VDES J2325-5229 a z=2.7 gravitationally lensed quasar discovered using morphology independent supervised machine learning
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Authors
Ostrovski, F
Connolly, AJ
Auger, Matthew
Hung, JM
Lidman, CE
Reed, Sophie
Allam, S
Benoit-Lévy, A
Bertin, E
Brooks, D
Buckley-Geer, E
Rosell, AC
Kind, MC
Carretero, J
Cunha, CE
Costa, LND
Desai, S
Diehl, HT
Dietrich, JP
Evrard, AE
Finley, DA
Flaugher, B
Fosalba, P
Frieman, J
Gerdes, DW
Goldstein, DA
Gruen, D
Gruendl, RA
Gutierrez, G
Honscheid, K
James, DJ
Kuehn, K
Kuropatkin, N
Lima, M
Lin, H
Maia, MAG
Marshall, JL
Martini, P
Melchior, P
Miquel, R
Ogando, R
Malagón, AP
Reil, K
Romer, K
Sanchez, E
Santiago, B
Scarpine, V
Sevilla-Noarbe, I
Soares-Santos, M
Sobreira, F
Suchyta, E
Tarle, G
Thomas, D
Tucker, DL
Walker, AR
Publication Date
2017-03-01Journal Title
Monthly Notices of the Royal Astronomical Society
ISSN
0035-8711
Publisher
Oxford University Press
Volume
465
Issue
4
Pages
4325-4334
Language
English
Type
Article
This Version
VoR
Metadata
Show full item recordCitation
Ostrovski, F., McMahon, R., Connolly, A., Lemon, C., Auger, M., Banerji, M., Hung, J., et al. (2017). VDES J2325-5229 a z=2.7 gravitationally lensed quasar discovered using morphology independent supervised machine learning. Monthly Notices of the Royal Astronomical Society, 465 (4), 4325-4334. https://doi.org/10.1093/mnras/stw2958
Abstract
We present the discovery and preliminary characterization of a gravitationally lensed quasar with a source redshift $\textit{zs}$ = 2.74 and image separation of 2.9 arcsec lensed by a foreground $\textit{zl}$ = 0.40 elliptical galaxy. Since optical observations of gravitationally lensed quasars show the lens system as a superposition of multiple point sources and a foreground lensing galaxy, we have developed a morphology-independent multi-wavelength approach to the photometric selection of lensed quasar candidates based on Gaussian Mixture Models (GMM) supervised machine learning. Using this technique and $\textit{gi}$ multicolour photometric observations from the Dark Energy Survey (DES), near-IR $\textit{JK}$ photometry from the VISTA Hemisphere Survey (VHS) and WISE mid-IR photometry, we have identified a candidate system with two catalogue components with $\textit{iAB}$ = 18.61 and $\textit{iAB}$ = 20.44 comprising an elliptical galaxy and two blue point sources. Spectroscopic follow-up with NTT and the use of an archival AAT spectrum show that the point sources can be identified as a lensed quasar with an emission line redshift of $\textit{z}$ = 2.739 ± 0.003 and a foreground early-type galaxy with $\textit{z}$ = 0.400 ± 0.002. We model the system as a single isothermal ellipsoid and find the Einstein radius θE ∼ 1.47 arcsec, enclosed mass $\textit{M}$enc ∼ 4 × 10$^{11}$$\textit{M}$⊙ and a time delay of ∼52 d. The relatively wide separation, month scale time delay duration and high redshift make this an ideal system for constraining the expansion rate beyond a redshift of 1.
Keywords
gravitational lensing: strong, methods: observational, methods: statistical, quasars: general
Sponsorship
FO is supported jointly by CAPES (the Science without Borders programme) and the Cambridge Commonwealth Trust. RGM, CAL, MWA, MB, SLR acknowledge the support of UK Science and Technology Research Council (STFC). AJC acknowledges the support of a Raymond and Beverly Sackler visiting fellowship at the Institute of Astronomy.
For further information regarding funding please visit the publisher's website.
Funder references
STFC (ST/K004182/1)
STFC (ST/M003914/1)
SCIENCE & TECHNOLOGY FACILITIES COUNCIL (ST/N004493/1)
SCIENCE & TECHNOLOGY FACILITIES COUNCIL (ST/N000927/1)
STFC (1369580)
STFC (1638336)
Identifiers
External DOI: https://doi.org/10.1093/mnras/stw2958
This record's URL: https://www.repository.cam.ac.uk/handle/1810/262695
Rights
Licence:
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