J/MNRAS/521/3384 VST ATLAS QSO survey I photometric study (Eltvedt+, 2023)
The VST ATLAS quasar survey.
I. Catalogue of photometrically selected quasar candidates.
Eltvedt A.M., Shanks T., Metcalfe N., Ansarinejad B., Barrientos L.F.,
Sharp R., Malik U., Murphy D.N.A., Irwin M., Wilson M., Alexander D.M.,
Kovacs A., Garcia-Bellido J., Ahlen S., Brooks D., De La Macorra A.,
Font-Ribera A., Gontcho A Gontcho S., Honscheid K., Meisner A., Miquel R.,
Nie J., Tarle G., Vargas-Magana M., Zhou Z.
<Mon. Not. R. Astron. Soc. 521, 3384-3404 (2023)>
=2023MNRAS.521.3384E 2023MNRAS.521.3384E (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Photometry ; Optical ; Infrared ; Redshifts ;
Combined data ; Cross identifications
Keywords: catalogues; surveys - (galaxies:) quasars: general
Abstract:
We present the VST ATLAS Quasar Survey, consisting of ∼1229000 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 erg/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 ∼917000 z<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
∼310000 candidates, of which 169000 are likely to be QSOs for a sky
density of ∼36 deg-2.
Description:
QSOs are the most luminous subset of Active Galactic Nuclei (AGNs),
which are powered by accretion onto a blackhole. we develop selection
criteria for a photometrically selected QSO catalogue based on VST
ATLAS (Shanks et al. 2015MNRAS.451.4238S 2015MNRAS.451.4238S, Cat. II/385) + unWISE neo6
(Schlafly et al. 2019ApJS..240...30S 2019ApJS..240...30S, Cat. II/363). We aim to achieve
a sky density comparable to the sky densities projected by the and
observationally confirmed by Chaussidon et al. (2022MNRAS.509.3904C 2022MNRAS.509.3904C).
We utilize methods outlined in Chehade et al. (2016MNRAS.459.1179C 2016MNRAS.459.1179C)
and develop further selection techniques by comparing our results to
X-ray QSOs from Bielby et al. (2012MNRAS.419.1315B 2012MNRAS.419.1315B) in the WHDF and
DESI DR1. This catalogue aims to be part of the spectroscopic fibre
targeting of 4MOST Cosmology Redshift Surveys combined with DES for
QSO cosmology projects. It could also be used to target eROSITA X-ray
AGN surveys and at long term to probe the nature of dark energy and
dark matter by primarily comparing gravitational lensing and redshift
space distortion analyses. See linked projects II and III.
We used VST ATLAS from DR4 version which is images ∼4700 deg2 of SGC
and 2700 deg2 of NGC. We get used of unWISE combined to DECaLS DR9
data to perform quasar selection. Also, to perform X-ray analysis, we
use the WHDF data provided by Metcalfe et al. (2001MNRAS.323..795M 2001MNRAS.323..795M) in
UBRIZHK bands for deeper magnitudes than VST ATLAS. We combined WHDF
to Chandra ACIS-I X-ray, MIR 3.6 and 4.5 m Spitzer SpIES data to
provide 0.5-10 keV X-ray fluxes and the equivalent of W1 and W2 band
magnitudes. Concerning spectroscopic redshifts surveys, we got 2QZ
catalogue which uses photometric colour cuts to select QSO targets,
therefore we test our new data completeness with 2QZ QSOs. More, we
based our selection methods to the 2QDESp one to probe fainter sources
with unWISE instead of using AllWISE. Next, to complete, we check our
VST-ATLAS photometry as well as our QSO candidate selection via
DESI/DECaLS spectroscopy/photometry. We finally test our QSO selection
using data from 2dF AAOmega spectrograph in our images fields.
As explained in section 3, we start from photometric selection methods
in multiple colour spaces by creating cuts with the help of UVX and
MIRX excess properties. Selection criteria cuts are fully described in
section 3 and 4 while completeness and efficiency tests with multiple
combined spectro/photo surveys are in section 5. As explicited in
section 6, we gave birth to final atlas qso catalogue in NGC and SGC.
Data archives are available at
(https://astro.dur.ac.uk/cea/vstatlas/qso_catalogue/). The tables
janngc.dat, jansgc.dat, marngc.dat, marsgc.dat provides used VST ATLAS
apertures photometry and unWISE W1 and W2 neo6 magnitude.
Finally, as proposed in section 7, we wish to split our three
candidate selections into two catalogues, a z < 2.2 tracer sample and
a z > 2.2 LyA sample sample using photometric redshifts for 4MOST
Cosmology Redshift Survey. Thus, we determined photometric redshifts
with annz2 software artificial neural networks and boosted
decision/regression trees to optimize the photo-z estimation which has
also been implemented as part of the analysis in DESannz2 utilizes
training based machine learning methods to derive the relationship
between photometric observables and redshift. The zph estimates are
included in tables.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
janngc.dat 365 599738 Photometry of selected VST ATLAS QSO sample in
NGC Northern Galactic Cap released in 31/01/2023
jansgc.dat 365 545713 Photometry of selected VST ATLAS QSO sample in
SGC Northern Galactic Cap released in 31/01/2023
marngc.dat 365 598862 Photometry of selected VST ATLAS QSO sample in
NGC Northern Galactic Cap released in 06/03/2023
marsgc.dat 365 629250 Photometry of selected VST ATLAS QSO sample in
SGC Northern Galactic Cap released in 06/03/2023
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See also:
J/MNRAS/520/1371 : VST ATLAS galaxy cluster I detections (Ansarinejad+, 2023)
J/MNRAS/392/19 : The 2dF-SDSS QSO survey (Croom+, 2009)
J/ApJS/225/1 : SpIES: the Spitzer IRAC Equatorial Survey (Timlin+, 2016)
J/ApJS/199/3 : The quasars MMT-BOSS pilot survey (Ross+, 2012)
J/ApJS/155/257 : NBC Quasar Candidate Catalog (Richards+, 2004)
J/AJ/154/269 : A new photo-z method for quasars in Stripe 82 (Yang+, 2017)
VII/250 : The 2dF Galaxy Redshift Survey (2dFGRS) (2dFGRS, 2003)
VII/223 : The 2dF QSO Redshift Survey. V. The 10k catalogue
(Croom+ 2001)
II/363 : The band-merged unWISE Catalog (Schlafly+, 2019)
II/350 : VLT Survey Telescope ATLAS (Shanks+, 2015)
Byte-by-byte Description of file: janngc.dat jansgc.dat marngc.dat marsgc.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 21 E21.15 deg RAdeg Right ascension of the object (J2000) (RA)
23- 42 F20.16 deg DEdeg Declination of the object (J2000) (DEC)
44- 54 A11 --- Sel The selection as Priority 1, non-UVX, or
extended that the object belongs in as explained
in section 3(selection)
56- 73 F18.15 mag umag ? VST ATLAS u-band Aperture 3 magnitude in the
AB system (u_mag)
75-101 F27.19 mag e_umag []? Error on the VST ATLAS u-band Aperture 3
magnitude (u_err)
103-120 F18.15 mag gmag VST ATLAS g-band Aperture 3 magnitude in the AB
system (g_mag)
122-143 F22.19 mag e_gmag []? Error on the VST ATLAS g-band Aperture 3
magnitude (g_err)
145-162 F18.15 mag rmag VST ATLAS r-band Aperture 3 magnitude in the AB
system (r_mag)
164-184 F21.19 mag e_rmag ? Error on the VST ATLAS r-band Aperture 3
magnitude (r_err)
186-203 F18.15 mag imag ? VST ATLAS i-band Aperture 3 magnitude in the
AB system (i_mag)
205-226 F22.19 mag e_imag []? Error on the VST ATLAS i-band Aperture 3
magnitude (i_err)
228-245 F18.15 mag zmag ? VST ATLAS z-band Aperture 3 magnitude in the
AB system (z_mag)
247-269 F23.19 mag e_zmag []? Error on the VST ATLAS z-band Aperture 3
magnitude (z_err)
271-288 F18.15 mag W1mag Neo6 W1-band magnitude in the Vega system
(W1_mag)
290-310 E21.19 mag e_W1mag Error on the neo6 W1-band magnitude (W1_err)
312-329 F18.15 mag W2mag ? Neo6 W2-band magnitude in the Vega system
(W2mag)
331-351 E21.19 mag e_W2mag ? Error on the neo6 W2-band magnitude (W2_err)
353-365 F13.11 --- zph Photometric redshift calculated using the ANNz2
algorithm (photo_z)
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History:
From electronic version of the journal
License: CC-BY-4.0
References:
Eltvedt et al. Paper I this work
Eltvedt et al. Paper II 2024MNRAS.535.2092E 2024MNRAS.535.2092E
Eltvedt et al. Paper III 2024MNRAS.535.2105E 2024MNRAS.535.2105E
(End) Luc Trabelsi [CDS] 05-Jun-2026