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arXiv · 2505.15923

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

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·Bram P. Venemans
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Abstract

Luminous quasars at $z>4$ provide key insights into the early Universe. Their rarity necessitates wide-field multi-band 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, complemented by literature-based quasar candidate catalogs. In this paper, we report the discovery of \nqsos\ new quasars at $4.6 6.5$ 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~\rm GHz}$$=0.09-1.0\times$10$^{34}$erg s$^{-1}$ Hz$^{-1}$). Among them, one source at $z=4.71$ exhibits typical blazar-like properties, including a flat radio spectrum, radio-loudness $\sim$1000, and multi-frequency variability. It is also detected by SRG/eROSITA X-ray telescope (f$_{\rm 0.2-2.3keV} \sim 1.3\times10^{-13}$erg s$^{-1}$ cm$^{-2}$). In addition, for seven $6.3 6$ quasars reported in the literature. A $z = 6.3$ quasar exhibits a velocity difference of approximately $9000$ km s$^{-1}$ between the C$\rm IV$ and Mg$\rm II$ emission lines, making it one of the most extreme C$\rm IV$ outflows currently known. Additionally, the sample includes three high-ionization broad absorption line quasars. One of these quasars shows potential evidence of an extremely fast outflow feature, reaching $48000$ km s$^{-1}$.

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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, Bram P. Venemans. 2025-05-21. Discovery and characterization of 25 new quasars at 4.6 < z < 6.9 from wide-field multi-band surveys. https://doi.org/10.1051/0004-6361%2F202554859

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