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Two bright z > 6 quasars from VST ATLAS and a new method of optical plus mid-infrared colour selection

Carnall, A.C.; Shanks, T.; Chehade, B.; Fumagalli, M.; Rauch, M.; Irwin, M.J.; Gonzalez-Solares, E.; Findlay, J.R.; Metcalfe, N.

Two bright z > 6 quasars from VST ATLAS and a new method of optical plus mid-infrared colour selection Thumbnail


Authors

A.C. Carnall

T. Shanks

B. Chehade

M. Rauch

M.J. Irwin

E. Gonzalez-Solares

J.R. Findlay



Abstract

We present the discovery of two z > 6 quasars, selected as i-band dropouts in the Very Large Telescope Survey Telescope ATLAS survey. Our first quasar has redshift, z = 6.31 ± 0.03, z-band magnitude, zAB = 19.63 ± 0.08 and rest frame 1450 Å absolute magnitude, M1450 = −27.8 ± 0.2, making it the joint second most luminous quasar known at z > 6. The second quasar has z = 6.02 ± 0.03, zAB = 19.54 ± 0.08 and M1450 = −27.0 ± 0.1. We also recover a z = 5.86 quasar discovered by Venemans et al., in preparation. To select our quasars, we use a new 3D colour space, combining the ATLAS optical colours with mid-infrared data from the Wide-field Infrared Survey Explorer. We use iAB − zAB colour to exclude main-sequence stars, galaxies and lower redshift quasars, W1 − W2 to exclude L dwarfs and zAB − W2 to exclude T dwarfs. A restrictive set of colour cuts returns only our three high redshift quasars and no contaminants, albeit with a sample completeness of ∼50 per cent. We discuss how our 3D colour space can be used to reject the majority of contaminants from samples of bright 5.7 < z < 6.3 quasars, replacing follow-up near-infrared photometry, whilst retaining high completeness.

Citation

Carnall, A., Shanks, T., Chehade, B., Fumagalli, M., Rauch, M., Irwin, M., …Metcalfe, N. (2015). Two bright z > 6 quasars from VST ATLAS and a new method of optical plus mid-infrared colour selection. Monthly Notices of the Royal Astronomical Society: Letters, 451(1), L16-L20. https://doi.org/10.1093/mnrasl/slv057

Journal Article Type Article
Acceptance Date Apr 16, 2015
Online Publication Date May 11, 2015
Publication Date Jul 21, 2015
Deposit Date May 28, 2015
Publicly Available Date Mar 29, 2024
Journal Monthly Notices of the Royal Astronomical Society: Letters
Electronic ISSN 1745-3933
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 451
Issue 1
Pages L16-L20
DOI https://doi.org/10.1093/mnrasl/slv057
Keywords Quasars: general, Quasars: individual: ATLAS J025.6821-33.4627, Quasars: individual: ATLAS J029.9915-36.5658.

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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