Three new VHS-DES quasars at 6.7 < z < 6.9 and emission line properties at z > 6.5
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2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. We report the results from a search for z > 6.5 quasars using the Dark Energy Survey (DES) Year 3 data set combined with the VISTA Hemisphere Survey (VHS) and WISE All-Sky Survey. Our photometric selection method is shown to be highly efficient in identifying clean samples of high-redshift quasars, leading to spectroscopic confirmation of three new quasars - VDES J0244-5008 (z = 6.724), VDES J0020-3653 (z = 6.834), and VDES J0246-5219 (z = 6.90) - which were selected as the highest priority candidates in the survey data without any need for additional follow-up observations. We have obtained spectroscopic observations in the near-infrared for VDES J0244-5008 and VDES J0020-3653 as well as our previously identified quasar, VDES J0224-4711 at z = 6.50 from Reed et al. We use the near-infrared spectra to derive virial black holemasses from the full width at half-maximum of the MgII line. These black hole masses are 1-2 109M. Combined with the bolometric luminosities of these quasars of Lbol 1-3 1047, these imply that the Eddington ratios are high, 0.6-1.1. We consider the C IV emission line properties of the sample and demonstrate that our highredshift quasars do not have unusual C IV line properties when compared to carefully matched low-redshift samples. Our new DES + VHS z > 6.5 quasars now add to the growing census of luminous, rapidly accreting supermassive black holes seen well into the epoch of reionization.
