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

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

Corresponding author: C. Faure, cfaure@eso.org

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 , , and . Moreover, no galaxy overdensity close to the quasar pair is found. A weak shear analysis of the FORS1 R-band 6.8´  6.8´  field also fails at detecting any concentration of dark matter more massive than  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 , 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.