Euclid preparation I. The Euclid Wide Survey

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

doi:10.1051/0004-6361/202141938

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 deg(2) 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 approximate to 14 & x2006;500 deg(2). The limiting AB magnitudes (5 sigma 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 H alpha line flux limit is 2 x 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).