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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 709927.0, MPI für Astronomie / Publikationen_mpia
Black hole mass estimates and emission-line properties of a sample of redshift z > 6.5 quasars
Authors:De Rosa, G.; Venemans, B. P.; Decarli, R.; Gennaro, M.; Simcoe, R. A.; Dietrich, M.; Peterson, B. M.; Walter, F.; Frank, S.; McMahon, R. G.; Hewett, P. C.; Mortlock, D. J.; Simpson, C.
Date of Publication (YYYY-MM-DD):2014
Title of Journal:The Astrophysical Journal
Issue / Number:2
Start Page:id. 145 (14 pp)
Audience:Not Specified
Abstract / Description: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 ~109 M &sun; that are accreting close to the Eddington luminosity (langlog(L Bol/L Edd)rang = -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. Based on observations collected at the European Southern Observatory, Chile, programs 286.A-5025, 087.A-0890, and 088.A-0897. This paper also includes data gathered with the 6.5 m Magellan Telescope located at Las Campanas Observatory, Chile.
Free Keywords:galaxies: high-redshift; quasars: emission lines
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0004-637X %R 10.1088/0004-637X/790/2/145
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