Black hole mass estimates and emission-line properties of a sample of redshift z > 6.5 quasars
- Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
- Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- MIT-Kavli Center for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
- Department of Physics and Astronomy, Ohio University, Clippinger Lab 251B, Athens, OH 45701 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London, SW7 2AZ (United Kingdom)
- 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, Vol. 790, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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