J/ApJ/894/78 Strong gravitational lenses from DECaLS (Huang+, 2020)
Finding strong gravitational lenses in the DESI DECam Legacy Survey.
Huang X., Storfer C., Ravi V., Pilon A., Domingo M., Schlegel D.J.,
Bailey S., Dey A., Gupta R.R., Herrera D., Juneau S., Landriau M., Lang D.,
Meisner A., Moustakas J., Myers A.D., Schlafly E.F., Valdes F., Weaver B.A.,
Yang J., Yeche C.
<Astrophys. J., 894, 78 (2020)>
=2020ApJ...894...78H 2020ApJ...894...78H
ADC_Keywords: Gravitational lensing; Photometry, ugriz; Redshifts; Surveys;
Galaxies, photometry
Keywords: Strong gravitational lensing ; High-redshift galaxies ; Galaxies ;
Galaxy clusters ; Galaxy groups
Abstract:
We perform a semi-automated search for strong gravitational lensing
systems in the 9000 deg2 Dark Energy Camera Legacy Survey (DECaLS),
part of the Dark Energy Spectroscopic Instrument Legacy Imaging
Surveys. The combination of the depth and breadth of these surveys are
unparalleled at this time, making them particularly suitable for
discovering new strong gravitational lensing systems. We adopt the
deep residual neural network architecture developed by
Lanusse+ (2018MNRAS.473.3895L 2018MNRAS.473.3895L) for the purpose of finding strong
lenses in photometric surveys. We compile a training sample that
consists of known lensing systems in the Legacy Surveys and the Dark
Energy Survey as well as non-lenses in the footprint of DECaLS. In
this paper we show the results of applying our trained neural network
to the cutout images centered on galaxies typed as ellipticals in
DECaLS. The images that receive the highest scores (probabilities) are
visually inspected and ranked. Here we present 335 candidate strong
lensing systems, identified for the first time.
Description:
The details of the Dark Energy Spectroscopic Instrument (DESI) Legacy
Imaging Surveys are described in Dey+ (2019AJ....157..168D 2019AJ....157..168D). Here we
present a brief summary. The Legacy Surveys consist of three projects:
the Dark Energy Camera Legacy Survey (DECaLS), observed by the Dark
Energy Camera (DECam) on the 4m Blanco telescope at the Cerro Tololo
Inter-American Observatory; the Beijing-Arizona Sky Survey (BASS), by
the 90Prime camera on the Bok 2.3m telescope owned and operated by the
University of Arizona located on Kitt Peak; and the Mayall z-band
Legacy Survey (MzLS), by the Mosaic3 camera on the 4m Mayall telescope
at Kitt Peak National Observatory.
For DECaLS, the delivered image quality has a FWHM of approximately
1.29, 1.18, 1.11" for g, r, and z bands respectively. We choose here
to focus on DECaLS due to its better gr seeing than BASS.
See Section 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 63 60 *Grade A candidates
table2.dat 63 106 *Grade B candidates
table3.dat 63 176 *Grade C candidates
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Note on table1.dat and table2.dat and table3.dat: Grade as follows:
A = We have a high level of confidence of these candidates. Many of them have
one or more prominent arcs, usually blue. The rest have one or more
clear arclets, sometimes arranged in counter-image configurations with
similar colors (again, typically blue). However, there are clear cases
with red arcs.
B = They have similar characteristics as the Grade As. For the cutout images
where there appear to be giant arcs they tend to be fainter than those
for the Grade As. Likewise, the putative arclets tend to be smaller
and/or fainter, or isolated (without counter images).
C = They generally have features that are even fainter and/or smaller than
what is typical for the Grade B candidates, but that are nevertheless
suggestive of lensed arclets. They are usually without counter images,
except for a few cases. In almost all cases, if these are indeed
lensing systems, the deflection angles are comparable to or only
slightly larger than the seeing.
See Section 4.
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See also:
II/284 : COSMOS Multi-Wavelength Photometry Catalog (Capak+, 2007)
II/344 : KiDS-ESO-DR2 multi-band source catalog (de Jong+, 2015)
J/ApJ/749/38 : CFHTLS-SL2S-ARCS strong lens candidates (More+, 2012)
J/ApJ/755/31 : Compilation of 122 strong gravitational lenses (Cao+, 2012)
J/MNRAS/465/4914 : R-band light curves of HE 0435-1223 (Bonvin+, 2017)
J/ApJ/834/210 : Spectroscopy of strong lensing clusters (Carrasco+, 2017)
J/ApJS/232/15 : Candidate strong lens systems from DES obs. (Diehl+, 2017)
J/ApJ/856/68 : COSMOS lens candidates with LensFlow (Pourrahmani+, 2018)
J/ApJ/857/144 : Tidal features from RESOLVE & DECaLS (Hood+, 2018)
J/ApJS/247/12 : Strong lens models for 37 clusters from SGAS (Sharon+, 2020)
J/MNRAS/500/859 : Ridges in the Dark Energy Survey (Moews+, 2021)
Byte-by-byte Description of file: table[123].dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name Name of the source (DESI-DDD.dddd+DD.dddd; J2000)
23- 26 A4 --- Type Source type (1)
28- 32 F5.2 --- gmag [17.44/29.52] CTIO/DECam g-band magnitude
34- 38 F5.2 --- rmag [15.82/23.38] CTIO/DECam r-band magnitude
40- 44 F5.2 --- zmag [14.95/20.87] CTIO/DECam z-band magnitude
46- 50 F5.3 --- Prob [0.45/1] Probability (>0.9 = best lens candidates;
see Section 4.2)
52- 57 F6.4 --- z [0.13/0.91]? Redshift from Survey;
redshift uncertainties <3.7x10-4 for
Grades A and B and <3.9x10-4 for Grade C
59- 63 A5 --- Survey Survey identifier (BOSS, eBOSS or SDSS) (2)
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Note (1): After source detection, the point source ("PSF") and spatially
extended ("REX," round exponential galaxy) models are computed for
every source and the better of these two is used when deciding whether
to keep the source. The spatially extended sources (REX) are further
classified if χ2 is improved by 9 by treating it as a
deVaucouleurs (DEV), an exponential (EXP) profile, or a composite of
DEV+exponential (COMP).
The categories of DEV and COMP indicate the classification of
elliptical galaxies. See Section 2.
Note (2): We checked our candidate list against the spectroscopic database
from SDSS I and II (York+ 2000AJ....120.1579Y 2000AJ....120.1579Y),
SDSS III/BOSS (Eisenstein+ 2011AJ....142...72E 2011AJ....142...72E), and
SDSS IV/eBOSS (Blanton+ 2017AJ....154...28B 2017AJ....154...28B) and found 121 matches,
which is slightly greater than one third of all candidates.
See Section 4.1.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 15-Sep-2021