Euclid preparation. XXI. Intermediate-redshift contaminants in the search for z >6 galaxies within the Euclid Deep Survey

van Mierlo, S. E.; Caputi, K. I.; Ashby, M.; Atek, H.; Bolzonella, M.; Bowler, R. A. A.; Brammer, G.; Conselice, C. J.; Cuby, J.; Dayal, P.; D??az-S??nchez, A.; Finkelstein, S. L.; Hoekstra, H.; Humphrey, A.; Ilbert, O.; Mccracken, H. J.; Milvang-Jensen, B.; Oesch, P. A.; Pello, R.; Rodighiero, G.; Schirmer, M.; Toft, S.; Weaver, J. R.; Wilkins, S. M.; Willott, C. J.; Zamorani, G.; Amara, A.; Auricchio, N.; Baldi, M.; Bender, R.; Bodendorf, C.; Bonino, D.; Branchini, E.; Brescia, M.; Brinchmann, J.; Camera, S.; Capobianco, V.; Carbone, C.; Carretero, J.; Castellano, M.; Cavuoti, S.; Cimatti, A.; Cledassou, R.; Congedo, G.; Conversi, L.; Copin, Y.; Corcione, L.; Courbin, F.; Da Silva, A.; Degaudenzi, H.; Douspis, M.; Dubath, F.; Dupac, X.; Dusini, S.; Farrens, S.; Ferriol, S.; Frailis, M.; Franceschi, E.; Franzetti, P.; Fumana, M.; Galeotta, S.; Garilli, B.; Gillard, W.; Gillis, B.; Giocoli, C.; Grazian, A.; Grupp, F.; Haugan, S. V. H.; Holmes, W.; Hormuth, F.; Hornstrup, A.; Jahnke, K.; K??mmel, M.; Kiessling, A.; Kilbinger, M.; Kitching, T.; Kohley, R.; Kunz, M.; Kurki-Suonio, H.; Laureijs, R.; Ligori, S.; Lilje, P. B.; Lloro, I.; Maiorano, E.; Mansutti, O.; Marggraf, O.; Markovic, K.; Marulli, F.; Massey, R.; Maurogordato, S.; Medinaceli, E.; Meneghetti, M.; Merlin, E.; Meylan, G.; Moresco, M.; Moscardini, L.; Munari, E.; Niemi, S. M.; Padilla, C.; Paltani, S.; Pasian, F.; Pedersen, K.; Pettorino, V.; Pires, S.; Poncet, M.; Popa, L.; Pozzetti, L.; Raison, F.; Renzi, A.; Rhodes, J.; Riccio, G.; Romelli, E.; Rossetti, E.; Saglia, R.; Sapone, D.; Sartoris, B.; Schneider, P.; Secroun, A.; Sirignano, C.; Sirri, G.; Stanco, L.; Starck, J. -L.; Surace, C.; Tallada-Cresp??, P.; Taylor, A. N.; Tereno, I.; Toledo-Moreo, R.; Torradeflot, F.; Tutusaus, I.; Valentijn, E. A.; Valenziano, L.; Vassallo, T.; Wang, Y.; Zacchei, A.; Zoubian, J.; Andreon, S.; Bardelli, S.; Boucaud, A.; Graci??-Carpio, J.; Maino, D.; Mauri, N.; Mei, S.; Sureau, F.; Zucca, E.; Aussel, H.; Baccigalupi, C.; Balaguera-Antol??nez, A.; Biviano, A.; Blanchard, A.; Borgani, S.; Bozzo, E.; Burigana, C.; Cabanac, R.; Calura, F.; Cappi, A.; Carvalho, C. S.; Casas, S.; Castignani, G.; Colodro-Conde, C.; Cooray, A. R.; Coupon, J.; Courtois, H. M.; Crocce, M.; Cucciati, O.; Davini, S.; Dole, H.; Escartin, J. A.; Escoffier, S.; Fabricius, M.; Farina, M.; Ganga, K.; Garc??a-Bellido, J.; George, K.; Giacomini, F.; Gozaliasl, G.; Gwyn, S.; Hook, I.; Huertas-Company, M.; Kansal, V.; Kashlinsky, A.; Keihanen, E.; Kirkpatrick, C. C.; Lindholm, V.; Maoli, R.; Martinelli, M.; Martinet, N.; Maturi, M.; Metcalf, R. B.; Monaco, P.; Morgante, G.; Nucita, A. A.; Patrizii, L.; Peel, A.; Pollack, J.; Popa, V.; Porciani, C.; Potter, D.; Reimberg, P.; S??nchez, A. G.; Scottez, V.; Sefusatti, E.; Stadel, J.; Teyssier, R.; Valiviita, J.; Viel, M.

doi:10.1051/0004-6361/202243950

Context. The Euclid mission is expected to discover thousands of z > 6 galaxies in three deep fields, which together will cover a similar to 50 deg(2) area. However, the limited number of Euclid bands (four) and the low availability of ancillary data could make the identification of z > 6 galaxies challenging.Aims. In this work we assess the degree of contamination by intermediate-redshift galaxies (z = 1-5.8) expected for z > 6 galaxies within the Euclid Deep Survey.Methods. This study is based on similar to 176 000 real galaxies at z = 1-8 in a similar to 0.7 deg(2) area selected from the UltraVISTA ultra-deep survey and similar to 96 000 mock galaxies with 25.3 <= H < 27.0, which altogether cover the range of magnitudes to be probed in the Euclid Deep Survey. We simulate Euclid and ancillary photometry from fiducial 28-band photometry and fit spectral energy distributions to various combinations of these simulated data.Results. We demonstrate that identifying z > 6 galaxies with Euclid data alone will be very effective, with a z > 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 > 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 minimised to 7% when including ultra-deep Rubin data. For UltraVISTA-like bright galaxies, we find that Euclid (I-E - Y-E) > 2:8 and (Y-E - J(E)) < 1.4 colour criteria can separate contaminants from true z > 6 galaxies, although these are applicable to only 54% of the contaminants as many have unconstrained (I-E - Y-E) colours. In the best scenario, these cuts reduce the contamination fraction to 1% whilst preserving 81% of the fiducial z > 6 sample. For the faint mock sample, colour cuts are infeasible; we find instead that a 5 sigma detection threshold requirement in at least one of the Euclid near-infrared bands reduces the contamination fraction to 25%.

Euclid preparation. XXI. Intermediate-redshift contaminants in the search for z >6 galaxies within the Euclid Deep Survey / S. E. van Mierlo; K. I. Caputi; M. Ashby; H. Atek; M. Bolzonella; R. A. A. Bowler; G. Brammer; C. J. Conselice; J. Cuby; P. Dayal; A. D??az-S??nchez; S. L. Finkelstein; H. Hoekstra; A. Humphrey; O. Ilbert; H. J. McCracken; B. Milvang-Jensen; P. A. Oesch; R. Pello; G. Rodighiero; M. Schirmer; S. Toft; J. R. Weaver; S. M. Wilkins; C. J. Willott; G. Zamorani; A. Amara; N. Auricchio; M. Baldi; R. Bender; C. Bodendorf; D. Bonino; E. Branchini; M. Brescia; J. Brinchmann; S. Camera; V. Capobianco; C. Carbone; J. Carretero; M. Castellano; S. Cavuoti; A. Cimatti; R. Cledassou; G. Congedo; L. Conversi; Y. Copin; L. Corcione; F. Courbin; A. Da Silva; H. Degaudenzi; M. Douspis; F. Dubath; X. Dupac; S. Dusini; S. Farrens; S. Ferriol; M. Frailis; E. Franceschi; P. Franzetti; M. Fumana; S. Galeotta; B. Garilli; W. Gillard; B. Gillis; C. Giocoli; A. Grazian; F. Grupp; S. V. H. Haugan; W. Holmes; F. Hormuth; A. Hornstrup; K. Jahnke; M. K??mmel; A. Kiessling; M. Kilbinger; T. Kitching; R. Kohley; M. Kunz; H. Kurki-Suonio; R. Laureijs; S. Ligori; P. B. Lilje; I. Lloro; E. Maiorano; O. Mansutti; O. Marggraf; K. Markovic; F. Marulli; R. Massey; S. Maurogordato; E. Medinaceli; M. Meneghetti; E. Merlin; G. Meylan; M. Moresco; L. Moscardini; E. Munari; S. M. Niemi; C. Padilla; S. Paltani; F. Pasian; K. Pedersen; V. Pettorino; S. Pires; M. Poncet; L. Popa; L. Pozzetti; F. Raison; A. Renzi; J. Rhodes; G. Riccio; E. Romelli; E. Rossetti; R. Saglia; D. Sapone; B. Sartoris; P. Schneider; A. Secroun; C. Sirignano; G. Sirri; L. Stanco; J.-L. Starck; C. Surace; P. Tallada-Cresp??; A. N. Taylor; I. Tereno; R. Toledo-Moreo; F. Torradeflot; I. Tutusaus; E. A. Valentijn; L. Valenziano; T. Vassallo; Y. Wang; A. Zacchei; J. Zoubian; S. Andreon; S. Bardelli; A. Boucaud; J. Graci??-Carpio; D. Maino; N. Mauri; S. Mei; F. Sureau; E. Zucca; H. Aussel; C. Baccigalupi; A. Balaguera-Antol??nez; A. Biviano; A. Blanchard; S. Borgani; E. Bozzo; C. Burigana; R. Cabanac; F. Calura; A. Cappi; C. S. Carvalho; S. Casas; G. Castignani; C. Colodro-Conde; A. R. Cooray; J. Coupon; H. M. Courtois; M. Crocce; O. Cucciati; S. Davini; H. Dole; J. A. Escartin; S. Escoffier; M. Fabricius; M. Farina; K. Ganga; J. Garc??a-Bellido; K. George; F. Giacomini; G. Gozaliasl; S. Gwyn; I. Hook; M. Huertas-Company; V. Kansal; A. Kashlinsky; E. Keihanen; C. C. Kirkpatrick; V. Lindholm; R. Maoli; M. Martinelli; N. Martinet; M. Maturi; R. B. Metcalf; P. Monaco; G. Morgante; A. A. Nucita; L. Patrizii; A. Peel; J. Pollack; V. Popa; C. Porciani; D. Potter; P. Reimberg; A. G. S??nchez; V. Scottez; E. Sefusatti; J. Stadel; R. Teyssier; J. Valiviita; M. Viel. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - STAMPA. - 666:(2022), pp. A200.1-A200.27. [10.1051/0004-6361/202243950]