Lai, SamuelSamuelLaiBian, FuyanFuyanBianOnken, Christopher A.Christopher A.OnkenWolf, ChristianChristianWolfMazzucchelli, ChiaraChiaraMazzucchelliBañados, EduardoEduardoBañadosBISCHETTI, ManuelaManuelaBISCHETTIBosman, Sarah E. I.Sarah E. I.BosmanBecker, GeorgeGeorgeBeckerCUPANI, GuidoGuidoCUPANID'ODORICO, ValentinaValentinaD'ODORICOEilers, Anna-ChristinaAnna-ChristinaEilersFan, XiaohuiXiaohuiFanFarina, Emanuele PaoloEmanuele PaoloFarinaOnoue, MasafusaMasafusaOnoueSchindler, Jan-TorgeJan-TorgeSchindlerWalter, FabianFabianWalterWang, FeigeFeigeWangYang, JinyiJinyiYangZhu, YongdaYongdaZhu2024-11-192024-11-1920220035-8711http://hdl.handle.net/20.500.12386/35387The elemental abundances in the broad-line regions of high-redshift quasars trace the chemical evolution in the nuclear regions of massive galaxies in the early Universe. In this work, we study metallicity-sensitive broad emission-line flux ratios in rest-frame UV spectra of 25 high-redshift (5.8 < z < 7.5) quasars observed with the VLT/X-shooter and Gemini/GNIRS instruments, ranging over $\log \left({{M}_{\rm {BH}}/\rm {M}_{\odot }}\right) = 8.4-9.8$ in black hole mass and $\log \left(\rm {L}_{\rm {bol}}/\rm {erg \, s}^{-1}\right) = 46.7-47.7$ in bolometric luminosity. We fit individual spectra and composites generated by binning across quasar properties: bolometric luminosity, black hole mass, and blueshift of the C IV line, finding no redshift evolution in the emission-line ratios by comparing our high-redshift quasars to lower redshift (2.0 < z < 5.0) results presented in the literature. Using CLOUDY-based locally optimally emitting cloud photoionization model relations between metallicity and emission-line flux ratios, we find the observable properties of the broad emission lines to be consistent with emission from gas clouds with metallicity that are at least 2-4 times solar. Our high-redshift measurements also confirm that the blueshift of the C IV emission line is correlated with its equivalent width, which influences line ratios normalized against C IV. When accounting for the C IV blueshift, we find that the rest-frame UV emission-line flux ratios do not correlate appreciably with the black hole mass or bolometric luminosity.STAMPAenArticle10.1093/mnras/stac10012-s2.0-85130449095https://academic.oup.com/mnras/article/513/2/1801/6566349http://arxiv.org/abs/2204.03335v12022MNRAS.513.1801LFIS/05 - ASTRONOMIA E ASTROFISICA