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arXiv · 1311.3260

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

G. De Rosa·B. P. Venemans·R. Decarli·M. Gennaro·R. A. Simcoe·M. Dietrich·B. M. Peterson·F. Walter·S. Frank·R. G. McMahon·P. C. Hewett·D. J. Mortlock·C. Simpson
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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 VLT/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 mass, the Eddington ratio, and the SiIV/CIV, CIII]/CIV, and FeII/MgII 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 black holes with masses of $\sim 10^9$ M$_{\odot}$ that are accreting close to the Eddington luminosity ($\langle{\rm log} (L_{\rm Bol}/L_{\rm Edd})\rangle= -0.4\pm0.2$), in agreement with what has been observed for a sample of $4.0<z<6.5$ quasars. By comparing the SiIV/CIV and CIII]/CIV flux ratios with the results obtained from luminosity-matched samples at $z\sim6$ and $2\leq z\leq4.5$, we find no evidence of evolution of the line ratios with cosmic time. We compare the measured FeII/MgII 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 FeII/MgII flux ratio evolves between $z=7$ and $z=4$. Under the assumption that the FeII/MgII traces the Fe/Mg abundance ratio, this implies the presence of major episodes of chemical enrichment in the quasar hosts in the first $\sim0.8$ Gyr after the Big Bang.

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G. De Rosa, B. P. Venemans, R. Decarli, M. Gennaro, R. A. Simcoe, M. Dietrich, B. M. Peterson, F. Walter, S. Frank, R. G. McMahon, P. C. Hewett, D. J. Mortlock, C. Simpson. 2013-11-13. Black hole mass estimates and emission-line properties of a sample of redshift z>6.5 quasars. https://doi.org/10.1088/0004-637x/790/2/145

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