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

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 deg${}^2$ 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 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 $z\ge 7$, more than doubling the number of previously known quasars at $z\ge 7$. 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 $z\gtrsim 7$. The quasar with the highest-$z$, EUCL J172902.75+641018.1 at $z\approx 7.77$, 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.

Accepted for publication in A&A

References in corpus (49)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• EAZY: A Fast, Public Photometric Redshift Code
• A luminous quasar at a redshift of z = 7.085
• The Assembly of the First Massive Black Holes
• Euclid. I. Overview of the Euclid mission
• The LOFAR Two-metre Sky Survey -- V. Second data release
• A Luminous Quasar at Redshift 7.642
• A CEERS Discovery of an Accreting Supermassive Black Hole 570 Myr after the Big Bang: Identifying a Progenitor of Massive z > 6 Quasars
• JADES. The diverse population of infant Black Holes at 4<z<11: merging, tiny, poor, but mighty
• Pōniuā'ena: A Luminous $z=7.5$ Quasar Hosting a 1.5 Billion Solar Mass Black Hole
• Hydrogen reionisation ends by $z=5.3$: Lyman-$\alpha$ optical depth measured by the XQR-30 sample
• Reionization Era Bright Emission Line Survey: Selection and Characterization of Luminous Interstellar Medium Reservoirs in the z>6.5 Universe
• The UKIRT Hemisphere Survey: Definition and J-band Data Release
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 $\le$ z $\le$ 7.0
• Measurements of the z ~ 6 Intergalactic Medium Optical Depth and Transmission Spikes Using a New z > 6.3 Quasar Sample
• The Kinematics of z ~ 6 Quasar Host Galaxies
• The eROSITA Final Equatorial-Depth Survey (eFEDS): Identification and characterization of the counterparts to the point-like sources
• Euclid. III. The NISP Instrument
• The X-shooter/ALMA Sample of Quasars in the Epoch of Reionization. II. Black Hole Masses, Eddington Ratios, and the Formation of the First Quasars
• The X-SHOOTER/ALMA sample of Quasars in the Epoch of Reionization. I. NIR spectral modeling, iron enrichment and broad emission line properties
• Euclid. II. The VIS Instrument
• A wide dispersion in star formation rate and dynamical mass of 10^8 solar mass black hole host galaxies at redshift 6
• A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): JWST Reveals a Filamentary Structure around a z=6.61 Quasar
• (Nearly) Model-Independent Constraints on the Neutral Hydrogen Fraction in the Intergalactic Medium at $z\sim 5-7$ Using Dark Pixel Fractions in Ly$\alpha$ and Ly$\beta$ Forests
• Euclid preparation. XVIII. The NISP photometric system
• Euclid preparation: V. Predicted yield of redshift 7<z<9 quasars from the wide survey
• Quasar Luminosity Function at z = 7
• An extreme blue nugget, UV-bright starburst at z=3.613 with ninety per cent of Lyman continuum photon escape
• Discovery of 24 radio-bright quasars at $4.9\le z\le 6.6$ using low-frequency radio observations
• Deep silence: radio properties of little red dots
• Challenging the AGN scenario for JWST/NIRSpec LRD and non-LRD broad H$\alpha$ emitters in light of non-detection of NIRCam photometric variability and X-ray
• "Little red dots" cannot reside in the same dark matter halos as comparably luminous unobscured quasars
• A unified model for the clustering of quasars and galaxies at $z\approx 6$
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XI. Proximity Zone Analysis for Faint Quasar Spectra at z~6
• On the Connection between Supermassive Black Hole and Galaxy Growth in the Reionization Epoch
• A blazar in the epoch of reionization
• Another piece to the puzzle: radio detection of a JWST detected AGN candidate
• The SRG/eROSITA All-Sky Survey: X-ray beacons at late cosmic dawn
• A Little Red Dot at $\mathbf{z}=7.3$ within a Large Galaxy Overdensity
• Paving the Way for Euclid and JWST via Optimal Selection of High-z Quasars
• The CatSouth Quasar Candidate Catalog for the Southern Sky and a Unified All-Sky Catalog Based on Gaia DR3
• Updated dark pixel fraction constraints on reionization's end from the Lyman-series forests of XQR-30
• Optical and near-infrared spectroscopy of quasars at $z>6.5$: public data release and composite spectrum
• Euclid: The potential of slitless infrared spectroscopy: A z=5.4 quasar and new ultracool dwarfs
• Owl-z: a Bayesian tool to select z \geq 7 quasars
• 16 new quasars at the end of the reionization unveiled by self-supervised learning
• QUEST (Quasar Unsupervised Encoder and Synthesis Tool): A machine learning framework to generate quasar spectra