visible band) and 28.4 (near infrared bands) mag arcsec⁻².