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Discovery and characterization of 25 new quasars at 4.6 < z < 6.9 from wide-field multiband surveys

Luminous quasars at z>4 provide key insights into the early Universe. Their rarity necessitates wide-field multiband surveys to efficiently separate them from the main astrophysical contaminants (i.e., ultracool dwarfs). To expand the sample of high-z quasars, we conducted targeted selections usi...

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Main Authors: Belladitta, Silvia (Author) , Bañados Torres, Eduardo (Author) , Xie, Zhang-Liang (Author) , Decarli, Roberto (Author) , Onorato, Silvia (Author) , Yang, Jinyi (Author) , Bischetti, Manuela (Author) , Onoue, Masafusa (Author) , Loiacono, Federica (Author) , Martínez-Ramírez, Laura N. (Author) , Mazzucchelli, Chiara (Author) , Davies, Frederick B. (Author) , Wolf, Julien (Author) , Schindler, Jan-Torge (Author) , Fan, Xiaohui (Author) , Wang, Feige (Author) , Walter, Fabian (Author) , Mkrtchyan, Tatevik (Author) , Stern, Daniel (Author) , Farina, Emanuele P. (Author) , Venemans, Bram P. (Author)
Format: Article (Journal)
Language:English
Published: 23 July 2025
In: Astronomy and astrophysics
Year: 2025, Volume: 699, Pages: 1-23
ISSN:1432-0746
DOI:10.1051/0004-6361/202554859
Online Access:Verlag, kostenfrei, Volltext: https://doi.org/10.1051/0004-6361/202554859
Verlag, kostenfrei, Volltext: https://www.aanda.org/articles/aa/abs/2025/07/aa54859-25/aa54859-25.html
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Author Notes:Silvia Belladitta, Eduardo Bañados, Zhang-Liang Xie, Roberto Decarli, Silvia Onorato, Jinyi Yang, Manuela Bischetti, Masafusa Onoue, Federica Loiacono, Laura N. Martínez-Ramírez, Chiara Mazzucchelli, Frederick B. Davies, Julien Wolf, Jan-Torge Schindler, Xiaohui Fan, Feige Wang, Fabian Walter, Tatevik Mkrtchyan, Daniel Stern, Emanuele P. Farina, and Bram P. Venemans
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Summary:Luminous quasars at z>4 provide key insights into the early Universe. Their rarity necessitates wide-field multiband surveys to efficiently separate them from the main astrophysical contaminants (i.e., ultracool dwarfs). To expand the sample of high-z quasars, we conducted targeted selections using optical, infrared, and radio surveys, which we complemented by literature-based quasar candidate catalogs. We report the discovery of 25 new quasars at 4.6<z<6.9 (six at z≥6.5), with M1450 between −25.4 and −27.0. We also present new spectra of six z>6.5 quasars we selected, but whose independent discovery has already been published in the literature. Three of the newly discovered quasars are strong radio emitters (L1.4 GHz = 0.09−1.0×10 34 erg s −1 Hz−1). One source at z = 4.71 exhibits typical blazar-like properties, including a flat radio spectrum, a radio loudness of ∼1000, and multifrequency variability. It was also detected by SRG/eROSITA X-ray telescope (f 0.2−2.3 keV∼1.3×10 −13 erg s −1< cm −2). In addition, for seven 6.3<z<6.9 quasars, we present near-infrared spectroscopy and estimated the central black hole mass from their C IV and Mg II broad emission lines. Their masses (log[M BH,MgII] = 8.58−9.14 M⊙) and Eddington ratios (λ Edd,MgII = 0.74−2.2) are consistent with other z>6 quasars reported in the literature. A z = 6.3 quasar exhibits a velocity difference of approximately 9000 km s −1 between the C IV and Mg II emission lines. This means that it is one of the most extreme C IV outflows currently known. The sample also includes three high-ionization broad absorption line (HiBAL) quasars. One of these quasars shows potential evidence of an extremely fast outflow feature that reaches 47 000 km s -1.
Item Description:Gesehen am 17.12.2025
Physical Description:Online Resource
ISSN:1432-0746
DOI:10.1051/0004-6361/202554859

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