Euclid Collaboration, R. Scaramella, J. Amiaux, Y. Mellier, C. Burigana, C. S. Carvalho, J.-C. Cuillandre, A. C. da Silva, A. Derosa, J. Dinis, E. Maiorano, M. Maris, I. Tereno, R. J. Laureijs, T. Boenke, G. Buenadicha, X. Dupac, L. Gaspar Venancio, P. Gómez-Álvarez, J. Hoar, J. Lorenzo Alvarez, G. D. Racca, G. Saavedra-Criado, J. Schwartz, R. Vavrek, M. Schirmer, H. Aussel, R. Azzollini, V. F. Cardone, M. Cropper, A. Ealet, B. Garilli, W. Gillard, B. R. Granett, L. Guzzo, H. Hoekstra, K. Jahnke, T. D. Kitching, T. Maciaszek, M. Meneghetti, L. Miller, R. Nakajima, S. M. Niemi, F. Pasian, W. J. Percival, S. Pottinger, M. Sauvage, M. Scodeggio, S. Wachter, A. Zacchei, N. Aghanim, A. Amara, T. Auphan, N. Auricchio, S. Awan, A. Balestra, R. Bender, C. Bodendorf, D. Bonino, E. Branchini, S. Brau-Nogue, M. Brescia, G. P. Candini, V. Capobianco, C. Carbone, R. G. Carlberg, J. Carretero, R. Casas, F. J. Castander, M. Castellano, S. Cavuoti, A. Cimatti, R. Cledassou, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, L. Corcione, A. Costille, F. Courbin, H. Degaudenzi, M. Douspis, F. Dubath, C. A. J. Duncan, S. Dusini, S. Farrens, S. Ferriol, P. Fosalba, N. Fourmanoit, M. Frailis, E. Franceschi, P. Franzetti, M. Fumana, B. R. Gillis, C. Giocoli, A. Grazian, F. Grupp, S. V. H. Haugan, W. A. Holmes, F. Hormuth, P. Hudelot, S. Kermiche, A. Kiessling, M. Kilbinger, R. Kohley, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, O. Lahav, S. Ligori, P. B. Lilje, I. Lloro, O. Mansutti, O. Marggraf, K. Markovic, F. Marulli, R. Massey, S. Maurogordato, M. Melchior, E. Merlin, G. Meylan, J. J. Mohr, M. Moresco, B. Morin, L. Moscardini, E. Munari, R. C. Nichol, C. Padilla, S. Paltani, J. Peacock, K. Pedersen, V. Pettorino, S. Pires, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, R. Rebolo López, J. D. Rhodes, H. -W. Rix, M. Roncarelli, E. Rossetti, R. Saglia, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, S. Serrano, C. Sirignano, G. Sirri, J. Skottfelt, L. Stanco, J.-L. Starck, P. Tallada-Crespí, D. Tavagnacco, A. N. Taylor, H. I. Teplitz, R. Toledo-Moreo, F. Torradeflot, M. Trifoglio, E. A. Valentijn, L. Valenziano, G. A. Verdoes Kleijn, Y. Wang, N. Welikala, J. Weller, M. Wetzstein, G. Zamorani, J. Zoubian, S. Andreon, M. Baldi, S. Bardelli, A. Boucaud, S. Camera, D. Di Ferdinando, G. Fabbian, R. Farinelli, S. Galeotta, J. Graciá-Carpio, D. Maino, E. Medinaceli, S. Mei, C. Neissner, G. Polenta, A. Renzi, E. Romelli, C. Rosset, F. Sureau, M. Tenti, T. Vassallo, E. Zucca, C. Baccigalupi, A. Balaguera-Antolínez, P. Battaglia, A. Biviano, S. Borgani, E. Bozzo, R. Cabanac, A. Cappi, S. Casas, G. Castignani, C. Colodro-Conde, J. Coupon, H. M. Courtois, J.-G. Cuby, S. de la Torre, S. Desai, H. Dole, M. Fabricius, M. Farina, P. G. Ferreira, F. Finelli, P. Flose-Reimberg, S. Fotopoulou, K. Ganga, G. Gozaliasl, I. M. Hook, E. Keihanen, C. C. Kirkpatrick, P. Liebing, V. Lindholm, G. Mainetti, M. Martinelli, N. Martinet, M. Maturi, H. J. McCracken, R. B. Metcalf, G. Morgante, J. W. Nightingale, A. A. Nucita, L. Patrizii, D. Potter, G. Riccio, A. G. Sánchez, D. Sapone, J. A. Schewtschenko, M. Schultheis, V. Scottez, R. Teyssier, I. Tutusaus, J. Valiviita, M. Viel, W. Vriend, L. Whittaker

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 IE) 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.

Keywords
space vehicles / surveys / methods: numerical / dark energy / dark matter

Astronomy & Astrophysics
Volume 662, Article Number A112, Number of pages 41
2022 June

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