Black hole mass estimates and emission-line properties of a sample of redshift z > 6.5 quasars

Journal Article · Fri Aug 01 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/790/2/145· OSTI ID:22365462

De Rosa, Gisella; Peterson, Bradley M.; Frank, Stephan ^[1]; Venemans, Bram P.; Decarli, Roberto; Walter, Fabian ^[2]; Gennaro, Mario ^[3]; Simcoe, Robert A. ^[4]; Dietrich, Matthias ^[5]; McMahon, Richard G.; Hewett, Paul C. ^[6]; Mortlock, Daniel J. ^[7]; Simpson, Chris ^[8]

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1. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
2. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
3. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
4. MIT-Kavli Center for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
5. Department of Physics and Astronomy, Ohio University, Clippinger Lab 251B, Athens, OH 45701 (United States)
6. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
7. Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London, SW7 2AZ (United Kingdom)
8. Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom)

We present the analysis of optical and near-infrared spectra of the only four z > 6.5 quasars known to date, discovered in the UKIDSS-LAS and VISTA-VIKING surveys. Our data set consists of new Very Large Telescope/X-Shooter and Magellan/FIRE observations. These are the best optical/NIR spectroscopic data that are likely to be obtained for the z > 6.5 sample using current 6-10 m facilities. We estimate the black hole (BH) mass, the Eddington ratio, and the Si IV/C IV, C III]/C IV, and Fe II/Mg II emission-line flux ratios. We perform spectral modeling using a procedure that allows us to derive a probability distribution for the continuum components and to obtain the quasar properties weighted upon the underlying distribution of continuum models. The z > 6.5 quasars show the same emission properties as their counterparts at lower redshifts. The z > 6.5 quasars host BHs with masses of ∼10{sup 9} M{sub ☉} that are accreting close to the Eddington luminosity ((log(L{sub Bol}/L{sub Edd})) = –0.4 ± 0.2), in agreement with what has been observed for a sample of 4.0 < z < 6.5 quasars. By comparing the Si IV/C IV and C III]/C IV flux ratios with the results obtained from luminosity-matched samples at z ∼ 6 and 2 ≤ z ≤ 4.5, we find no evidence of evolution of the line ratios with cosmic time. We compare the measured Fe II/Mg II flux ratios with those obtained for a sample of 4.0 < z < 6.4 sources. The two samples are analyzed using a consistent procedure. There is no evidence that the Fe II/Mg II flux ratio evolves between z = 7 and z = 4. Under the assumption that the Fe II/Mg II traces the Fe/Mg abundance ratio, this implies the presence of major episodes of chemical enrichment in the quasar hosts in the first ∼0.8 Gyr after the Big Bang.

• OSTI ID: 22365462
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 790; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BLACK HOLES
CARBON
COMPARATIVE EVALUATIONS
DISTRIBUTION
EDDINGTON THEORY
ELEMENT ABUNDANCE
EMISSION
GALAXIES
INFRARED SPECTRA
IRON
LUMINOSITY
MASS
NEAR INFRARED RADIATION
QUASARS
RED SHIFT
SILICON
SPECTROSCOPY
TELESCOPES
VISIBLE RADIATION