J/A+A/622/A165 Gaia GraL. III. New lensed systems (Delchambre+, 2019)
Gaia GraL: Gaia DR2 Gravitational Lens Systems.
III. A systematic blind search for new lensed systems.
Delchambre L., Krone-Martins A., Wertz O., Ducourant C., Galluccio L.,
Kluter J., Mignard F., Teixeira R., Djorgovski S.G., Stern D.,
Graham M.J., Surdej J., Bastian U., Wambsganss J., Le Campion J.-F.,
Slezak E.
<Astron. Astrophys. 622, A165 (2019)>
=2019A&A...622A.165D 2019A&A...622A.165D (SIMBAD/NED BibCode)
ADC_Keywords: Gravitational lensing ; Positional data
Keywords: gravitational lensing: strong - methods: data analysis - catalogues
Abstract:
The Gaia GraL catalogue of clusters is composed of 2,129,659 clusters
consisting of three or four stationary sources from Gaia DR2. Each
cluster is assigned a discriminant value, called the extremely
randomized trees probability, that reflects its ability to be matched
to the image positions and relative magnitudes produced through
simulations of gravitational lens systems.
Description:
The Gaia GraL catalogue of clusters consist of 2,058,962 clusters with
three components and 70,697 clusters with four components. Each of
these clusters satisfied the following conditions:
i) Clusters are composed of three or four images in order to provide a
sufficient number of constraints for identifying gravitational lens
candidates.
ii) Their constituent images have negligible parallaxes, plx, and
proper motions, (pmra', pmdec) where pmra' = pmra * cos(dec).
Specifically, we required that plx-3*e_plx<4mas and
abs(pm)-3*e_pm<4mas (where e_X is the mean error on X and pm
stands for pmra' and pmdec).
iii) The maximal angular separation between any pair of images is
below or equal to 6 arcsec.
iv) The absolute difference in G magnitude between components is lower
or equal to 4mag.
v) Clusters are located in regions with a mean field density lower
than 60000 objects/deg2. The mean density of objects is computed
within a radius of 30 arcsec around each cluster.
Based on a supervised learning method, called extremely randomized
trees (ERT), each cluster is assigned a discriminant value: the ERT
probability. This ERT probability reflects the ability of the clusters
to be matched to the image positions and relative magnitudes produced
from simulations of lens systems based on a non-singular isothermal
ellipsoid lens model (Kormann+, 1994) in the presence of an external
shear (Kovner, 1987). These probabilities do not constitute
probabilities in a mathematical sense, although they can be translated
into expected ratios of identification of gravitational lenses (the
true positive rate, TPR) and to expected ratios of misclassification
of groups of stars as gravitational lenses (the false positive rate,
FPR) through the use of an appropriate cross-validation procedure (see
the description of the roc*.dat files).
As we expect some of the lensed images to be missing from Gaia DR2,
all combinations of three and four images were considered fo building
the ERT. The resulting ERT models wil be referred to as ABCD, ABC,
ABD, ACD and BCD where A, B, C, D identify the images we used for
building the corresponding ERT model, assuming these are sorted in
ascending order of G magnitude.
Finally, the receiver operating characteristics (ROC) curves from
files roc.dat, rocabc.dat, rocabd.dat, rocacd.dat, and rocbcd.dat are
obtained by computing the TPR and FPR that are associated with all ERT
probabilities coming from the corresponding ERT model based on a test
set and a validation set of observations. The test set of observations
(TS) is composed of 5*107 gravitational lenses simulated from a
non-singular isothermal ellipsoid lens model in the presence of an
external shear and of the same number of simulated contaminants where
the relative image positions and fluxes are randomly drawn from a
uniform distribution. The validation set of observations (VS) is
composed of 12 known lensed systems having four detections in Gaia DR2
(2MASSJ11344050-2103230, J1606-2333, WGD2038-4008, HE0435-1223,
SDSS1004+4112, PG1115+080, B1422+231, 2MASXJ01471020+4630433,
2MASSJ13102005-1714579, J1721+8842, WFI2033-4723 and RXJ1131-1231) and
of 1e6 clusters we randomly extracted from Gaia DR2 with a size
smaller than 30 arcsec and a maximal absolute difference in G
magnitude between their constituent images <4mag.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 205 6459674 Catalogue of clusters of Gaia DR2 sources
roc.dat 40 101 VS- and TS-ROC curves of ERT model ABCD
rocabc.dat 40 101 VS- and TS-ROC curves of ERT model ABC
rocabd.dat 40 101 VS- and TS-ROC curves of ERT model ABD
rocacd.dat 40 101 VS- and TS-ROC curves of ERT model ACD
rocbcd.dat 40 101 VS- and TS-ROC curves of ERT model BCD
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/6128/A56 : Gaia GraL. II. Known multiply imaged quasars (Ducourant+ 2018)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 I7 --- Seq [1/6459674] Unique identifier of the row in
the catalogue (1)
9- 27 A19 --- Name Unique identifier of the cluster (2)
32 I1 --- Nimg [3,4] The number of images constituting the
cluster
34- 40 F7.5 arcsec Size ]0,6] The maximal angular separation between
any two images of the cluster
42- 67 A26 --- Known ? Identifier in the list of known and
candidate GL (3)
71- 75 I5 ct/deg2 Density ]0,6e4[ The mean density of objects
surrounding the cluster (4)
77- 84 F8.6 mag dmag [0,4] The maximal absolute difference in the G
magnitude, between the images of the cluster
86- 93 F8.6 mag dcolor ? The maximal absolute difference in colour
between the images of the cluster (5)
100 I1 --- Ncolor [0,4] The number of images having colour
information that are used in the computation
of dcolor
102-105 F4.2 --- P [0,1] ERT probability associated with this
cluster (7) (6)
107-110 F4.2 --- PABC [0,1]? ERT probability computed based on the
ABC model. Empty if nimg=4. (7)
112-115 F4.2 --- PABD [0,1]? ERT probability computed based on the
ABD model. Empty if nimg=4. (7)
117-120 F4.2 --- PACD [0,1]? ERT probability computed based on the
ACD model. Empty if nimg=4. (7)
122-125 F4.2 --- PBCD [0,1]? ERT probability computed based on the
BCD model. Empty if nimg=4. (7)
127-145 I19 --- SourceId Unique source identifier from Gaia DR2
147-160 F14.10 deg RAdeg Right ascension of the source in ICRS
coordinates at epoch 2015.5 from Gaia DR2
162-175 F14.10 deg DEdeg Declination of the source in ICRS coordinates
at epoch 2015.5 from Gaia DR2
177-185 F9.6 mag Gmag G-band mean magnitude from Gaia DR2
187-195 F9.6 mag BPmag ? Integrated BP mean magnitude from Gaia DR2
Empty if no BP magnitude is available
197-205 F9.6 mag RPmag ? Integrated RP mean magnitude from Gaia DR2
Empty if no RP magnitude is available
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Note (1): Each combination of the name and of the SourceId is always associated
with a unique row.
Note (2): This identifier is based on the mean position of the images of the
cluster taken in sexagesimal coordinates, HHMMSSs+DDMMSSsss
Note (3): from (Ducourant+, 2018, Cat. J/A+A/618/A56).
Empty if this cluster is not recognized as a known GL or candidate
Note (4): estimated by counting the Gaia DR2 objects falling in a 30 arcsec
radius around one of its constituent members.
Note (5): Empty if less than two images comes along with color informations
(i.e. BPmag or RPmag is empty).
Note (6): If nimg=4, then this parameter corresponds to the ERT probabilities
computed based on the ABCD model.
If nimg=3, then this field is taken as the maximum of PABC, PABD, PACD
and PBCD.
Note (7): The expected ratio of identification of gravitational lenses
(i.e. true positive rate) and expected ratio of misclassification of groups of
stars as gravitational lenses (i.e. false positive rate) that are associated
with each of the ERT probabilities PABC, PABD, PACD, PBCD if nimg=3 and
P if nimg=4 are respectively given by the receiver operating characteristics
(ROC) curves from files rocABC.dat, rocABD.dat, rocACD.dat, rocBCD.dat and
roc.dat .
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Byte-by-byte Description of file: roc*.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.2 --- T [0,1] Threshold on the ERT probability, p (1)
6- 13 F8.6 --- TStpr [0,1] True positive rate computed on the test
set of observations
15- 22 F8.6 --- TSfpr [0,1] False positive rate computed on the test
set of observations
24- 31 F8.6 --- VStpr [0,1] True positive rate computed on the
validation set of observations
33- 40 F8.6 --- VSfpr [0,1] False positive rate computed on the
validation set of observations
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Note (1): Observations having p>T are classified as gravitational lenses during
the computation of the associated true and false positive rates.
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Acknowledgements:
Ludovic Delchambre, ldelchambre(at)uliege.be
References:
Krone-Martins et al. Paper I 2018A&A...616L..11K 2018A&A...616L..11K
Ducourant et al. Paper II 2018A&A...618A..56D 2018A&A...618A..56D Cat. J/A+A/618/A56
Delchambre et al. Paper III 2019A&A...622A.165D 2019A&A...622A.165D This catalogue
Wertz et al. Paper IV 2019A&A...628A..17W 2019A&A...628A..17W
Krone-Martins et al. Paper V 2019arXiv191208977K 2019arXiv191208977K
Stern et al. Paper VI 2021ApJ...921...42S 2021ApJ...921...42S Cat. J/ApJ/921/42
Connor et al. Paper VII 2022ApJ...927...45C 2022ApJ...927...45C
(End) Patricia Vannier [CDS] 16-Jan-2019