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@article{Barnett:2020:mnras/staa3808,
author = {Barnett, R and Warren, SJ and Cross, NJG and Mortlock, DJ and Fan, X and Wang, F and Hewett, PC},
doi = {mnras/staa3808},
journal = {Monthly Notices of the Royal Astronomical Society},
pages = {1663--1676},
title = {A complete search for redshift z>6.5 quasars in the VIKING survey},
url = {http://dx.doi.org/10.1093/mnras/staa3808},
volume = {501},
year = {2020}
}

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TY - JOUR
AB - We present the results of a new, deeper, and complete search forhigh-redshift $6.5<z<9.3$ quasars over 977deg$^2$ of the VISTA Kilo-DegreeInfrared Galaxy (VIKING) survey. This exploits a new list-driven datasetproviding photometry in all bands ZYJHKs, for all sources detected by VIKING in$J$. We use the Bayesian model comparison (BMC) selection method of Mortlock etal., producing a ranked list of just 21 candidates. The sources ranked 1, 2, 3and 5 are the four known $z>6.5$ quasars in this field. Additional observationsof the other 17 candidates, primarily DESI Legacy Survey photometry and ESOFORS2 spectroscopy, confirm that none is a quasar. This is the first completesample from the VIKING survey, and we provide the computed selection function.We include a detailed comparison of the BMC method against two other selectionmethods: colour cuts and minimum-$\chi^2$ SED fitting. We find that: i) BMCproduces eight times fewer false positives than colour cuts, while alsoreaching 0.3 mag. deeper, ii) the minimum-$\chi^2$ SED fitting method isextremely efficient but reaches 0.7 mag. less deep than the BMC method, andselects only one of the four known quasars. We show that BMC candidates,rejected because their photometric SEDs have high $\chi^2$ values, includebright examples of galaxies with very strong [OIII]$\lambda\lambda$4959,5007emission in the $Y$ band, identified in fainter surveys by Matsuoka et al. Thisis a potential contaminant population in Euclid searches for faint $z>7$quasars, not previously accounted for, and that requires bettercharacterisation.
AU - Barnett,R
AU - Warren,SJ
AU - Cross,NJG
AU - Mortlock,DJ
AU - Fan,X
AU - Wang,F
AU - Hewett,PC
DO - mnras/staa3808
EP - 1676
PY - 2020///
SN - 0035-8711
SP - 1663
TI - A complete search for redshift z>6.5 quasars in the VIKING survey
T2 - Monthly Notices of the Royal Astronomical Society
UR - http://dx.doi.org/10.1093/mnras/staa3808
UR - http://arxiv.org/abs/2008.10297v2
UR - https://academic.oup.com/mnras/article/501/2/1663/6030037
UR - http://hdl.handle.net/10044/1/85221
VL - 501
ER -

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