J/A+A/672/A123 Lensed QSO candidates in DESI-LS DR9 (He+, 2023)
Discovering strongly lensed quasar candidates with catalogue-based methods from
DESI Legacy Surveys.
He Z., Li N., Cao X., Li R., Zou H., Dye S.
<Astron. Astrophys. 672, A123 (2023)>
=2023A&A...672A.123H 2023A&A...672A.123H (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Gravitational lensing ; Photometry, SDSS ; Redshifts
Keywords: gravitational lensing: strong - quasars: general -
methods: data analysis - catalogues - surveys
Abstract:
The Hubble tension, revealed by a ∼5σ discrepancy between
measurements of the Hubble-Lemaitre constant from early and
local-Universe observations, is one of the most significant problems
in modern cosmology. In order to better understand the origin of this
mismatch, independent techniques to measure H0, such as strong lensing
time delays, are required. Notably, the sample size of such systems is
key to minimising statistical uncertainties and cosmic variance, which
can be improved by exploring the datasets of large-scale sky surveys
like DESI (Dark Energy Spectroscopic Instrument).
We identify possible strong lensing time-delay systems within DESI by
selecting candidate multiply imaged lensed quasars from a catalogue of
24,440,816 candidate QSOs contained in the 9th data release of the
DESI Legacy Imaging Surveys (DESI-LS).
Using a friend-of-friends-like algorithm on spatial co-ordinates, our
method generates an initial list of compact quasar groups. This list
is subsequently filtered using a measure of the similarity of colours
of a group's members and the likelihood that they are quasars. A
visual inspection finally selects candidate strong lensing systems
based on the spatial configuration of the group members.
We identify 620 new candidate multiply imaged lensed quasars (101
Grade-A, 214 Grade-B, 305 Grade-C). This number excludes 53 known
spectroscopically confirmed systems and existing candidate systems
identified in other similar catalogues. When available, these new
candidates will be further checked by combining the spectroscopic and
photometric data from DESI. The catalogues and images of the
candidates in this work are available online.
Description:
The QSO candidate catalogue (QCC) of He & Li (2022RAA....22i5021H 2022RAA....22i5021H,
https://nadc.china-vo.org/res/r101137/) contains 24440816 objects in
total. It was created from the point-like sources identified in
DESI-LS DR9 using a random forest (RF; Breiman, 2001, Machine
Learning, 45, 5) classification model. The catalogue includes the RA,
Dec, the five band magnitudes (g, r, z, W1, and W2), and the
probability of being a QSO given by the RF model.
Table 1 lists the properties given for every candidate lensed QSO
system in our H22 catalogue.
Table 2 lists the properties given for each image of each candidate
lensed QSO system.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 187 971 H22 catalog (all candidates)
table2.dat 110 1977 New candidates in detail (every images of each
candidate in H22 description)
list.dat 91 971 List of fits images
fits/* . 971 Individual fits images
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Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- IntID Internal ID that links this system to
QSO group catalogue (QGC) (internal_ID)
10- 22 F13.9 deg RAdeg Right ascension (J2000) (RA)
24- 36 F13.9 deg DEdeg Declination (J2000) (Dec)
38- 41 F4.2 --- SRF One of the scores defined in Sec. 3.2.1 (S_RF)
43- 46 F4.2 --- Scolour One of the scores defined in Sec. 3.2.1
(S_colour)
48- 59 F12.9 arcmin Sepmax Maximum image separation in arcseconds
(Sep_max)
61- 72 F12.9 arcmin Sepmin Minimum image separation in arcseconds
(Sep_min)
74- 85 F12.9 arcmin Sepmean Mean image separation in arcseconds (Sep_mean)
87 A1 --- Grade [ABC] Grades of lensed QSO candidates
(A, B, or C) (Grade)
89 A1 --- GradeLR [ABC] Grades of lensed QSO candidates
(A, B, or C) that are given independently by
the fourth author (GradebyLR)
91 I1 --- Nimg Number of images (NUMOFIMG)
93 I1 --- inKLQ Whether this candidate exists in
reference sample RLQ (in_KLQ)
95 I1 --- inD22 Whether this candidate exists in
Dawes et al., 2022 (in_D22) (1)
97 I1 --- inL22 Whether this candidate exists in
Lemon et al., 2022, MNRAS, in prep. (in_L22)
99 A1 --- GradeD22 [ABC] Grades of lensed QSO candidates
(A, B, or C) given in D22 (GradebyD22)
101-114 A14 --- Class The classification in Lemon et al., 2022,
MNRAS, in prep. (lens, NIQ, projected QSOs,
or QSO pairs) (ClassificationbyL22)
116-120 F5.3 --- q ?=- Axis ratio of SIE profile given by lens
modelling (q)
122-128 F7.3 --- phi ?=- Position angle of SIE profile
(+x-axis is zero, counterclockwise is
positive) given by lens modelling (phi)
130-134 F5.3 --- rEin ?=- Einstein radius given by lens modelling
(rein)
136-149 E14.5 --- mchi2 ?=- The chi2 that calculated by the
best-fitted lens model and observation data
(minimised_chi2)
150-162 F13.8 --- BIC ?=- The Bayesian information criterion that
is defined in Sec. 4.3. (BIC)
165-187 A23 --- Note Comments on this lensed QSO candidate (NOTE)
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Note (1): Dawes et al., 2022, Finding Multiply-Lensed and Binary Quasars in the
DESI Legacy Imaging Surveys, arXiv:2208.06356
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- IntID Internal ID that links this system to
QSO group catalogue (QGC) (internal_ID)
10- 22 F13.9 deg RAdeg Right ascension (J2000) of the centre of
this image (RA)
24- 36 F13.9 deg DEdeg Declination (J2000) of the centre of
this image (Dec)
38- 48 F11.8 mag gmag g-band magnitude of this image (g)
50- 60 F11.8 mag rmag r-band magnitude of this image (r)
62- 72 F11.8 mag zmag z-band magnitude of this image (z)
74- 84 F11.8 mag W1mag W1-band magnitude of this image (W1)
86- 96 F11.8 mag W2mag W2-band magnitude of this image (W2)
98-108 F11.9 --- z ?=- The matched redshift from eBOSS DR16
(if available) (redshift)
110 A1 --- Grade [ABC] The grades (A,B,C) of the candidate
system that this image belongs to (Grade)
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- IntID Internal ID that links this system to
QSO group catalogue (QGC)
10- 18 F9.5 deg RAdeg Right Ascension of center (J2000)
19- 27 F9.5 deg DEdeg Declination of center (J2000)
29- 32 F4.2 arcsec/pix scale Scale of the image
34- 35 I2 --- Nx Number of pixels along X-axis
37- 38 I2 --- Ny Number of pixels along Y-axis
40 I1 --- Nz Number of slices
42- 43 I2 Kibyte size Size of FITS file
45- 59 A15 --- FileName Name of FITS file, in subdirectory fits
61- 91 A31 --- Title Title of the FITS file
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Acknowledgements:
Zizhao He, zzhe(at)nao.cas.cn
(End) Patricia Vannier [CDS] 04-Apr-2023