Euclid preparation: XXI. Intermediate-redshift contaminants in the search for $z>6$ galaxies within the Euclid Deep Survey. (arXiv:2205.02871v3 [astro-ph.GA] UPDATED)

Euclid preparation: XXI. Intermediate-redshift contaminants in the search for $z>6$ galaxies within the Euclid Deep Survey. (arXiv:2205.02871v3 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Collaboration_Euclid/0/1/0/all/0/1">Euclid Collaboration</a>: <a href="http://arxiv.org/find/astro-ph/1/au:+Mierlo_S/0/1/0/all/0/1">S. E. van Mierlo</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Caputi_K/0/1/0/all/0/1">K. I. Caputi</a> (1 and 2), <a href="http://arxiv.org/find/astro-ph/1/au:+Ashby_M/0/1/0/all/0/1">M. Ashby</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Atek_H/0/1/0/all/0/1">H. Atek</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Bolzonella_M/0/1/0/all/0/1">M. Bolzonella</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Bowler_R/0/1/0/all/0/1">R. A. A. Bowler</a> (6 and 7), <a href="http://arxiv.org/find/astro-ph/1/au:+Brammer_G/0/1/0/all/0/1">G. Brammer</a> (2 and 8), <a href="http://arxiv.org/find/astro-ph/1/au:+Conselice_C/0/1/0/all/0/1">C. J. Conselice</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Cuby_J/0/1/0/all/0/1">J. Cuby</a> (9), <a href="http://arxiv.org/find/astro-ph/1/au:+Dayal_P/0/1/0/all/0/1">P. Dayal</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Diaz_Sanchez_A/0/1/0/all/0/1">A. Díaz-Sánchez</a> (10), <a href="http://arxiv.org/find/astro-ph/1/au:+Finkelstein_S/0/1/0/all/0/1">S. L. Finkelstein</a> (11), <a href="http://arxiv.org/find/astro-ph/1/au:+Hoekstra_H/0/1/0/all/0/1">H. Hoekstra</a> (12), <a href="http://arxiv.org/find/astro-ph/1/au:+Humphrey_A/0/1/0/all/0/1">A. Humphrey</a> (13), <a href="http://arxiv.org/find/astro-ph/1/au:+Ilbert_O/0/1/0/all/0/1">O. Ilbert</a> (9), <a href="http://arxiv.org/find/astro-ph/1/au:+McCracken_H/0/1/0/all/0/1">H. J. McCracken</a> (14), <a href="http://arxiv.org/find/astro-ph/1/au:+Milvang_Jensen_B/0/1/0/all/0/1">B. Milvang-Jensen</a> (2 and 8), <a href="http://arxiv.org/find/astro-ph/1/au:+Oesch_P/0/1/0/all/0/1">P. A. Oesch</a> (15 and 16), <a href="http://arxiv.org/find/astro-ph/1/au:+Pello_R/0/1/0/all/0/1">R. Pello</a> (9), <a href="http://arxiv.org/find/astro-ph/1/au:+Rodighiero_G/0/1/0/all/0/1">G. Rodighiero</a> (17), <a href="http://arxiv.org/find/astro-ph/1/au:+Schirmer_M/0/1/0/all/0/1">M. Schirmer</a> (18), <a href="http://arxiv.org/find/astro-ph/1/au:+Toft_S/0/1/0/all/0/1">S. Toft</a> (8 and 2), <a href="http://arxiv.org/find/astro-ph/1/au:+Weaver_J/0/1/0/all/0/1">J. R. Weaver</a> (2 and 8), <a href="http://arxiv.org/find/astro-ph/1/au:+Wilkins_S/0/1/0/all/0/1">S. M. Wilkins</a> (19), <a href="http://arxiv.org/find/astro-ph/1/au:+Willott_C/0/1/0/all/0/1">C. J. Willott</a> (20), <a href="http://arxiv.org/find/astro-ph/1/au:+Zamorani_G/0/1/0/all/0/1">G. Zamorani</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Amara_A/0/1/0/all/0/1">A. Amara</a> (21), <a href="http://arxiv.org/find/astro-ph/1/au:+Auricchio_N/0/1/0/all/0/1">N. Auricchio</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Baldi_M/0/1/0/all/0/1">M. Baldi</a> (22 and 5 and 23), <a href="http://arxiv.org/find/astro-ph/1/au:+Bender_R/0/1/0/all/0/1">R. Bender</a> (24 and 25), <a href="http://arxiv.org/find/astro-ph/1/au:+Bodendorf_C/0/1/0/all/0/1">C. Bodendorf</a> (24), <a href="http://arxiv.org/find/astro-ph/1/au:+Bonino_D/0/1/0/all/0/1">D. Bonino</a> (26), <a href="http://arxiv.org/find/astro-ph/1/au:+Branchini_E/0/1/0/all/0/1">E. Branchini</a> (27 and 28), <a href="http://arxiv.org/find/astro-ph/1/au:+Brescia_M/0/1/0/all/0/1">M. Brescia</a> (29), <a href="http://arxiv.org/find/astro-ph/1/au:+Brinchmann_J/0/1/0/all/0/1">J. Brinchmann</a> (13), <a href="http://arxiv.org/find/astro-ph/1/au:+Camera_S/0/1/0/all/0/1">S. Camera</a> (30 and 31 and 26), <a href="http://arxiv.org/find/astro-ph/1/au:+Capobianco_V/0/1/0/all/0/1">V. Capobianco</a> (26), <a href="http://arxiv.org/find/astro-ph/1/au:+Carbone_C/0/1/0/all/0/1">C. Carbone</a> (32), <a href="http://arxiv.org/find/astro-ph/1/au:+Carretero_J/0/1/0/all/0/1">J. Carretero</a> (33 and 34), et al. (166 additional authors not shown)

(Abridged) The Euclid mission is expected to discover thousands of z>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>6 galaxies challenging. 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. 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<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>6 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
minimized to 7% when including ultra-deep Rubin data. For UltraVISTA-like
bright galaxies, we find that Euclid (I-Y)>2.8 and (Y-J)<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-Y) colours. In
the most optimistic 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.

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