Eight new luminous z > 6 quasars selected via SED model fitting of VISTA, WISE and Dark Energy Survey Year 1 Observations

S. L. Reed, R. G. McMahon, P. Martini, M. Banerji, M. Auger, P. C. Hewett, S. E. Koposov, S. L. J. Gibbons, E. Gonzalez-Solares, F. Ostrovski, S. S. Tie, F. B. Abdalla, S. Allam, A. Benoit-Levy, E. Bertin, D. Brooks, E. Buckley-Geer, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, L. N. da Costa, D. L. DePoy, S. Desai, H. T. Diehl, P. Doel, A. E. Evrard, D. A. Finley, B. Flaugher, P. Fosalba, J. Frieman, J. Garcıa-Bellido, E. Gaztanaga, D. A. Goldstein, D. Gruen, R. A. Gruendl, G. Gutierrez, D. J. James, K. Kuehn, N. Kuropatkin, O. Lahav, M. Lima, M. A. G. Maia, J. L. Marshall, P. Melchior, C. J. Miller, R. Miquel, B. Nord, R. Ogando, A. A. Plazas, A. K. Romer, E. Sanchez, V. Scarpine, M. Schubnell, I. Sevilla-Noarbe, R. C. Smith, F. Sobreira, E. Suchyta, M. E. C. Swanson, G. Tarle, D. L. Tucker, A. R. Walker, W. Wester

Published 2017-01-17Version 1

We present the discovery and spectroscopic confirmation with the ESO NTT and Gemini South telescopes of eight new 6.0 < z < 6.5 quasars with z$_{AB}$ < 21.0. These quasars were photometrically selected without any star-galaxy morphological criteria from 1533 deg$^{2}$ using SED model fitting to photometric data from the Dark Energy Survey (g, r, i, z, Y), the VISTA Hemisphere Survey (J, H, K) and the Wide-Field Infrared Survey Explorer (W1, W2). The photometric data was fitted with a grid of quasar model SEDs with redshift dependent Lyman-{\alpha} forest absorption and a range of intrinsic reddening as well as a series of low mass cool star models. Candidates were ranked using on a SED-model based $\chi^{2}$-statistic, which is extendable to other future imaging surveys (e.g. LSST, Euclid). Our spectral confirmation success rate is 100% without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants the method allows large data sets to be processed without human intervention and without being over run by spurious false candidates. We also present a robust parametric redshift estimating technique that gives comparable accuracy to MgII and CO based redshift estimators. We find two z $\sim$ 6.2 quasars with HII near zone sizes < 3 proper Mpc which could indicate that these quasars may be young with ages < 10$^6$ - 10$^7$ years or lie in over dense regions of the IGM. The z = 6.5 quasar VDESJ0224-4711 has J$_{AB}$ = 19.75 is the second most luminous quasar known with z > 6.5.