Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8

Yang, D.; Hennawi, J. F.; Guarneri, F.; Wolf, J.; Belladitta, S.; Schindler, J. T.; Hughes, A. C.N.; Bañados, E.; Mortlock, D. J.; Yang, J.; Wang, F.; Fan, X.; Jahnke, K.; Stern, D.; Willott, C. J.; Barth, A. J.; Rottgering, H. J.A.; Varadaraj, R. G.; Decarli, R.; Eilers, A. C.; Ezziati, M.; Fu, Y.; Huang, J.; Jin, X.; Kang, Y.; Martinez-Ramirez, L. N.; Matsuoka, Y.; Onoue, M.; Pello, R.; Remigio, R. P.; Tee, W. L.; Venemans, B.; Vietri, G.; Wang, B.; Abbo, L. J.; Atek, H.; Bisogni, S.; Bosman, S. E.I.; Bowler, R. A.A.; Conselice, C. J.; Davies, F. B.; Gutierrez, C. M.; Harikane, Y.; Rubinur, K.; Lovell, C. C.; Magliocchetti, M.; Matthee, Jorryt J; Ricci, F.; Scialpi, M.; Scott, D.; Spinoglio, L.; Tarsitano, F.; Toba, Y.; Walter, F.; Weaver, J. R.; Zamorani, G.; Altieri, B.; Amara, A.; Andreon, S.; Aussel, H.; Baccigalupi, C.; Baldi, M.; Balestra, A.; Bardelli, S.; Battaglia, P.; Biviano, A.; Branchini, E.; Brescia, M.; Camera, S.; Cañas-Herrera, G.; Capobianco, V.; Carbone, C.; Carretero, J.; Castellano, M.; Castignani, G.; Cavuoti, S.; Chambers, K. C.; Cimatti, A.; Colodro-Conde, C.; Congedo, G.; Conversi, L.; Copin, Y.; Courbin, F.; Courtois, H. M.; Cropper, M.; Cuillandre, J. C.; Degaudenzi, H.; De Lucia, G.; Dolding, C.; Dole, H.; Douspis, M.; Dubath, F.; Dupac, X.; Dusini, S.; Escoffier, S.; Farina, M.; Farinelli, R.; Ferriol, S.; Finelli, F.; Fourmanoit, N.; Frailis, M.; Franceschi, E.; Fumana, M.; Galeotta, S.; George, K.; Gillis, B.; Giocoli, C.; Gómez-Alvarez, P.; Gracia-Carpio, J.; Grazian, A.; Grupp, F.; Guzzo, L.; Gwyn, S.; Haugan, S. V.H.; Hoekstra, H.; Holmes, W.; Hook, I. M.; Hormuth, F.; Hornstrup, A.; Jhabvala, M.; Kermiche, S.; Kubik, B.; Kuijken, K.; Kümmel, M.; Kunz, M.; Kurki-Suonio, H.; Le Brun, A. M.C.; Ligori, S.; Lilje, P. B.; Lindholm, V.; Lloro, I.; Mainetti, G.; Maino, D.; Maiorano, E.; Mansutti, O.; Marggraf, O.; Martinelli, M.; Martinet, N.; Marulli, F.; Massey, R. J.; Mccracken, H. J.; Medinaceli, E.; Mei, S.; Mellier, Y.; Meneghetti, M.; Merlin, E.; Meylan, G.; Mohr, J. J.; Mora, A.; Moresco, M.; Moscardini, L.; Munari, E.; Nakajima, R.; Neissner, C.; Nichol, R. C.; Niemi, S. M.; Padilla, C.; Paltani, S.; Pasian, F.; Pedersen, K.; Percival, W. J.; Pettorino, V.; Pires, S.; Polenta, G.; Poncet, M.; Popa, L. A.; Pozzetti, L.; Racca, G. D.; Raison, F.; Rebolo, R.; Renzi, A.; Rhodes, J.; Riccio, G.; Rix, H. W.; Romelli, E.; Roncarelli, M.; Rosset, C.; Rusholme, B.; Saglia, R.; Sakr, Z.; Sapone, D.; Sauvage, M.; Schirmer, M.; Schneider, P.; Schrabback, T.; Secroun, A.; Seidel, G.; Serrano, S.; Sihvola, E.; Simon, P.; Sirignano, C.; Sirri, G.; Stanco, L.; Steinwagner, J.; Tallada-Crespí, P.; Tereno, I.; Tessore, N.; Toft, S.; Toledo-Moreo, R.; Torradeflot, F.; Tutusaus, I.; Valenziano, L.; Valiviita, J.; Vassallo, T.; Wang, Y.; Weller, J.; Zerbi, F. M.; Zucca, E.; Fabbian, G.; Huertas-Company, M.; Martín-Fleitas, J.; Monaco, P.; Scottez, V.; Viel, M.

Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8

Yang D et al. 2026. Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8. Astronomy and Astrophysics. 711, A104.

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DOI

10.1051/0004-6361/202658883

Journal Article | Published | English

Scopus indexed

Author

Yang, D.; Hennawi, J. F.; Guarneri, F.; Wolf, J.; Belladitta, S.; Schindler, J. T.; Hughes, A. C.N.; Bañados, E.; Mortlock, D. J.; Yang, J.; Wang, F.; Fan, X.
All

Department

Matthee Group

Abstract

We report the discovery of 31 new high-z quasars in the redshift range 6.6 < z < 7.8. These quasars were selected from approximately 3000 deg2 of sky covered during the first 1.5 years of the Euclid Wide Survey, representing the initial results of the Euclid high-z quasar search. Our candidate selection employed multiple machine-learning and probabilistic techniques applied to the EuclidIE, YE, JE, and HE images, supplemented by ancillary z-band data when available. Spectroscopic follow-up observations were carried out with Keck, Magellan, and the Large Binocular Telescope (LBT). Among the new discoveries, there are 12 quasars at z ≥ 7, more than doubling the number of previously known quasars at z ≥ 7. The newly discovered quasars exhibit 21.2 < JE < 23.2 (−25.5 < M1450 < −23.6), extending quasar studies to the faint end of the quasar luminosity function (QLF) at z ≳ 7. The quasar with the highest-z, EUCL J172902.75+641018.1 at z ≈ 7.77, sets the new redshift record for the most distant quasar ever reported. These discoveries demonstrate Euclid’s transformative role in high-z quasar discovery and set the stage for future follow-up studies of the early galaxies hosting quasars, supermassive black hole growth, and the intergalactic medium in the epoch of reionisation.

Publishing Year

2026

Date Published

2026-07-01

Journal Title

Astronomy and Astrophysics

Publisher

EDP Sciences

Acknowledgement

D. Yang acknowledges helpful discussions with members of the ENIGMA group at UC Santa Barbara and Leiden University, in particular Elia Pizzati, Silvia Onorato, and Diego González for their valuable feedback. D. Yang thanks Shane Bechtel for assistance during observations, and acknowledges the early contributions of Riccardo Nanni, which helped lay the foundation for this work. D. Yang and J. F. Hennawi acknowledge support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No 885301). J. F. Hennawi acknowledges support from NSF grant No. 2307180. F. Guarneri and J.-T. Schindler are supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number 518006966. F. Wang acknowledges support from NSF award AST-2513040. R. Decarli acknowledges support from the INAF GO 2022 grant “The birth of the giants: JWST sheds light on the build-up of quasars at cosmic dawn”, INAF Minigrant 2024 “The interstellar medium at high redshift”, and by the PRIN MUR “2022935STW”, RFF M4.C2.1.1, CUP J53D23001570006 and C53D23000950006. S. E. I. Bosman is supported by the Deutsche Forschungsgemeinschaft (DFG) under Emmy Noether grant number BO 5771/1-1. Y. Harikane acknowledges support from the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (24H00245), the JSPS Core-to-Core Program (JPJSCCA20210003), and the JSPS International Leading Research (22K21349). J. R. Weaver acknowledges that support for this work was provided by The Brinson Foundation through a Brinson Prize Fellowship grant. 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 Agenzia Spaziale Italiana, the Austrian Forschungsförderungsgesellschaft funded through BMIMI, the Belgian Science Policy, the Canadian Euclid Consortium, the Deutsches Zentrum für Luft- und Raumfahrt, the DTU Space and the Niels Bohr Institute in Denmark, the French Centre National d’Etudes Spatiales, the Fundação para a Ciência e a Tecnologia, the Hungarian Academy of Sciences, the Ministerio de Ciencia, Innovación y Universidades, the National Aeronautics and Space Administration, the National Astronomical Observatory of Japan, the Netherlandse Onderzoekschool Voor Astronomie, the Norwegian Space Agency, the Research Council of Finland, 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 (www.euclid-ec.org). Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognise and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. This work uses LBT data from programmes: MPIA-2025A-007 and MPIA-2025B-004. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia, LOFAR data products were provided by the LOFAR Surveys Key Science project (LSKSP; https://lofar-surveys.org/) and were derived from observations with the International LOFAR Telescope (ILT). LOFAR is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, which are owned by various parties (each with their own funding sources), and which are collectively operated by the ILT foundation under a joint scientific policy. The efforts of the LSKSP have benefited from funding from the European Research Council, NOVA, NWO, CNRS-INSU, the SURF Co-operative, the UK Science and Technology Funding Council and the Jülich Supercomputing Centre. We make use of z-band imaging from the Wide Imaging with Subaru HSC of the Euclid Sky (WISHES) program operated by the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We also make use of z-band imaging from the Dark Energy Survey (DES), based on observations obtained at the Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by AURA under a cooperative agreement with the National Science Foundation. This work made use of NumPy (Harris et al. 2020), SciPy (Virtanen et al. 2020), Astropy (Astropy Collaboration 2013, 2018, 2022), PypeIt (Prochaska et al. 2020), Sculptor (Schindler 2022), condXD (Kang et al. 2025), pysersic (Pasha & Miller 2023), Matplotlib (Hunter 2007), corner.py (Foreman-Mackey 2016), healpy (Zonca et al. 2020).

Volume

711

Article Number

A104

ISSN

0004-6361

eISSN

1432-0746

IST-REx-ID

23044

Cite this

Yang D, Hennawi JF, Guarneri F, et al. Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8. Astronomy and Astrophysics. 2026;711. doi:10.1051/0004-6361/202658883

Yang, D., Hennawi, J. F., Guarneri, F., Wolf, J., Belladitta, S., Schindler, J. T., … Viel, M. (2026). Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8. Astronomy and Astrophysics. EDP Sciences. https://doi.org/10.1051/0004-6361/202658883

Yang, D., J. F. Hennawi, F. Guarneri, J. Wolf, S. Belladitta, J. T. Schindler, A. C.N. Hughes, et al. “Euclid: Discovery of 31 New Quasars at 6.6 < z < 7.8.” Astronomy and Astrophysics. EDP Sciences, 2026. https://doi.org/10.1051/0004-6361/202658883.

D. Yang et al., “Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8,” Astronomy and Astrophysics, vol. 711. EDP Sciences, 2026.

Yang D et al. 2026. Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8. Astronomy and Astrophysics. 711, A104.

Yang, D., et al. “Euclid: Discovery of 31 New Quasars at 6.6 < z < 7.8.” Astronomy and Astrophysics, vol. 711, A104, EDP Sciences, 2026, doi:10.1051/0004-6361/202658883.

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