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.
author list (cited authors)
Reed, S. L., Banerji, M., Becker, G. D., Hewett, P. C., Martini, P., McMahon, R. G., ... Vikram, V.