BLACK HOLE MASS ESTIMATES AND EMISSION-LINE PROPERTIES OF A SAMPLE OF REDSHIFT z > 6.5 QUASARS
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Rosa-2014-BLACK HOLE MASS ESTI.pdf
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1.36 MB
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Author(s)
Simcoe, Robert A.
Date Issued
July 2014
Journal
The Astrophysical Journal
Publisher
IOP Publishing
Citation
De Rosa, Gisella, Bram P. Venemans, Roberto Decarli, Mario Gennaro, Robert A. Simcoe, Matthias Dietrich, Bradley M. Peterson, et al. “ BLACK HOLE MASS ESTIMATES AND EMISSION-LINE PROPERTIES OF A SAMPLE OF REDSHIFT z > 6.5 QUASARS .” The Astrophysical Journal 790, no. 2 (July 16, 2014): 145. © 2014 The American Astronomical Society
Version
Final published version
Abstract
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[superscript 9] M [subscript ☉] that are accreting close to the Eddington luminosity ( = –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.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1088/0004-637x/790/2/145
