Cite this work
Žerjal et al. (2026).
Euclid Quick Data Release (Q1): A photometric search for ultracool dwarfs in the Euclid Deep Fields. A&A,
711.
@ARTICLE{2026A&A...711A..37Z,
author = {{{\v{Z}}erjal}, M. and {Dominguez-Tagle}, C. and {Vitas}, N. and {Sedighi}, N. and {Mart{\'\i}n}, E.~L. and {Zapatero Osorio}, M.~R. and {Olivares}, J. and {Mu{\~n}oz Torres}, S. and {Tsilia}, S. and {Zhang}, J.-Y. and {Barrado}, D. and {B{\'e}jar}, V.~J.~S. and {Bouy}, H. and {Burgasser}, A. and {Cruz}, P. and {Lodieu}, N. and {Mas Buitrago}, P. and {Phan-Bao}, N. and {Solano}, E. and {Tata}, R. and {Goldman}, B. and {Mohandasan}, A. and {Reyl{\'e}}, C. and {Smart}, R.~L. and {Aghanim}, N. and {Altieri}, B. and {Amara}, A. and {Andreon}, S. and {Auricchio}, N. and {Baccigalupi}, C. and {Baldi}, M. and {Balestra}, A. and {Bardelli}, S. and {Battaglia}, P. and {Biviano}, A. and {Bonchi}, A. and {Branchini}, E. and {Brescia}, M. and {Brinchmann}, J. and {Camera}, S. and {Ca{\~n}as-Herrera}, G. and {Capobianco}, V. and {Carbone}, C. and {Carretero}, J. and {Casas}, S. and {Castellano}, M. and {Castignani}, G. and {Cavuoti}, S. and {Chambers}, K.~C. and {Cimatti}, A. and {Colodro-Conde}, C. and {Congedo}, G. and {Conselice}, C.~J. and {Conversi}, L. and {Copin}, Y. and {Courbin}, F. and {Courtois}, H.~M. and {Cropper}, M. and {Cuby}, J.-G. and {Da Silva}, A. and {Degaudenzi}, H. and {De Lucia}, G. and {Dolding}, C. and {Dole}, H. and {Douspis}, M. and {Dubath}, F. and {Dupac}, X. and {Dusini}, S. and {Escoffier}, S. and {Farina}, M. and {Faustini}, F. and {Ferriol}, S. and {Fotopoulou}, S. and {Frailis}, M. and {Franceschi}, E. and {Galeotta}, S. and {George}, K. and {Gillis}, B. and {Giocoli}, C. and {G{\'o}mez-Alvarez}, P. and {Gracia-Carpio}, J. and {Granett}, B.~R. and {Grazian}, A. and {Grupp}, F. and {Haugan}, S.~V.~H. and {Hoar}, J. and {Holmes}, W. and {Hormuth}, F. and {Hornstrup}, A. and {Jahnke}, K. and {Jhabvala}, M. and {Keih{\"a}nen}, E. and {Kermiche}, S. and {Kiessling}, A. and {Kubik}, B. and {Kuijken}, K. and {K{\"u}mmel}, M. and {Kunz}, M. and {Kurki-Suonio}, H. and {Le Boulc'h}, Q. and {Le Brun}, A.~M.~C. and {Ligori}, S. and {Lilje}, P.~B. and {Lindholm}, V. and {Lloro}, I. and {Mainetti}, G. and {Maino}, D. and {Maiorano}, E. and {Mansutti}, O. and {Marggraf}, O. and {Martinelli}, M. and {Martinet}, N. and {Marulli}, F. and {Massey}, R. and {Medinaceli}, E. and {Mei}, S. and {Mellier}, Y. and {Meneghetti}, M. and {Merlin}, E. and {Meylan}, G. and {Mora}, A. and {Moresco}, M. and {Moscardini}, L. and {Nakajima}, R. and {Neissner}, C. and {Niemi}, S.-M. and {Padilla}, C. and {Paltani}, S. and {Pasian}, F. and {Pedersen}, K. and {Percival}, W.~J. and {Pettorino}, V. and {Pires}, S. and {Polenta}, G. and {Poncet}, M. and {Popa}, L.~A. and {Pozzetti}, L. and {Raison}, F. and {Rebolo}, R. and {Renzi}, A. and {Rhodes}, J. and {Riccio}, G. and {Romelli}, E. and {Roncarelli}, M. and {Saglia}, R. and {Sakr}, Z. and {Sapone}, D. and {Sartoris}, B. and {Schewtschenko}, J.~A. and {Schirmer}, M. and {Schneider}, P. and {Secroun}, A. and {Seidel}, G. and {Seiffert}, M. and {Serrano}, S. and {Simon}, P. and {Sirignano}, C. and {Sirri}, G. and {Stanco}, L. and {Steinwagner}, J. and {Tallada-Cresp{\'\i}}, P. and {Taylor}, A.~N. and {Tereno}, I. and {Toft}, S. and {Toledo-Moreo}, R. and {Torradeflot}, F. and {Tsyganov}, A. and {Tutusaus}, I. and {Valenziano}, L. and {Valiviita}, J. and {Vassallo}, T. and {Verdoes Kleijn}, G. and {Veropalumbo}, A. and {Wang}, Y. and {Weller}, J. and {Zacchei}, A. and {Zamorani}, G. and {Zerbi}, F.~M. and {Zucca}, E. and {Mart{\'\i}n-Fleitas}, J. and {Scottez}, V.},
title = "{Euclid: Quick Data Release (Q1) ─ A photometric search for ultracool dwarfs in the Euclid Deep Fields}",
journal = {\aap},
keywords = {catalogs, brown dwarfs, Solar and Stellar Astrophysics, Earth and Planetary Astrophysics, Astrophysics of Galaxies, Instrumentation and Methods for Astrophysics},
year = 2026,
month = jun,
volume = {711},
eid = {A37},
pages = {A37},
doi = {10.1051/0004-6361/202556980},
archivePrefix = {arXiv},
eprint = {2503.22497},
primaryClass = {astro-ph.SR},
adsurl = {https://ui.adsabs.harvard.edu/abs/2026A&A...711A..37Z},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
We present a catalogue of more than 5000 new ultracool dwarf (UCD) candidates in the three Euclid Deep Fields in the Q1 data release. They range from late M to late T dwarfs, and include 1200 L and T dwarfs. More than 100 of them have been spectroscopically confirmed, with seven of them being T dwarfs. Our UCD selection criteria are based only on colour (IE−YE>2.5). The combined requirement for optical detection and stringent signal-to-noise ratio threshold ensure a high purity of the sample, but at the expense of completeness, especially for T dwarfs. The detections range from magnitudes 19 and 24 in the near-infrared bands, and extend down to 26 in the optical band. The average surface density of detected UCDs on the sky is approximately 100 objects per deg2, including 20 L and T dwarfs per deg2. This leads to an expectation of at least 1.4 million ultracool dwarfs in the final data release of the Euclid Wide Survey, including at least 300,000 L dwarfs, and more than 2,600 T dwarfs, using the strict selection criteria from this work. We provide empirical Euclid colours as a function of spectral type, and a probability that an object with a given colour has a certain spectral type.
