J/A+A/592/A75 New lens candidates in CFHTLS (Paraficz+, 2016)
The PCA Lens-Finder: application to CFHTLS.
Paraficz D., Courbin F., Tramacere A., Joseph R., Metcalf R.B.,
Kneib J.-P., Dubath P., Droz D., Filleul F., Ringeisen D., Schafer C.
<Astron. Astrophys., 592, A75 (2016)>
=2016A&A...592A..75P 2016A&A...592A..75P (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Gravitational lensing ; Galaxies, photometry
Keywords: gravitational lensing: strong - galaxies: general - surveys
Abstract:
We present the results of a new search for galaxy-scale strong lensing
systems in CFHTLS Wide. Our lens-finding technique involves a
preselection of potential lens galaxies, applying simple cuts in size
and magnitude. We then perform a Principal Component Analysis of the
galaxy images, ensuring a clean removal of the light profile. Lensed
features are searched for in the residual images using the clustering
topometric algorithm DBSCAN. We find 1098 lens candidates that we
inspect visually, leading to a cleaned sample of 109 new lens
candidates. Using realistic image simulations we estimate the
completeness of our sample and show that it is independent of source
surface brightness, Einstein ring size (image separation) or lens
redshift. We compare the properties of our sample to previous lens
searches in CFHTLS. Including the present search, the total number of
lenses found in CFHTLS amounts to 678, which corresponds to ∼4 lenses
per square degree down to i(AB)=24.8. This is equivalent to ∼60.000
lenses in total in a survey as wide as Euclid, but at the CFHTLS
resolution and depth.
Description:
Our main goal in this work is to complement and extend current samples
of galaxy-scale strong lens candidates, starting with the public
imaging data from the CFHTLS. To do so, we use the new technique
proposed by Joseph et al. (2014A&A...566A..63J 2014A&A...566A..63J).
In this paper, we use the T0007 (Cat. II/317) final release of the
CFHTLS with improved flat-fielding and photometric calibration
techniques developed by the Supernova Legacy Survey (SNLS) team in
collaboration with the CFHT.
We rank each object in one of the following categories:
- A : an almost definite lens with a striking image configuration
that is typical for lensing
- B : probable lens, but the candidate would need follow-up with
spectroscopy or more imaging
- C : possible lens, but with low probability of being confirmed,
either because of low signal-to-noise (S/N) or because the
potential lensed images are single or consist of short arcs
that could still be compatible with edge-on galaxies or
chain galaxies
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 85 109 *Grade-A and grade-B new lens candidates in CFHTLS
tablea1.dat 21 274 Ring-like galaxies
tablea2.dat 21 183 *Our grade-C candidates in CFHTLS
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Note on table1.dat:
Grade A : an almost definite lens with a striking image configuration
that is typical for lensing
Grade B : probable lens, but the candidate would need follow-up with
spectroscopy or more imaging
Note on tablea2.dat:
Grade C : possible lens, but with low probability of being confirmed, either
because of low signal-to-noise (S/N) or because the potential lensed images
are single or consist of short arcs that could still be compatible with
edge-on galaxies or chain galaxies
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See also:
II/317 : The CFHTLS Survey (T0007 release) (Hudelot+ 2012)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/109] Sequential number, within the table
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 21 F8.4 deg DEdeg Declination (J2000)
23- 27 F5.3 --- z Photometric redshift (1)
28 A1 --- --- [+]
29- 33 F5.3 --- B_z Upper value of redshift interval
34 A1 --- --- [-]
35- 39 F5.3 --- b_z Lower value of redshift interval
41- 44 F4.2 pix Reff Effective radius (1)
46- 50 F5.2 mag gmag SDSS g magnitude (1)
52- 55 F4.2 mag e_gmag rms uncertainty on gmag
57- 61 F5.2 mag rmag SDSS r magnitude (1)
63- 66 F4.2 mag e_rmag rms uncertainty on rmag
68- 72 F5.2 mag imag SDSS i magnitude (1)
74- 77 F4.2 mag e_imag rms uncertainty on imag
79- 83 F5.2 pix RE Einstein radius
85 A1 --- Qual [AB] Quality flag
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Note (1): The photometric redshifts z, the effective radius Reff and the
magnitudes are the ones provided by Coupon et al. (2009A&A...500..981C 2009A&A...500..981C).
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Byte-by-byte Description of file: tablea1.dat tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/274]Sequential number within the table
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 21 F8.4 deg DEdeg Declination (J2000)
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History:
* 05-Dec-2016: From electronic version of the journal
* 18-Oct-2017: complete table1 added
(End) Patricia Vannier [CDS] 10-Nov-2016