Euclid preparation. XXI. Intermediate-redshift contaminants in the search for $z&gt;6$ galaxies within the Euclid Deep Survey
Creators: name: Euclid Collaboration
name: van Mierlo, S. E.
name: Caputi, K. I.
name: Ashby, M.
name: Atek, H.
name: Bolzonella, M.
name: Bowler, R. A. A.
name: Brammer, G.
name: Conselice, C. J.
name: Cuby, J.
name: Dayal, P.
name: Díaz-Sánchez, A.
name: Finkelstein, S. L.
name: Hoekstra, H.
name: Humphrey, A.
name: Ilbert, O.
name: McCracken, H. J.
name: Milvang-Jensen, B.
name: Oesch, P. A.
name: Pello, R.
name: Rodighiero, G.
name: Schirmer, M.
name: Toft, S.
name: Weaver, J. R.
name: Wilkins, S. M.
name: Willott, C. J.
name: Zamorani, G.
name: Amara, A.
name: Auricchio, N.
name: Baldi, M.
name: Bender, R.
name: Bodendorf, C.
name: Bonino, D.
name: Branchini, E.
name: Brescia, M.
name: Brinchmann, J.
name: Camera, S.
name: Capobianco, V.
name: Carbone, C.
name: Carretero, J.
name: Castellano, M.
name: Cavuoti, S.
name: Cimatti, A.
name: Cledassou, R.
name: Congedo, G.
name: Conversi, L.
name: Copin, Y.
name: Corcione, L.
name: Courbin, F.
name: Da Silva, A.
name: Degaudenzi, H.
name: Douspis, M.
name: Dubath, F.
name: Dupac, X.
name: Dusini, S.
name: Farrens, S.
name: Ferriol, S.
name: Frailis, M.
name: Franceschi, E.
name: Franzetti, P.
name: Fumana, M.
name: Galeotta, S.
name: Garilli, B.
name: Gillard, W.
name: Gillis, B.
name: Giocoli, C.
name: Grazian, A.
name: Grupp, F.
name: Haugan, S. V. H.
name: Holmes, W.
name: Hormuth, F.
name: Hornstrup, A.
name: Jahnke, K.
name: Kümmel, M.
name: Kiessling, A.
name: Kilbinger, M.
name: Kitching, T.
name: Kohley, R.
name: Kunz, M.
name: Kurki-Suonio, H.
name: Laureijs, R.
name: Ligori, S.
name: Lilje, P. B.
name: Lloro, I.
name: Maiorano, E.
name: Mansutti, O.
name: Marggraf, O.
name: Markovic, K.
name: Marulli, F.
name: Massey, R.
name: Maurogordato, S.
name: Medinaceli, E.
name: Meneghetti, M.
name: Merlin, E.
name: Meylan, G.
name: Moresco, M.
name: Moscardini, L.
name: Munari, E.
name: Niemi, S. M.
name: Padilla, C.
name: Paltani, S.
name: Pasian, F.
name: Pedersen, K.
name: Pettorino, V.
name: Pires, S.
name: Poncet, M.
name: Popa, L.
name: Pozzetti, L.
name: Raison, F.
name: Renzi, A.
name: Rhodes, J.
name: Riccio, G.
name: Romelli, E.
name: Rossetti, E.
name: Saglia, R.
name: Sapone, D.
name: Sartoris, B.
name: Schneider, P.
name: Secroun, A.
name: Sirignano, C.
name: Sirri, G.
name: Stanco, L.
name: Starck, J. -L.
name: Surace, C.
name: Tallada-Crespí, P.
name: Taylor, A. N.
name: Tereno, I.
name: Toledo-Moreo, R.
name: Torradeflot, F.
name: Tutusaus, I.
name: Valentijn, E. A.
name: Valenziano, L.
name: Vassallo, T.
name: Wang, Y.
name: Zacchei, A.
name: Zoubian, J.
name: Andreon, S.
name: Bardelli, S.
name: Boucaud, A.
name: Graciá-Carpio, J.
name: Maino, D.
name: Mauri, N.
name: Mei, S.
name: Sureau, F.
name: Zucca, E.
name: Aussel, H.
name: Baccigalupi, C.
name: Balaguera-Antolínez, A.
name: Biviano, A.
name: Blanchard, A.
name: Borgani, S.
name: Bozzo, E.
name: Burigana, C.
name: Cabanac, R.
name: Calura, F.
name: Cappi, A.
name: Carvalho, C. S.
name: Casas, S.
name: Castignani, G.
name: Colodro-Conde, C.
name: Cooray, A. R.
name: Coupon, J.
name: Courtois, H. M.
name: Crocce, M.
name: Cucciati, O.
name: Davini, S.
name: Dole, H.
name: Escartin, J. A.
name: Escoffier, S.
name: Fabricius, M.
name: Farina, M.
name: Ganga, K.
name: García-Bellido, J.
name: George, K.
name: Giacomini, F.
name: Gozaliasl, G.
name: Gwyn, S.
name: Hook, I.
name: Huertas-Company, M.
name: Kansal, V.
name: Kashlinsky, A.
name: Keihanen, E.
name: Kirkpatrick, C. C.
name: Lindholm, V.
name: Maoli, R.
name: Martinelli, M.
name: Martinet, N.
name: Maturi, M.
name: Metcalf, R. B.
name: Monaco, P.
name: Morgante, G.
name: Nucita, A. A.
name: Patrizii, L.
name: Peel, A.
name: Pollack, J.
name: Popa, V.
name: Porciani, C.
name: Potter, D.
name: Reimberg, P.
name: Sánchez, A. G.
name: Scottez, V.
name: Sefusatti, E.
name: Stadel, J.
name: Teyssier, R.
name: Valiviita, J.
name: Viel, M.
Publisher: name: arXiv
Year: 2022
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: (Abridged) The Euclid mission is expected to discover thousands of z&gt;6 galaxies in three Deep Fields, which together will cover a ~40 deg2 area. However, the limited number of Euclid bands and availability of ancillary data could make the identification of z&gt;6 galaxies challenging. In this work, we assess the degree of contamination by intermediate-redshift galaxies (z=1-5.8) expected for z&gt;6 galaxies within the Euclid Deep Survey. This study is based on ~176,000 real galaxies at z=1-8 in a ~0.7 deg2 area selected from the UltraVISTA ultra-deep survey, and ~96,000 mock galaxies with 25.3$\leq$H&lt;27.0, which altogether cover the range of magnitudes to be probed in the Euclid Deep Survey. We simulate Euclid and ancillary photometry from the fiducial, 28-band photometry, and fit spectral energy distributions (SEDs) to various combinations of these simulated data. Our study demonstrates that identifying z&gt;6 with Euclid data alone will be very effective, with a z&gt;6 recovery of 91(88)% for bright (faint) galaxies. For the UltraVISTA-like bright sample, the percentage of z=1-5.8 contaminants amongst apparent z&gt;6 galaxies as observed with Euclid alone is 18%, which is reduced to 4(13)% by including ultra-deep Rubin (Spitzer) photometry. Conversely, for the faint mock sample, the contamination fraction with Euclid alone is considerably higher at 39%, and minimized to 7% when including ultra-deep Rubin data. For UltraVISTA-like bright galaxies, we find that Euclid (I-Y)&gt;2.8 and (Y-J)&lt;1.4 colour criteria can separate contaminants from true z&gt;6 galaxies, although these are applicable to only 54% of the contaminants, as many have unconstrained (I-Y) colours. In the most optimistic scenario, these cuts reduce the contamination fraction to 1% whilst preserving 81% of the fiducial z&gt;6 sample. For the faint mock sample, colour cuts are infeasible.
description: 27 pages, 14 figures, 9 tables; version accepted for publication by A&amp;A