Discovery and characterization of 25 new quasars at 4.6 < <i>z</i> < 6.9 from wide-field multiband surveys
S. Belladitta, Eduardo Ba nados, Zhang-Liang Xie, Roberto Decarli, Silvia Onorato, Jinyi Yang, M. Bischetti, Masafusa Onoue, Federica Loiacono, L. N. Martínez-Ramírez, Chiara Mazzucchelli, Frederick B. Davies, J. Wolf, Jan–Torge Schindler, Xiaohui Fan, Feige Wang, Fabian Walter, Tatevik Mkrtchyan, Daniel Stern, Emanuele Paolo Farina, Bram Venemans
Abstract
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 M 1450 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 (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< 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 .