Two more, bright, z > 6 quasars from VST ATLAS and WISE

Abstract

Recently, Carnall et al. discovered two bright high redshift quasars using the combination of the VST ATLAS and WISE surveys. The technique involved using the 3-D colour plane i-z:z-W1:W1-W2 with the WISE W1 (3.4 micron) and W2 (4.5 micron) bands taking the place of the usual NIR J band to help decrease stellar dwarf contamination. Here we report on our continued search for 5.7<z<6.4 quasars over an ~2x larger area of ~3577 sq. deg. of the Southern Hemisphere. We have found two further z>6 quasars, VST-ATLAS J158.6938-14.4211 at z=6.07 and J332.8017-32.1036 at z=6.32 with magnitudes of z_AB=19.4 and 19.7 mag respectively. J158.6938-14.4211 was confirmed by Keck LRIS observations and J332.8017-32.1036 was confirmed by ESO NTT EFOSC-2 observations. Here we present VLT X-shooter Visible and NIR spectra for the four ATLAS quasars. We have further independently rediscovered two z>5.7 quasars previously found by the VIKING/KiDS and PanSTARRS surveys. This means that in ATLAS we have now discovered a total of six quasars in our target 5.7<z<6.4 redshift range. Making approximate corrections for incompleteness, we find that our quasar space density agrees with the SDSS results of Jiang et al. at M_1450A~-27mag. Preliminary virial mass estimates based on the CIV and MIII emission lines give black hole masses in the range M_BH~1-6x10e9 M_solar for the four ATLAS quasars.

arXiv comment11 pages, 8 figures, 4 tables, accepted by MNRAS

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