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

B. Chehade, A. C. Carnall, T. Shanks, C. Diener, M. Fumagalli, J. R. Findlay, N. Metcalfe, J. Hennawi, C. Leibler, D. N. A. Murphy, J. X. Prochaska, M. J. Irwin, E. Gonzalez-Solares

Research output: Contribution to journalArticlepeer-review


Recently, Carnall et al. discovered two bright high-redshift quasars using the combination of the Very Large Telescope (VLT) Survey Telescope (VST) ATLAS and Wide-field Infrared Survey Explorer (WISE) surveys. The technique involved using the 3D colour plane iz : zW1 : 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 ≈2 × larger area of ≈3577 deg2 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 zAB = 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 Sloan Digital Sky Survey results of Jiang et al. at M1450 Å ≈ −27. Preliminary virial mass estimates based on the C iv and Mg ii emission lines give black hole masses in the range MBH ≈ 1–6 × 109 M for the four ATLAS quasars.
Original languageEnglish
Pages (from-to)1649-1659
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date19 Mar 2018
Publication statusPublished - 1 Aug 2018


  • astro-ph.GA
  • astro-ph.CO


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