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The VST ATLAS quasar survey I: Catalogue of photometrically selected quasar candidates

Eltvedt, Alice M; Shanks, T; Metcalfe, N; Ansarinejad, B; Barrientos, LF; Sharp, R; Malik, U; Murphy, DNA; Irwin, M; Wilson, M; Alexander, DM; Kovacs, Andras; Garcia-Bellido, Juan; Ahlen, Steven; Brooks, David; de la Macorra, Axel; Font-Ribera, Andreu; Gontcho a Gontcho, Satya; Honscheid, Klaus; Meisner, Aaron; Miquel, Ramon; Nie, Jundan; Tarlé, Gregory; Vargas-Magaña, Mariana; Zhou, Zhimin

The VST ATLAS quasar survey I: Catalogue of photometrically selected quasar candidates Thumbnail


T Shanks

B Ansarinejad

LF Barrientos

R Sharp

U Malik

DNA Murphy

M Irwin

M Wilson

Andras Kovacs

Juan Garcia-Bellido

Steven Ahlen

David Brooks

Axel de la Macorra

Andreu Font-Ribera

Satya Gontcho a Gontcho

Klaus Honscheid

Aaron Meisner

Ramon Miquel

Jundan Nie

Gregory Tarlé

Mariana Vargas-Magaña

Zhimin Zhou


We present the VST ATLAS Quasar Survey, consisting of ∼1229 000 quasar (QSO) candidates with 16 < g < 22.5 over ∼4700 deg2. The catalogue is based on VST ATLAS+NEOWISE imaging surveys and aims to reach a QSO sky density of 130 deg−2 for z < 2.2 and ∼30 deg−2 for z > 2.2. To guide our selection, we use X-ray/UV/optical/MIR data in the extended William Herschel Deep Field (WHDF) where we find a g < 22.5 broad-line QSO density of 269 ± 67 deg−2, roughly consistent with the expected ∼196 deg−2. We find that ∼25 per cent of our QSOs are morphologically classed as optically extended. Overall, we find that in these deep data, MIR, UV, and X-ray selections are ∼70–90 per cent complete while X-ray suffers less contamination than MIR and UV. MIR is however more sensitive than X-ray or UV to z > 2.2 QSOs at g < 22.5 and the SX(0.5−10keV)>1×10−14 ergs cm−2 s−1 limit of eROSITA. We adjust the selection criteria from our previous 2QDES pilot survey and prioritize VST ATLAS candidates that show both UV and MIR excess, also selecting candidates initially classified as extended. We test our selections using data from DESI (which will be released in DR1) and 2dF to estimate the efficiency and completeness, and we use ANNz2 to determine photometric redshifts. Applying over the ∼4700 deg2 ATLAS area gives us ∼917000z<2.2 QSO candidates of which 472 000 are likely to be z < 2.2 QSOs, implying a sky density of ∼100 deg−2, which our WHDF analysis suggests will rise to at least 130 deg−2 when eROSITA X-ray candidates are included. At z > 2.2, we find ∼310() 000 candidates, of which 169 000 are likely to be QSOs for a sky density of ∼36 deg−2.


Eltvedt, A. M., Shanks, T., Metcalfe, N., Ansarinejad, B., Barrientos, L., Sharp, R., …Zhou, Z. (2023). The VST ATLAS quasar survey I: Catalogue of photometrically selected quasar candidates. Monthly Notices of the Royal Astronomical Society, 521(3), 3384-3404.

Journal Article Type Article
Acceptance Date Feb 10, 2023
Online Publication Date Feb 20, 2023
Publication Date 2023-05
Deposit Date May 16, 2023
Publicly Available Date May 16, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 521
Issue 3
Pages 3384-3404


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Copyright Statement
&copy; 2023 The Author(s).<br /> Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative<br /> Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium,<br /> provided the original work is properly cited.

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