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, 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.

doi:10.1051/0004-6361/202658883

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 deg(2) of sky covered during the first 1.5 years of the EuclidWide 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 Euclid I-E, Y-E, J(E), and H-E 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 < J(E) < 23.2 ( 25.5 < M-1450 < -23.6), extending quasar studies to the faint end of the quasar luminosity function (QLF) at z greater than or similar to 7. The quasar with the highest-z, EUCL J172902.75 + 641018.1 at z approximate to 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.

Yang, D., Hennawi, J.F., Guarneri, F., Wolf, J., Belladitta, S., Schindler, J.-T., et al. (2026). Euclid: Discovery of 31 new quasars at 6.6 < z< 7.8. ASTRONOMY & ASTROPHYSICS, 711 [10.1051/0004-6361/202658883].