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

Creators: Euclid Collaboration; van Mierlo, S. E.¹; Caputi, K. I.^{1, 2}; Ashby, M.³; Atek, H.⁴; Bolzonella, M.⁵; Bowler, R. A. A.^{6, 7}; Brammer, G.²; Conselice, C. J.⁶; Cuby, J.⁸; Dayal, P.¹; Díaz-Sánchez, A.⁹; Finkelstein, S. L.¹⁰; Hoekstra, H.¹¹; Humphrey, A.¹²; Ilbert, O.⁸; McCracken, H. J.^{4, 13}; Milvang-Jensen, B.²; Oesch, P. A.^{2, 14}; Pello, R.⁸; Rodighiero, G.¹⁵; Schirmer, M.¹⁶; Toft, S.²; Weaver, J. R.²; Wilkins, S. M.¹⁷; Willott, C. J.¹⁸; Zamorani, G.⁵; Amara, A.¹⁹; Auricchio, N.⁵; Baldi, M.^{20, 5, 21}; Bender, R.^{22, 23}; Bodendorf, C.²²; Bonino, D.²⁴; Branchini, E.^{25, 26}; Brescia, M.²⁷; Brinchmann, J.¹²; Camera, S.^{28, 29, 24}; Capobianco, V.²⁴; Carbone, C.³⁰; Carretero, J.³¹; Castellano, M.³²; Cavuoti, S.^{27, 33, 34}; Cimatti, A.^{20, 35}; Cledassou, R.^{36, 37}; Congedo, G.³⁸; Conversi, L.^{39, 40}; Copin, Y.⁴¹; Corcione, L.²⁴; Courbin, F.⁴²; Da Silva, A.⁴³; Degaudenzi, H.¹⁴; Douspis, M.⁴⁴; Dubath, F.¹⁴; Dupac, X.⁴⁰; Dusini, S.⁴⁵; Farrens, S.⁴⁶; Ferriol, S.⁴¹; Frailis, M.⁴⁷; Franceschi, E.⁵; Franzetti, P.³⁰; Fumana, M.³⁰; Galeotta, S.⁴⁷; Garilli, B.³⁰; Gillard, W.⁴⁸; Gillis, B.³⁸; Giocoli, C.^{49, 21}; Grazian, A.⁵⁰; Grupp, F.^{22, 23}; Haugan, S. V. H.⁵¹; Holmes, W.⁵²; Hormuth, F.; Hornstrup, A.⁵³; Jahnke, K.¹⁶; Kümmel, M.²³; Kiessling, A.⁵²; Kilbinger, M.⁵⁴; Kitching, T.⁵⁵; Kohley, R.⁴⁰; Kunz, M.¹⁴; Kurki-Suonio, H.⁵⁶; Laureijs, R.⁵⁷; Ligori, S.²⁴; Lilje, P. B.⁵¹; Lloro, I.⁵⁸; Maiorano, E.⁵; Mansutti, O.⁴⁷; Marggraf, O.⁵⁹; Markovic, K.⁵²; Marulli, F.^{20, 5, 21}; Massey, R.⁶⁰; Maurogordato, S.⁶¹; Medinaceli, E.⁴⁹; Meneghetti, M.^{5, 21}; Merlin, E.³²; Meylan, G.⁴²; Moresco, M.^{20, 5}; Moscardini, L.^{20, 5, 21}; Munari, E.⁴⁷; Niemi, S. M.⁵⁷; Padilla, C.³¹; Paltani, S.¹⁴; Pasian, F.⁴⁷; Pedersen, K.⁶²; Pettorino, V.⁵⁴; Pires, S.⁴⁶; Poncet, M.³⁶; Popa, L.⁶³; Pozzetti, L.⁵; Raison, F.²²; Renzi, A.^{15, 45}; Rhodes, J.⁵²; Riccio, G.²⁷; Romelli, E.⁴⁷; Rossetti, E.²⁰; Saglia, R.^{22, 23}; Sapone, D.⁶⁴; Sartoris, B.^{65, 47}; Schneider, P.⁵⁹; Secroun, A.⁴⁸; Sirignano, C.^{15, 45}; Sirri, G.²¹; Stanco, L.⁴⁵; Starck, J.-L.⁴⁶; Surace, C.⁸; Tallada-Crespí, P.⁶⁶; Taylor, A. N.³⁸; Tereno, I.⁴³; Toledo-Moreo, R.⁹; Torradeflot, F.⁶⁶; Tutusaus, I.¹⁴; Valentijn, E. A.¹; Valenziano, L.^{5, 21}; Vassallo, T.²³; Wang, Y.^{67, 68}; Zacchei, A.⁴⁷; Zoubian, J.⁴⁸; Andreon, S.⁶⁹; Bardelli, S.⁵; Boucaud, A.⁷⁰; Graciá-Carpio, J.²²; Maino, D.^{71, 30, 72}; Mauri, N.^{20, 21}; Mei, S.⁷⁰; Sureau, F.⁴⁶; Zucca, E.⁵; Aussel, H.⁴⁶; Baccigalupi, C.^{65, 47, 73, 74}; Balaguera-Antolínez, A.^{75, 76}; Biviano, A.^{47, 65}; Blanchard, A.⁷⁷; Borgani, S.^{47, 65, 73, 78}; Bozzo, E.¹⁴; Burigana, C.^{79, 49, 21}; Cabanac, R.⁷⁷; Calura, F.⁵; Cappi, A.^{61, 5}; Carvalho, C. S.⁴³; Casas, S.⁸⁰; Castignani, G.^{20, 5}; Colodro-Conde, C.⁷⁵; Cooray, A. R.⁸¹; Coupon, J.¹⁴; Courtois, H. M.⁴¹; Crocce, M.⁸²; Cucciati, O.⁵; Davini, S.⁸³; Dole, H.⁴⁴; Escartin, J. A.²²; Escoffier, S.⁴⁸; Fabricius, M.²²; Farina, M.⁸⁴; Ganga, K.⁷⁰; García-Bellido, J.⁸⁵; George, K.²³; Giacomini, F.²¹; Gozaliasl, G.⁵⁶; Gwyn, S.¹⁸; Hook, I.⁸⁶; Huertas-Company, M.^{54, 87, 75}; Kansal, V.⁴⁶; Kashlinsky, A.^{88, 89}; Keihanen, E.⁵⁶; Kirkpatrick, C. C.⁵⁶; Lindholm, V.⁵⁶; Maoli, R.^{90, 32}; Martinelli, M.³²; Martinet, N.⁸; Maturi, M.⁹¹; Metcalf, R. B.^{20, 5}; Monaco, P.^{78, 65, 47, 73}; Morgante, G.⁵; Nucita, A. A.^{92, 93, 94}; Patrizii, L.²¹; Peel, A.⁴²; Pollack, J.⁷⁰; Popa, V.⁶³; Porciani, C.⁵⁹; Potter, D.⁹⁵; Reimberg, P.⁴; Sánchez, A. G.²²; Scottez, V.⁴; Sefusatti, E.^{47, 65, 73}; Stadel, J.⁹⁵; Teyssier, R.⁹⁶; Valiviita, J.^{97, 98}; Viel, M.^{47, 65, 74, 73}

1. University of Groningen
2. University of Copenhagen
3. Harvard-Smithsonian Center for Astrophysics
4. Institut d'Astrophysique de Paris
5. INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129, Bologna, Italy
6. University of Manchester
7. University of Oxford
8. Aix-Marseille Univ, CNRS, CNES, LAM, Marseille, France
9. Polytechnic University of Cartagena
10. The University of Texas at Austin
11. Leiden University
12. University of Porto
13. Sorbonne University
14. University of Geneva
15. University of Padua
16. Max Planck Institute for Astronomy
17. University of Sussex
18. NRC Herzberg, 5071 West Saanich Rd, Victoria, BC, V9E 2E7, Canada
19. University of Portsmouth
20. University of Bologna
21. INFN Sezione di Bologna
22. Max Planck Institute for Extraterrestrial Physics
23. Ludwig-Maximilians-Universität München
24. Osservatorio Astrofisico di Torino
25. Roma Tre University
26. INFN Sezione di Roma III
27. Astronomical Observatory of Capodimonte
28. University of Turin
29. INFN Sezione di Torino
30. Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano
31. Institute for High Energy Physics
32. INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00078, Monteporzio Catone, Italy
33. INFN Sezione di Napoli
34. University of Naples Federico II
35. Arcetri Astrophysical Observatory
36. Centre National d'Études Spatiales
37. Institut National de Physique Nucléaire et de Physique des Particules
38. University of Edinburgh
39. European Space Research Institute
40. European Space Astronomy Centre
41. University of Lyon System
42. École Polytechnique Fédérale de Lausanne
43. University of Lisbon
44. Institut d'Astrophysique Spatiale
45. INFN Sezione di Padova
46. Astrophysique, Instrumentation et Modélisation
47. Trieste Astronomical Observatory
48. Center for Particle Physics of Marseilles
49. National Institute for Astrophysics
50. Osservatorio Astronomico di Padova
51. University of Oslo
52. Jet Propulsion Lab
53. Technical University of Denmark
54. University of Paris
55. University College London
56. University of Helsinki
57. European Space Research and Technology Centre
58. Netherlands Institute for Radio Astronomy
59. University of Bonn
60. Durham University
61. Lagrange Laboratory
62. Aarhus University
63. Institute of Space Science
64. University of Chile
65. Institute for Fundamental Physics of the Universe
66. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
67. Infrared Processing and Analysis Center
68. California Institute of Technology
69. Brera Astronomical Observatory
70. Astroparticle and Cosmology Laboratory
71. University of Milan
72. INFN Sezione di Milano
73. INFN Sezione di Trieste
74. International School for Advanced Studies
75. Instituto de Astrofísica de Canarias
76. University of La Laguna
77. Research Institute in Astrophysics and Planetology
78. University of Trieste
79. University of Ferrara
80. RWTH Aachen University
81. University of California, Irvine
82. Institute of Space Sciences
83. INFN Sezione di Genova
84. Institute for Space Astrophysics and Planetology
85. Institute for Theoretical Physics
86. Lancaster University
87. Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres
88. Goddard Space Flight Center
89. Science Systems and Applications (United States)
90. Sapienza University of Rome
91. Heidelberg University
92. INAF-Sezione di Lecce, c/o Dipartimento Matematica e Fisica, Via per Arnesano, 73100, Lecce, Italy
93. INFN Sezione di Lecce
94. University of Salento
95. University of Zurich
96. Princeton University
97. University of Jyväskylä
98. Helsinki Institute of Physics

Abstract

Context. The Euclid mission is expected to discover thousands of z > 6 galaxies in three deep fields, which together will cover a ∼50 deg² 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 ∼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 ≤ 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 5σ detection threshold requirement in at least one of the Euclid near-infrared bands reduces the contamination fraction to 25%.

Copyright and License

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

Based on data products from observations conducted with ESO Telescopes at the Paranal Observatory under ESO program ID 179.A-2005 and on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. Also based in part on observations carried out with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Also based on observations carried out by NASA/ESA Hubble Space Telescope, obtained and archived at the Space Telescope Science Institute; and the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. SvM and KC acknowledge funding from the European Research Council through the award of the Consolidator Grant ID 681627-BUILDUP. PD acknowledges support from the European Research Council’s starting grant ERC StG-717001 (DELPHI), from the NWO grant 016.VIDI.189.162 (ODIN) and the European Commission’s and University of Groningen’s CO-FUND Rosalind Franklin program. The Euclid Consortium acknowledges the European Space Agency and a number of agencies and institutes that have supported the development of Euclid, in particular the Academy of Finland, the Agenzia Spaziale Italiana, the Belgian Science Policy, the Canadian Euclid Consortium, the French Centre National d’Etudes Spatiales, the Deutsches Zentrum für Luft- und Raumfahrt, the Danish Space Research Institute, the Fundação para a Ciência e a Tecnologia, the Ministerio de Economia y Competitividad, the National Aeronautics and Space Administration, the National Astronomical Observatory of Japan, the Netherlandse Onderzoekschool Voor Astronomie, the Norwegian Space Agency, the Romanian Space Agency, the State Secretariat for Education, Research and Innovation (SERI) at the Swiss Space Office (SSO), and the United Kingdom Space Agency. A complete and detailed list is available on the Euclid web site (http://www.euclid-ec.org). We thank Smaran Deshmukh for useful discussions on the SMUVS catalogue photometry. We thank Marc Sauvage for carefully reading the manuscript and providing constructive comments for the Euclid Consortium internal review.

Funding

SvM and KC acknowledge funding from the European Research Council through the award of the Consolidator Grant ID 681627-BUILDUP. PD acknowledges support from the European Research Council’s starting grant ERC StG-717001 (DELPHI), from the NWO grant 016.VIDI.189.162 (ODIN) and the European Commission’s and University of Groningen’s CO-FUND Rosalind Franklin program.

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