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 Very Large Telescope (VLT) Survey Telescope (VST) ATLAS and Wide-field Infrared Survey Explorer (WISE) surveys. The technique involved using the 3D 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 ≈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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2018
- DOI:
- 10.1093/mnras/sty690
- arXiv:
- arXiv:1803.01424
- Bibcode:
- 2018MNRAS.478.1649C
- Keywords:
-
- quasars: general;
- quasars: individual: VST-ATLAS J158.6938-14.4211;
- quasars: individual: VST-ATLAS J332.8017-32.1036;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 11 pages, 8 figures, 4 tables, accepted by MNRAS