No Redshift Evolution in the Broad-line-region Metallicity up to z = 7.54: Deep Near-infrared Spectroscopy of ULAS J1342+0928
Masafusa Onoue, Eduardo Bañados, Chiara Mazzucchelli, Bram P. Venemans, Jan-Torge Schindler, Fabian Walter, Joseph F. Hennawi, Irham Taufik Andika, Frederick B. Davies, Roberto Decarli, Emanuele P. Farina, Knud Jahnke, Tohru Nagao, Nozomu Tominaga, Feige Wang
Abstract
Abstract We present deep (9 hr) Gemini-N/Gemini Near-InfraRed Spectrograph near-infrared spectroscopic observations of ULAS J1342+0928, a luminous quasar at z = 7.54. Various broad emission lines were detected, as well as the underlying continuum and iron forests over the rest-frame wavelength 970–2930 Å. There is a clear trend that higher-ionization emission lines show larger blueshifts with C iv exhibiting km s −1 blueshift with respect to the systematic redshift from the far-infrared [C ii ] emission line. Those high-ionization lines have wide profiles with FWHM more than 10,000 km s −1 . A modest blueshift of km s −1 is also seen in Mg ii , the lowest-ionization line identified in the spectrum. The updated Mg ii -based black hole mass of and the Eddington ratio of confirm that ULAS J1342+0928 is powered by a massive and actively accreting black hole. There is no significant difference in the emission-line ratios such as Si iv /C iv and Al iii /C iv when compared to lower-redshift quasars in a similar luminosity range, which suggests early metal pollution of the broad-line-region clouds. This trend also holds for the Fe ii /Mg ii line ratio, known as a cosmic clock that traces the iron enrichment in the early universe. Different iron templates and continuum fitting ranges were used to explore how the Fe ii /Mg ii measurement changes as a function of spectral modeling. Quasars at even higher redshift or at fainter luminosity range ( erg s −1 ) are needed to probe the sites of early metal enrichment and a corresponding change in the Fe ii /Mg ii ratio.