J/MNRAS/520/3305 ∼100 Gravitationally confirmed lensed quasars (Lemon+, 2023)
Gravitationally lensed quasars in Gaia - IV. 150 new lenses, quasar pairs,
and projected quasars.
Lemon C., Anguita T., Auger-williams M.W., Courbin F., Galan A.,
Mcmahon R., Neira F., Oguri M., Schechter P., Shajib A., Treu T.,
Agnello A., Spiniello C.
<Mon. Not. R. Astron. Soc. 520, 3305-3328 (2023)>
=2023MNRAS.520.3305L 2023MNRAS.520.3305L (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Gravitational lensing ; Galaxies ; Combined data
Photometry ; Spectroscopy ; Optical ; Positional data ;
Redshifts ; Photometry, classification ; Morphology
Keywords: gravitational lensing: strong - methods: observational -
quasars: general
Abstract:
We report the spectroscopic follow-up of 175 lensed quasar candidates
selected using Gaia Data Release 2 observations following Paper III of
this series. Systems include 86 confirmed lensed quasars and a further
17 likely lensed quasars based on imaging and/or similar spectra. We
also confirm 11 projected quasar pairs and 11 physical quasar pairs,
while 25 systems are left as unclassified quasar pairs - pairs of
quasars at the same redshift, which could be either distinct quasars
or potential lensed quasars. Especially interesting objects include
eight quadruply imaged quasars of which two have BAL sources, an
apparent triple, and a doubly lensed LoBaL quasar. The source
redshifts and image separations of these new lenses range between
0.65-3.59 and 0.78-6.23 arcsec, respectively. We compare the known
population of lensed quasars to an updated mock catalogue at image
separations between 1 and 4 arcsec, showing a very good match at z <
1.5. At z > 1.5, only 47 per cent of the predicted number are known,
with 56 per cent of these missing lenses at image separations below
1.5 arcsec. The missing higher redshift, small-separation systems will
have fainter lensing galaxies, and are partially explained by the
unclassified quasar pairs and likely lenses presented in this work,
which require deeper imaging. Of the 11 new reported projected quasar
pairs, 5 have impact parameters below 10 kpc, almost tripling the
number of such systems, which can probe the innermost regions of
quasar host galaxies through absorption studies. We also report four
new lensed galaxies discovered through our searches, with source
redshifts ranging from 0.62 to 2.79.
Description:
Recent optical to near-infrared surveys now provide an efficient way
to select high-confidence quasar candidates across the whole sky , and
have the resolution and depth to identify whether such systems are
lensed, i.e. whether there are multiple images and a lensing galaxy
present. However, lensed quasars are particularly rar. The all-sky
space-based catalogues from Gaia offer a particularly effective way of
removing these contaminants. In the previous papers of this series, we
have shown that combining the Gaia catalogue detections and parameters
with WISE and ground-based optical imaging can efficiently remove the
common contaminants of lensed quasar searches. In this paper, we
continue our spectroscopic follow-up campaign of lensed quasar
candidates selected with the techniques developed in these papers (see
introduction section).
We focus on untargetted systems in previously covered sky, due to lack
of spectroscopic follow-up time. Two searches begin from a catalogue
of quasars and quasar candidates. For these searches we used the
Milliquas catalogue (likely quasar candidates based on X-ray, radio,
and optical and infrared colour selection) and colours catalgue from
WISE in which we detect multiple Gaia sources. Concerning, spectrocopy
follow-up, we use spectrographs from three telescopes Herschel, NOT
and NTT. We explained general reduction procedure to resolve and
confirmed lensed quasars in section 3.1. Next, we investigated Gaia
detections (fit the pixels with a combination of analytic profiles and
then identify if a lensing galaxy is present between two bright quasar
PSFs as exposed in section 3.2), with science images from grizY
Pan-STARRS, DESI, VizieR/NED and HST multibands. Astrometric,
photometry and classification/morphology results as well as redshift
are provided in table1.dat for our 179 observed targets.
(See section 4 for additional notes on individual systems and section
5 for compare several properties of the new lenses to previously known
lenses in order to elucidate possible biases in our selection methods
and/or those of previous discovery methods, mostly taken from Lemon et
al. 2019MNRAS.483.4242L 2019MNRAS.483.4242L, Paper III).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 137 179 Observed targets informations and results
based on spectroscopy and photometry imaging
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See also:
J/MNRAS/486/4987 : Gravitationally lensed quasars in Pan-STARRS1 (Rusu+, 2019)
J/MNRAS/452/2553 : Sample of foreground-background quasar pairs (Johnson+,2015)
J/A+A/657/A113 : QSO J1721+8842 spectra (Lemon+, 2022)
J/A+A/649/A3 : Gaia Early Data Release 3 photometric passbands
(Riello+, 2021)
J/A+A/480/611 : XMM-Newton Slew Survey catalogue, XMMSL1 (Saxton+, 2008)
J/ApJ/925/162 : VODKA: HST discovers double SDSS-Gaia quasars (Chen+, 2022)
J/ApJ/921/42 : Gaia GraL. VI. Quadruply imaged lensed QSOs (Stern+, 2021)
J/ApJ/863/144 : The ELQS in SDSS footprint. II. North Gal. Cap
(Schindler+, 2018)
J/ApJ/776/136 : QPQ VI. HI absorption of z∼2 quasars (Prochaska+, 2013)
J/ApJ/773/14 : BOSS: quasar luminosity function (Ross+, 2013)
J/ApJ/743/156 : NEOWISE observations of NEOs: preliminary results
(Mainzer+, 2011)
J/ApJ/719/1672 : SDSS binary quasars at high redshift. I. (Hennawi+, 2010)
J/ApJ/716/521 : 31GHz sky survey with the SZA (Muchovej+, 2010)
J/ApJ/651/61 : Optically thick absorbers near luminous quasars
(Hennawi+, 2006)
J/ApJS/255/30 : VLASS QL Ep.1 Catalog, CIRADA version (Gordon+, 2021)
J/ApJS/224/40 : Catalog of Chandra ACIS point like sources (Wang+, 2016)
J/ApJS/213/35 : SHELS: complete galaxy redshift survey for R≤20.6
(Geller+, 2014)
J/AJ/135/496 : SDSS quasar lens search. II. (Inada+, 2008)
J/AJ/132/999 : SDSS quasar lens search (Oguri+, 2006)
IX/59 : XMM-Newton Serendipitous Source Catalogue 4XMM-DR9
(Webb+, 2020)
VIII/100 : GaLactic and Extragalactic All-sky MWA survey
(Hurley-Walker+, 2016)
VIII/72 : CLASS survey of radio sources (Myers+, 2003)
VIII/70 : Sydney University Molonglo Sky Survey (SUMSS) (Mauch+ 2003)
VII/273 : The Half Million Quasars (HMQ) catalogue (Flesch, 2015)
VII/241 : The 2dF QSO Redshift Survey (Croom+ 2004)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+,2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Name of the observed target (Name)
12- 20 F9.5 deg RAdeg Right ascension (J2000) (R.A.)
22- 30 F9.5 deg DEdeg Declination (J2000) (Dec.)
32- 36 A5 --- Obs Selected observations with multiple Gaia
detections (Selection) (1)
38- 42 F5.2 mag G1mag ? First G-band mean magnitude in Vega system
(GaiaG1)
44- 48 F5.2 mag G2mag ? Second G-band mean magnitude in Vega system
(GaiaG2)
50- 54 F5.2 mag G3mag ? Third G-band mean magnitude in Vega system
(GaiaG3)
56- 60 F5.2 mag G4mag ? Fourth G-band mean magnitude in Vega system
(GaiaG4)
62- 65 F4.2 arcsec Sep Angular separation (Sep.) (2)
67- 70 F4.2 --- sigPM1 ? First PMSIG of the Gaia detections (PMSIG1)
(3)
72- 75 F4.2 --- sigPM2 ? Second PMSIG of the Gaia detections (PMSIG2)
(3)
77- 80 F4.2 --- sigPM3 ? Third PMSIG of the Gaia detections (PMSIG3)
(3)
82 A1 --- n_Run Note on observing runs (4)
84- 92 A9 --- Run Observing run name (Run) (5)
94-110 A17 --- Class System classifications (Classification) (6)
112-117 F6.4 --- z ? First measured redshift of the system (z)
119-120 A2 --- f_z Flag for unsure redshift values
122-128 A7 --- n_z2 Note on z2 to indicate redshift of lens, qso,
or galaxy, z2 is logically smaller than z1 for
lensed quasar systems
130-135 F6.4 --- z2 ? Second redshift in case of multiple objects
in the system
137 A1 --- f_z2 Flag for unsure redshift values
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Note (1): Catalogue selections with multiple Gaia detections are as follows:
WD = Double Gaia source detections in WISE colour images,
142 occurences in our sample
WT = Triple Gaia source detections in WISE colour images,
5 occurences in our sample
WQ = Quartet Gaia source detections in WISE colour images,
1 occurence in our sample
MD = Double Gaia source detections in Milliquas images,
93 occurences in our sample
MT = Triple Gaia source detections in Milliquas images,
2 occurences in our sample
GP = Gaia singlet offset from a galaxy as explained in section 2.3
Gaia detections offset from LRGs,
26 occurences in our sample
Note (2): Which is the largest of the Gaia separations if more than two
Gaia DR2 detections are associated to the system, or based on
pixel modelling.
Note (3): Proper motion significance of Gaia detections associated to the system
as defined in Lemon et al. (2019MNRAS.483.4242L 2019MNRAS.483.4242L).
Note (4): These systems were observed on separated observing runs: lensed galaxy
J0500-5534 see subsection 4.7.2, lensed galaxy J0920+4521 see
subsection 4.7.3, lensed galaxy J1102+3421 see subsection 4.7.4.
Note (5): Observing runs are as follows:
WHT = William Herschel telescope with the Intermediate-dispersion
Spectrograph and Imaging System ISIS, see section 3.1.1,
57 occurences in our sample
NTT1 = First run of the New technology telescope with ESO Faint
Object Spectrograph and Camera version 2 runs, see
section 3.1.3, 26 occurences in our sample
NTT2 = Second run of the New technology telescope with ESO Faint
Object Spectrograph and Camera version 2 runs, see
section 3.1.3, 29 occurences in our sample
NTT3 = Third run of the New technology telescope with ESO Faint
Object Spectrograph and Camera version 2 runs,
see section 3.1.3, 13 occurences in our sample
NTT4 = Fourth run of the New technology telescope with ESO Faint
Object Spectrograph and Camera version 2 runs,
see section 3.1.3, 12 occurences in our sample
NOT = Nordic optical telescope with the Alhambra Faint Object
Spectrograph and Camera ALFOSC, see section 3.1.2,
43 occurences in our sample
Mag = Follow-up spectroscopy with FIRE on the 6.5-m Baade Magellan
telescope shows clearly resolved narrow emission lines
of a z = 0.620 galaxy as explained in subsection 4.7.2
J0500-5534, 1 occurence in our sample
Long-slit spectroscopy was obtained for 175 candidates at three
telescopes, with instrument setups. Slit position angles were
calculated using Gaia astrometry for systems with multiple
detections, otherwise they were measured using fitted image
positions in Pan-STARRS or DES data. Typical exposure times were
600 to 900s, depending on brightness, and seeing was generally
between 0.7 and 1.1 arcsec (see section 3).
Note (6): As detailed in section 3.3, we broadly classify the systems into the
following categories as follows:
lens = definite lensed quasars, 78 occurences in our sample
lens (?) = likely lensed quasars (based on the subjective opinion
and experience of the authors), 1 occurences in our
sample
lensed gal. = Spectroscopically confirmed lensed galaxies,
4 occurences in our sample
UQP = unclassified quasar pairs (systems in which two quasars
are spectroscopically resolved and are at the same
redshift however no convincing lensing galaxy is seen
but also for which there is no clear evidence for
them being physically distinct quasars),
38 occurences in our sample
UQP (?) = likely UQP, 1 occurence in our sample
QSO pair = binary quasars (see section 5.2, distinct quasar
pairs at very similar redshifts.), 11 occurences in
our sample
proj. QSOs = projected quasars (see section 5.3, new projected
quasar pairs, with angular separations ranging
from 0.98 to 4.64 arcsec, and physical impact
parameters from 6.2 to 34.3 kpc),
11 occurences in our sample
Contaminant systems (definitely not lenses) as ["stars", "quad",
"galaxy + stars", "galaxy + star", "galaxy", "galaxies",
"QSO + star", "QSO + star(?)", "QSO + other", "Galaxy + QSO",
"Galaxy + QSO"]. We note that our use of unclassified quasar pairs
is akin to Nearly Identical Quasars (NIQs) which has been used in
recent literature (e.g. Anguita et al. 2018MNRAS.480.5017A 2018MNRAS.480.5017A ),
however the change is simply to include those systems which have
low signal-to-noise data and could readily be classified as a
likely lensed quasar or binary quasar given deeper spectra.
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History:
From electronic version of the journal
References:
Lemon et al., Paper I 2017MNRAS.472.5023L 2017MNRAS.472.5023L
Lemon et al., Paper II 2018MNRAS.479.5060L 2018MNRAS.479.5060L
Lemon et al., Paper III 2019MNRAS.483.4242L 2019MNRAS.483.4242L
Lemon et al., Paper IV This work
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Luc Trabelsi [CDS] 25-Mar-2026