J/MNRAS/466/3088 Lensed and extended quasars (Williams+, 2017)
Population mixtures and searches of lensed and extended quasars across
photometric surveys.
Williams P., Agnello A., Treu T.
<Mon. Not. R. Astron. Soc., 466, 3088-3102 (2017)>
=2017MNRAS.466.3088W 2017MNRAS.466.3088W (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Gravitational lensing
Keywords: gravitational lensing: strong - methods: statistical - catalogues
Abstract:
Wide-field photometric surveys enable searches of rare yet interesting
objects, such as strongly lensed quasars or quasars with a bright host
galaxy. Past searches for lensed quasars based on their optical and
near-infrared properties have relied on photometric cuts and
spectroscopic preselection (as in the Sloan Quasar Lens Search), or
neural networks applied to photometric samples. These methods rely on
cuts in morphology and colours, with the risk of losing many
interesting objects due to scatter in their population properties,
restrictive training sets, systematic uncertainties in catalogue-based
magnitudes and survey-to-survey photometric variations. Here, we
explore the performance of a Gaussian mixture model to separate
point-like quasars, quasars with an extended host and strongly lensed
quasars using grizpsf and model magnitudes and WISEW1, W2. The choice
of optical magnitudes is due to their presence in all current and
upcoming releases of wide-field surveys, whereas UV information is not
always available. We then assess the contamination from blue galaxies
and the role of additional features such as W3 magnitudes or psf-model
terms as morphological information. As a demonstration, we conduct a
search in a random 10 per cent of the SDSS footprint, and provide the
catalogue of the 43 SDSS object with the highest 'lens' score in our
selection that survive visual inspection, and are spectroscopically
confirmed to host active nuclei. We inspect archival data and find
images of 5/43 objects in the Hubble Legacy Archive, including two
known lenses.
Description:
We finalize our tests of the Gaussian mixture model by examining how
it classifies known lenses. Of a list of known lenses, 128 lie in the
SDSS footprint for which we can obtain colours and calculate
membership probabilities (table 2).
From our visual inspection scores, we have 43 objects with score
greater than 1.5, after eliminating all contaminants based on the
spectroscopic information. These are listed in Table 3
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 89 128 List of all known lenses in SDSS, along with
selected membership probabilities
table3.dat 102 43 *Coordinates and colours of the 43 SDSS objects
selected by visual inspection.
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Note on table3.dat: The candidates are ranked primarily by visual inspection
score and secondarily by lens score.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name Name
21- 31 F11.7 deg RAdeg Right ascension (J2000)
33- 43 F11.7 deg DEdeg Declination (J2000)
45- 51 F7.5 --- p(lens) Probability of lensed QSO
53- 59 F7.5 --- p(PLQSO) Probability of point-like QSO, all redshifts
61- 67 F7.5 --- p(ExtQSO1) Probability of extended QSO, 1.2<z<1.75
69- 75 F7.5 --- p(ExtQSO2) Probability of extended QSO, 1.75<z<2.4
77- 83 F7.5 --- p(ExtQSO3) Probability of extended QSO, z>2.4
85- 89 F5.2 arcsec Sep Separation
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 11 F11.7 deg RAdeg Rigth ascension (J2000)
13- 22 F10.7 deg DEdeg Declination (J2000)
24- 28 F5.2 mag umag SDSS u magnitude (AB)
30- 34 F5.2 mag gmag SDSS g magnitude (AB)
36- 40 F5.2 mag rmag SDSS r magnitude (AB)
42- 46 F5.2 mag imag SDSS i magnitude (AB)
48- 52 F5.2 mag zmag SDSS z magnitude (AB)
54- 58 F5.2 mag W1mag WISE W1 magnitude (Vega)
60- 64 F5.2 mag W2mag WISE W2 magnitude (Vega)
66- 70 F5.2 mag gmagpsf SDSS PSF g magnitude (AB)
72- 76 F5.2 mag rmagpsf SDSS PSF r magnitude (AB)
78- 82 F5.2 mag imagpsf SDSS PSF i magnitude (AB)
84- 88 F5.2 mag W3mag WISE W3 magnitude (Vega)
90- 94 F5.3 --- z Redshift
96-102 F7.5 --- p(lens) Lensing QSO probability
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 23-Oct-2019