Gemini near-infrared spectroscopy of luminous z ∼ 6 quasars

Chemical abundances, black hole masses, and Mg II absorption

Linhua Jiang, Xiaohui Fan, Marianne Vestergaard, Jaron D. Kurk, Fabian Walter, Brandon C. Kelly, Michael A. Strauss

Research output: Contribution to journalArticle

142 Citations (Scopus)

Abstract

We present Gemini near-infrared spectroscopic observations of six luminous quasars at z = 5.8 to ∼6.3. Five of them were observed using Gemini South GNIRS, which provides a simultaneous wavelength coverage of 0.9-2.5 μm in cross-dispersion mode. The other source was observed in the K band with Gemini North NIRI. We calculate line strengths for all detected emission lines and use their ratios to estimate gas metallicity in the broad-line regions of the quasars. The metallicity is found to be supersolar, with a typical value of ∼4 Z, and a comparison with low-redshift observations shows no strong evolution in metallicity up to z ∼ 6. The Fe II/Mg II ratio of the quasars is 4.9 ± 1.4, consistent with low-redshift measurements. We estimate central black hole masses of 109-1010 M and Eddington luminosity ratios of order unity. We identify two Mg II λλ2796, 2803 absorbers with rest equivalent width W 0λ2796 > 1 Å at 2.2 < z < 3 and three Mg II absorbers with W0λ2796 > 1.5 Å at z > 3 in the spectra, with the two most distant absorbers at z = 4.8668 and 4.8823, respectively. The redshift number densities (dN/dz) of Mg II absorbers with W0λ2796 > 1.5 Å are consistent with no cosmic evolution up to z > 4.

Original languageEnglish (US)
Pages (from-to)1150-1161
Number of pages12
JournalAstronomical Journal
Volume134
Issue number3
DOIs
StatePublished - Sep 2007

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infrared spectroscopy
quasars
metallicity
absorbers
near infrared
estimates
extremely high frequencies
wavelength
unity
luminosity
gas
gases
wavelengths
chemical
comparison

Keywords

  • Galaxies: active
  • Galaxies: high-redshift
  • Quasars: absorption lines
  • Quasars: emission lines
  • Quasars: general

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Gemini near-infrared spectroscopy of luminous z ∼ 6 quasars : Chemical abundances, black hole masses, and Mg II absorption. / Jiang, Linhua; Fan, Xiaohui; Vestergaard, Marianne; Kurk, Jaron D.; Walter, Fabian; Kelly, Brandon C.; Strauss, Michael A.

In: Astronomical Journal, Vol. 134, No. 3, 09.2007, p. 1150-1161.

Research output: Contribution to journalArticle

Jiang, Linhua ; Fan, Xiaohui ; Vestergaard, Marianne ; Kurk, Jaron D. ; Walter, Fabian ; Kelly, Brandon C. ; Strauss, Michael A. / Gemini near-infrared spectroscopy of luminous z ∼ 6 quasars : Chemical abundances, black hole masses, and Mg II absorption. In: Astronomical Journal. 2007 ; Vol. 134, No. 3. pp. 1150-1161.
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AU - Kurk, Jaron D.

AU - Walter, Fabian

AU - Kelly, Brandon C.

AU - Strauss, Michael A.

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N2 - We present Gemini near-infrared spectroscopic observations of six luminous quasars at z = 5.8 to ∼6.3. Five of them were observed using Gemini South GNIRS, which provides a simultaneous wavelength coverage of 0.9-2.5 μm in cross-dispersion mode. The other source was observed in the K band with Gemini North NIRI. We calculate line strengths for all detected emission lines and use their ratios to estimate gas metallicity in the broad-line regions of the quasars. The metallicity is found to be supersolar, with a typical value of ∼4 Z⊙, and a comparison with low-redshift observations shows no strong evolution in metallicity up to z ∼ 6. The Fe II/Mg II ratio of the quasars is 4.9 ± 1.4, consistent with low-redshift measurements. We estimate central black hole masses of 109-1010 M ⊙ and Eddington luminosity ratios of order unity. We identify two Mg II λλ2796, 2803 absorbers with rest equivalent width W 0λ2796 > 1 Å at 2.2 < z < 3 and three Mg II absorbers with W0λ2796 > 1.5 Å at z > 3 in the spectra, with the two most distant absorbers at z = 4.8668 and 4.8823, respectively. The redshift number densities (dN/dz) of Mg II absorbers with W0λ2796 > 1.5 Å are consistent with no cosmic evolution up to z > 4.

AB - We present Gemini near-infrared spectroscopic observations of six luminous quasars at z = 5.8 to ∼6.3. Five of them were observed using Gemini South GNIRS, which provides a simultaneous wavelength coverage of 0.9-2.5 μm in cross-dispersion mode. The other source was observed in the K band with Gemini North NIRI. We calculate line strengths for all detected emission lines and use their ratios to estimate gas metallicity in the broad-line regions of the quasars. The metallicity is found to be supersolar, with a typical value of ∼4 Z⊙, and a comparison with low-redshift observations shows no strong evolution in metallicity up to z ∼ 6. The Fe II/Mg II ratio of the quasars is 4.9 ± 1.4, consistent with low-redshift measurements. We estimate central black hole masses of 109-1010 M ⊙ and Eddington luminosity ratios of order unity. We identify two Mg II λλ2796, 2803 absorbers with rest equivalent width W 0λ2796 > 1 Å at 2.2 < z < 3 and three Mg II absorbers with W0λ2796 > 1.5 Å at z > 3 in the spectra, with the two most distant absorbers at z = 4.8668 and 4.8823, respectively. The redshift number densities (dN/dz) of Mg II absorbers with W0λ2796 > 1.5 Å are consistent with no cosmic evolution up to z > 4.

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KW - Quasars: absorption lines

KW - Quasars: emission lines

KW - Quasars: general

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