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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 EuclidI_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 < 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.

Keywords
galaxies: active / galaxies: high-redshift / quasars: general / quasars: supermassive black holes / dark ages / reionization / first stars

Notes

This paper is published on behalf of the Euclid Consortium.

Astronomy & Astrophysics
Volume 711, Article Number A104, Number of pages 27
2026 July

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