EDP Sciences
Free access
Issue
A&A
Volume 405, Number 2, July II 2003
Page(s) 415 - 424
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20030614


A&A 405, 415-424 (2003)
DOI: 10.1051/0004-6361:20030614

LBQS 1429-0053: A binary quasar rather than a lensed quasar

C. Faure1, 2, D. Alloin1, S. Gras1, F. Courbin3, J.-P. Kneib2, 4 and P. Hudelot2

1  European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
2  Observatoire Midi-Pyrénées, UMR 5572, 14 avenue Edouard Belin, 31400 Toulouse, France
3  Institut d'Astrophysique et de Géophysique, Faculté des Sciences, Université de Liège, Allée du 6 août, 17, B5C, Liège 1, Belgium
4  Caltech Astronomy Department, Mail Code 105-24, Pasadena, CA 91125, USA

(Received 20 December 2002 / Accepted 27 March 2003)

Abstract
Very deep ESO/VLT FORS1 and ISAAC images, as well as HST NICMOS2 data are used to infer the nature of the quasar pair LBQS 1429-0053 A and B, either a binary quasar or a doubly-imaged lensed quasar. Direct search of a putative lensing galaxy is unsuccessful down to R=27, J=24, Ks=22.5 and H=22.5. Moreover, no galaxy overdensity close to the quasar pair is found. A weak shear analysis of the FORS1 R-band 6.8´ $\times$ 6.8´ field also fails at detecting any concentration of dark matter more massive than $\sigma=500$ km s -1 and weakens the hypothesis of a dark lens. The only sign of a possible lens consists in a group of 5 objects having colors consistent with galaxies at $z \sim 1$, within a radius of 5´´ from the quasar pair. Considering this group as the lensing potential does not allow to reproduce the image position and flux ratio of LBQS 1429-0053 A and B. Our deep R-band image shows a blue, previously unknown, extended object at the position of LBQS 1429-0053 A, which is consistent with either being the lensed quasar A host, or being an intervening galaxy at lower redshift. Unless future very deep optical images demonstrate that this object is actually the lensed host of LBQS 1429-0053, we conclude that there is very little evidence for LBQS 1429-0053 being lensed. Therefore, we are led to declare LBQS 1429-0053 A and B a genuine binary quasar.


Key words: galaxies: clusters: general -- gravitational lensing -- quasar: individual: LBQS 1429-0053

Offprint request: C. Faure, cfaure@eso.org

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