No Redshift Evolution in the Broad-line-region Metallicity up to z = 7.54: Deep Near-infrared Spectroscopy of ULAS J1342+0928
Journal
Date Issued
2020
Author(s)
Onoue, Masafusa
•
Bañados, Eduardo
•
Mazzucchelli, Chiara
•
Venemans, Bram P.
•
Schindler, Jan-Torge
•
Walter, Fabian
•
Hennawi, Joseph F.
•
Andika, Irham Taufik
•
Davies, Frederick B.
•
•
Farina, Emanuele P.
•
Jahnke, Knud
•
Nagao, Tohru
•
Tominaga, Nozomu
•
Wang, Feige
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 $\lambda 1549$ exhibiting ${5510}_{-110}^{+240}$ km s-1 blueshift with respect to the systematic redshift from the far-infrared [C II] $158\,\mu {\rm{m}}$ emission line. Those high-ionization lines have wide profiles with FWHM more than 10,000 km s-1. A modest blueshift of ${340}_{-80}^{+110}$ 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 ${M}_{\mathrm{BH}}={9.1}_{-1.3}^{+1.4}\times {10}^{8}{M}_{\odot }$ and the Eddington ratio of ${L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}}={1.1}_{-0.2}^{+0.2}$ 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 ( ${L}_{\mathrm{bol}}\lesssim {10}^{46}$ erg s-1) are needed to probe the sites of early metal enrichment and a corresponding change in the Fe II/Mg II ratio.
Volume
898
Issue
2
Start page
105
Issn Identifier
0004-637X
Ads BibCode
2020ApJ...898..105O
Rights
open.access
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