Metallicity in Quasar Broad Line Regions at Redshift $\sim$ 6

Abstract

Broad line regions (BLRs) in high-redshift quasars provide crucial information of chemical enrichment in the early universe. Here we present a study of BLR metallicities in 33 quasars at redshift $5.7<z<6.4$. Using the near-IR spectra of the quasars obtained from the Gemini telescope, we measure their rest-frame UV emission line flux and calculate flux ratios. We then estimate BLR metallicities with empirical calibrations based on photoionization models. The inferred median metallicity of our sample is a few times the solar value, indicating that the BLR gas had been highly metal-enriched at $z\sim 6$. We compare our sample with a low-redshift quasar sample with similar luminosities and find no evidence of redshift evolution in quasar BLR metallicities. This is consistent with previous studies. The Fe II$/$Mg II flux ratio, a proxy for the Fe$/\alpha$ element abundance ratio, shows no redshift evolution as well, further supporting rapid nuclear star formation at $z\sim 6$. We also find that the black hole mass-BLR metallicity relation at $z\sim 6$ is consistent with the relation measured at $2<z<5$, suggesting that our results are not biased by a selection effect due to this relation.

ApJ, in press

References in corpus (32)

• A Catalog of Quasar Properties from SDSS DR7
• A luminous quasar at a redshift of z = 7.085
• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
• A Luminous Quasar at Redshift 7.642
• The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe
• Pōniuā'ena: A Luminous $z=7.5$ Quasar Hosting a 1.5 Billion Solar Mass Black Hole
• The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
• The Universal Relation of Galactic Chemical Evolution: The Origin of the Mass-Metallicity Relation
• Physical properties of 15 quasars at $z\gtrsim 6.5$
• Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
• Velocity-Metallicity Correlation for high-z DLA Galaxies: Evidence for a Mass-Metallicity Relation?
• Gemini Near-infrared Spectroscopy of Luminous z~6 Quasars: Chemical Abundances, Black Hole Masses, and MgII Absorption
• Fe II Emission in 14 Low-Redshift Quasars: I - Observations
• Black hole masses and enrichment of z ~ 6 SDSS quasars
• The MOSDEF Survey: Optical AGN Diagnostics at z~2.3
• The metallicity of the most distant quasars
• Size and properties of the narrow-line region in Seyfert-2 galaxies from spatially-resolved optical spectroscopy
• Three new VHS-DES Quasars at 6.7 < z < 6.9 and Emission Line Properties at z > 6.5
• The Nuclear Near-Infrared Spectral Properties of Nearby Galaxies
• The AGN Outflow in the HDFS Target QSO J2233-606 from a High-Resolution VLT/UVES Spectrum
• Eddington ratio governs the equivalent width of MgII emission line in active galactic nuclei
• No Redshift Evolution in the Broad Line Region Metallicity up to z=7.54: Deep NIR Spectroscopy of ULAS J1342+0928
• A Sample of Quasars with Strong Nitrogen Emission Lines from the Sloan Digital Sky Survey
• Improved Fe II emission line models for AGN using new atomic datasets
• Rapid Black Hole Growth at the Dawn of the Universe: A Super-Eddington Quasar at z=6.6
• The FeII/MgII flux ratio of low-luminosity quasars at z~3
• Semi-empirical metallicity calibrations based on ultraviolet emission lines of type-2 AGNs
• Chemical evolution of the Universe at 0.7 < z < 1.6 derived from abundance diagnostics of the broad-line region of quasars
• Strong Mg II and Fe II Absorbers at 2.2 < z < 6.0
• Mass-Metallicity Relation for Local Analogs of High-Redshift galaxies: Implications for the Evolution of the Mass-Metallicity Relations
• Multi-wavelength campaign on NGC 7469 V. Analysis of the HST/COS observations: Super solar metallicity, distance, and trough variation models

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• The Pan-STARRS1 z>5.6 quasar survey II: Discovery of 55 Quasars at 5.6<z<6.5
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