Euclid Quick Data Release (Q1): Hunting for luminous z > 6 galaxies in the Euclid Deep Fields -- forecasts and first bright detections
Abstract
The evolution of the rest-frame ultraviolet luminosity function (UV LF) is a powerful probe of early star formation and stellar mass build-up. At z > 6, its bright end (MUV < -21) remains poorly constrained due to the small volumes of existing near-infrared (NIR) space-based surveys. The Euclid Deep Fields (EDFs) will cover 53 deg^2 with NIR imaging down to 26.5 AB, increasing area by a factor of 100 over previous space-based surveys. They thus offer an unprecedented opportunity to select bright z > 6 Lyman break galaxies (LBGs) and constrain the UV LF's bright end. With NIR coverage extending to 2um, Euclid can detect galaxies out to z = 13. We present forecasts for the number densities of z > 6 galaxies expected in the final EDF dataset. Using synthetic photometry from spectral energy distribution (SED) templates of z = 5--15 galaxies, z = 1--4 interlopers, and Milky Way MLT dwarfs, we explore optimal selection methods for high-z LBGs. A combination of S/N cuts with SED fitting (from optical to MIR) yields the highest-fidelity sample, recovering >76% of input z > 6 LBGs while keeping low-z contamination <10%. This excludes instrumental artefacts, which will affect early Euclid releases. Auxiliary data are critical: optical imaging from the Hyper Suprime-Cam and Vera C. Rubin Observatory distinguishes genuine Lyman breaks, while Spitzer/IRAC data help recover z > 10 sources. Based on empirical double power-law LF models, we expect >100,000 LBGs at z = 6-12 and >100 at z > 12 in the final Euclid release. In contrast, steeper Schechter models predict no z > 12 detections. We also present two ultra-luminous (MUV < -23.5) candidates from the EDF-N Q1 dataset. If their redshifts are confirmed, their magnitudes support a DPL LF model at z > 9, highlighting Euclid's power to constrain the UV LF's bright end and identify the most luminous early galaxies for follow-up.
Keywords
Cite
@article{arxiv.2511.02926,
title = {Euclid Quick Data Release (Q1): Hunting for luminous z > 6 galaxies in the Euclid Deep Fields -- forecasts and first bright detections},
author = {Euclid Collaboration and N. Allen and P. A. Oesch and R. A. A. Bowler and S. Toft and J. Matharu and J. R. Weaver and C. J. R. McPartland and M. Shuntov and D. B. Sanders and B. Mobasher and H. J. McCracken and H. Atek and E. Bañados and S. W. J. Barrow and S. Belladitta and D. Carollo and M. Castellano and C. J. Conselice and P. R. M. Eisenhardt and Y. Harikane and G. Murphree and M. Stefanon and S. M. Wilkins and A. Amara and S. Andreon and N. Auricchio and C. Baccigalupi and M. Baldi and A. Balestra and S. Bardelli and P. Battaglia and R. Bender and A. Biviano and E. Branchini and M. Brescia and J. Brinchmann and S. Camera and G. Cañas-Herrera and V. Capobianco and C. Carbone and J. Carretero and G. Castignani and S. Cavuoti and K. C. Chambers and A. Cimatti and C. Colodro-Conde and G. Congedo and L. Conversi and Y. Copin and F. Courbin and H. M. Courtois and M. Cropper and A. Da Silva and H. Degaudenzi and G. De Lucia and H. Dole and F. Dubath and C. A. J. Duncan and X. Dupac and S. Dusini and S. Escoffier and M. Farina and R. Farinelli and F. Faustini and S. Ferriol and F. Finelli and N. Fourmanoit and M. Frailis and E. Franceschi and M. Fumana and S. Galeotta and K. George and B. Gillis and C. Giocoli and J. Gracia-Carpio and A. Grazian and F. Grupp and S. V. H. Haugan and H. Hoekstra and W. Holmes and I. M. Hook and F. Hormuth and A. Hornstrup and K. Jahnke and M. Jhabvala and B. Joachimi and E. Keihänen and S. Kermiche and A. Kiessling and B. Kubik and K. Kuijken and M. Kümmel and M. Kunz and H. Kurki-Suonio and A. M. C. Le Brun and D. Le Mignant and S. Ligori and P. B. Lilje and V. Lindholm and I. Lloro and G. Mainetti and D. Maino and E. Maiorano and O. Mansutti and O. Marggraf and M. Martinelli and N. Martinet and F. Marulli and R. J. Massey and E. Medinaceli and S. Mei and Y. Mellier and M. Meneghetti and E. Merlin and G. Meylan and A. Mora and M. Moresco and L. Moscardini and R. Nakajima and C. Neissner and S. -M. Niemi and C. Padilla and S. Paltani and F. Pasian and K. Pedersen and W. J. Percival and V. Pettorino and S. Pires and G. Polenta and M. Poncet and L. A. Popa and L. Pozzetti and F. Raison and A. Renzi and J. Rhodes and G. Riccio and E. Romelli and M. Roncarelli and R. Saglia and Z. Sakr and D. Sapone and B. Sartoris and M. Schirmer and P. Schneider and T. Schrabback and A. Secroun and E. Sefusatti and G. Seidel and S. Serrano and P. Simon and C. Sirignano and G. Sirri and L. Stanco and J. Steinwagner and P. Tallada-Crespí and A. N. Taylor and H. I. Teplitz and I. Tereno and N. Tessore and R. Toledo-Moreo and F. Torradeflot and I. Tutusaus and L. Valenziano and J. Valiviita and T. Vassallo and Y. Wang and J. Weller and G. Zamorani and F. M. Zerbi and E. Zucca and V. Allevato and M. Ballardini and M. Bolzonella and E. Bozzo and C. Burigana and R. Cabanac and M. Calabrese and A. Cappi and D. Di Ferdinando and J. A. Escartin Vigo and L. Gabarra and W. G. Hartley and R. Maoli and J. Martín-Fleitas and S. Matthew and M. Maturi and N. Mauri and R. B. Metcalf and A. Pezzotta and M. Pöntinen and C. Porciani and I. Risso and V. Scottez and M. Sereno and M. Tenti and M. Viel and M. Wiesmann and Y. Akrami and I. T. Andika and S. Anselmi and M. Archidiacono and F. Atrio-Barandela and D. Bertacca and M. Bethermin and A. Blanchard and L. Blot and M. Bonici and M. L. Brown and S. Bruton and A. Calabro and B. Camacho Quevedo and F. Caro and C. S. Carvalho and T. Castro and F. Cogato and S. Conseil and T. Contini and A. R. Cooray and O. Cucciati and G. Desprez and A. Díaz-Sánchez and J. J. Diaz and S. Di Domizio and J. M. Diego and M. Y. Elkhashab and A. Enia and Y. Fang and A. G. Ferrari and A. Finoguenov and A. Fontana and F. Fontanot and A. Franco and K. Ganga and J. García-Bellido and T. Gasparetto and V. Gautard and E. Gaztanaga and F. Giacomini and F. Gianotti and G. Gozaliasl and M. Guidi and C. M. Gutierrez and A. Hall and S. Hemmati and C. Hernández-Monteagudo and H. Hildebrandt and J. Hjorth and J. J. E. Kajava and Y. Kang and V. Kansal and D. Karagiannis and K. Kiiveri and J. Kim and C. C. Kirkpatrick and S. Kruk and L. Legrand and M. Lembo and F. Lepori and G. Leroy and G. F. Lesci and J. Lesgourgues and T. I. Liaudat and S. J. Liu and X. Lopez Lopez and J. Macias-Perez and M. Magliocchetti and F. Mannucci and C. J. A. P. Martins and L. Maurin and M. Miluzio and P. Monaco and C. Moretti and G. Morgante and K. Naidoo and A. Navarro-Alsina and S. Nesseris and D. Paoletti and F. Passalacqua and K. Paterson and L. Patrizii and R. Pello and A. Pisani and D. Potter and S. Quai and M. Radovich and P. -F. Rocci and G. Rodighiero and S. Sacquegna and M. Sahlén and E. Sarpa and A. Schneider and M. Schultheis and D. Sciotti and E. Sellentin and F. Shankar and L. C. Smith and J. G. Sorce and K. Tanidis and C. Tao and G. Testera and R. Teyssier and S. Tosi and A. Troja and M. Tucci and C. Valieri and A. Venhola and D. Vergani and G. Verza and P. Vielzeuf and N. A. Walton and D. Scott},
journal= {arXiv preprint arXiv:2511.02926},
year = {2025}
}