J/ApJ/785/144 SL2S galaxy-scale sample of lens candidates (Gavazzi+, 2014)
RINGFINDER: automated detection of galaxy-scale gravitational lenses
in ground-based multi-filter imaging data.
Gavazzi R., Marshall P.J., Treu T., Sonnenfeld A.
<Astrophys. J., 785, 144 (2014)>
=2014ApJ...785..144G 2014ApJ...785..144G (SIMBAD/NED BibCode)
ADC_Keywords: Galaxy catalogs ; Gravitational lensing ; Photometry, SDSS ;
Redshifts
Keywords: methods: data analysis - methods: statistical -
galaxies: elliptical and lenticular, cD -
gravitational lensing: strong - surveys - techniques: miscellaneous
Abstract:
We present RINGFINDER, a tool for finding galaxy-scale strong
gravitational lenses in multi-band imaging data. By construction, the
method is sensitive to configurations involving a massive foreground
ETG and a faint, background, blue source. RINGFINDER detects the
presence of blue residuals embedded in an otherwise smooth red light
distribution by difference imaging in two bands. The method is
automated for efficient application to current and future surveys,
having originally been designed for the 150 deg2
Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We describe
each of the steps of RINGFINDER. We then carry out extensive
simulations to assess completeness and purity. For sources with
magnification µ>4, RINGFINDER reaches 42% (25%) completeness and
29% (86%) purity before (after) visual inspection. The completeness of
RINGFINDER is substantially improved in the particular range of
Einstein radii 0.8"≤REin≤2.0" and lensed images brighter
than g=22.5, where it can be as high as ∼70%. RINGFINDER does not
introduce any significant bias in the source or deflector population.
We conclude by presenting the final catalog of RINGFINDER CFHTLS
galaxy-scale strong lens candidates. Additional information obtained
with Hubble Space Telescope and Keck adaptive optics high-resolution
imaging, and with Keck and Very Large Telescope spectroscopy, is used
to assess the validity of our classification and measure the redshift
of the foreground and the background objects. From an initial sample
of 640000 ETGs, RINGFINDER returns 2500 candidates, which we further
reduce by visual inspection to 330 candidates. We confirm 33 new
gravitational lenses from the main sample of candidates, plus an
additional 16 systems taken from earlier versions of RINGFINDER. First
applications are presented in the Strong Lensing Legacy Survey
galaxy-scale lens sample paper series.
Description:
The CFHTLS5 is a major photometric survey of more than 450 nights over
5 yr (started on 2003 June 1) using the MegaCam wide-field imager,
which covers ∼1 deg2 on the sky, with a pixel size of 0.186". The
CFHTLS has two components aimed at extragalactic studies: a Deep
component consisting of four pencil-beam fields of 1 deg2 and a wide
component consisting of four mosaics covering 150 deg2 in total. Both
surveys are imaged through five broadband filters. The data are
pre-reduced at CFHT with the Elixir pipeline
(http://www.cfht.hawaii.edu/Instruments/Elixir/), which removes the
instrumental artifacts in individual exposures. The CFHTLS images are
then astrometrically calibrated, photometrically inter-calibrated,
resampled and stacked by the Terapix group at the Institut d'Astrophysique
de Paris, and finally archived at the Canadian Astronomy Data Centre.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 59 330 The SL2S galaxy-scale main sample of lens
candidates in the CFHTLS-Wide
table3.dat 59 71 Additional SL2S lens candidates
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See also:
J/ApJ/749/38 : CFHTLS-SL2S-ARCS strong lens candidates (More+, 2012)
J/ApJ/777/97 : SL2S galaxy-scale lens sample. III. (Sonnenfeld+, 2013)
J/ApJ/833/194 : Group of galaxies in gravitational lens fields (Wilson+, 2016)
Byte-by-byte Description of file: table1.dat table3.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name SL2S catalog identifier (SL2S JHHMMSS+DDMMSS
in Simbad) (1)
15- 22 F8.4 deg RAdeg Right Ascension in decimal degrees (J2000)
24- 31 F8.4 deg DEdeg Declination in decimal degrees (J2000)
33- 37 F5.2 mag imag SDSS i band candidate deflector magnitude
39- 43 F5.3 --- zphot ? Coupon et al. (2009A&A...500..981C 2009A&A...500..981C)
photometric redshift
45- 49 F5.3 --- zd ? Deflector redshift
51- 55 F5.3 --- zs ? Source redshift
57 I1 --- qflag [2/3]? Quality factor (2)
59 I1 --- Confirm [0/3]? Confirmed code (3)
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Note (1): Systems are sorted in ascending name order with a first block of
qflag=3 values first, followed by a block of qflag=2.
Note (2): Factor as follows:
2 = probably a lens;
3 = definitely a lens.
Note (3): The follow-up confirmation flags are also listed when some additional
dataset brought firmer pieces of evidence on the nature of the candidate
previously classified as either a good candidate qflag=2 or an excellent
candidate qflag=3.
0 = not a lens;
1 = possibly a lens;
2 = probably a lens;
3 = definitely a lens.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 13-Jun-2017