Discovery and characterization of 25 new quasars at 4.6 &lt; <i>z</i> &lt; 6.9 from wide-field multiband surveys

Luminous quasars at z &gt;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&lt; z &lt;6.9 (six at z ≥6.5), with M 1450 between −25.4 and −27.0. We also present new spectra of six z &gt;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 (L 1.4 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&lt; z &lt;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 &gt;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 .

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Publication Details

Journal
Astronomy and Astrophysics
Published
2025-06-13
DOI
https://doi.org/10.1051/0004-6361/202554859
Citations
4
Primary Topic
Astronomy and Astrophysical Research
Type
article
Field-Weighted Citation Impact
4.77

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article

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

Masafusa Onoue, Fabian Walter, Jan–Torge Schindler, M. Bischetti et al.
4 citations
Astronomy and Astrophysics
Astronomy and Astrophysical Research
4.77
article

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

Masafusa Onoue, Fabian Walter, Jan–Torge Schindler, M. Bischetti, Jinyi Yang, Daniel Stern, S. Belladitta, J. Wolf, Zhang-Liang Xie, Feige Wang, Bram Venemans, Chiara Mazzucchelli, Frederick B. Davies, Emanuele Paolo Farina, L. N. Martínez-Ramírez, Silvia Onorato, Xiaohui Fan, Federica Loiacono, Roberto Decarli, Eduardo Ba nados, Tatevik Mkrtchyan
article en
4 citations

Abstract

Luminous quasars at z &gt;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&lt; z &lt;6.9 (six at z ≥6.5), with M 1450 between −25.4 and −27.0. We also present new spectra of six z &gt;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 (L 1.4 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&lt; z &lt;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 &gt;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 .

Astronomy and AstrophysicsVol. 699
National Science Foundation, Smithsonian Institution, National Aeronautics and Space Administration, W. M. Keck Foundation, Gordon and Betty Moore Foundation, Ohio State University, California Institute of Technology, University of Minnesota, Johns Hopkins University, University of Notre Dame, Space Telescope Science Institute, Queen's University Belfast, Durham University, Queen's University, Max-Planck-Gesellschaft, European Southern Observatory, Istituto Nazionale di Astrofisica, National Central University, Eötvös Loránd Tudományegyetem, China National Textile and Apparel Council, Agencia Nacional de Investigación y Desarrollo, Science Mission Directorate, Planetary Science Division, Lawrence Berkeley National Laboratory, Los Alamos National Laboratory
Openalex Percentile: Top 5%
Astronomy and Astrophysical Research
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