Q0045-3337: models including strong lensing by a spiral galaxy

¹ Institut für Theoretische Physik der Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland e-mail: [matteo;solar;jetzer]@physik.unizh.ch
² Dipartimento di Fisica e Matematica, Università dell'Insubria, via Valleggio 11, 22100 Como, Italy

Received: 29 November 2006
Accepted: 9 July 2007

Abstract

Aims.Falomo et al. (2005, A&A, 434, 469) discovered a disk-like galaxy at ~1.2 arcsec from the QSO Q0045-3337 by means of ESO VLT adaptive optics. They estimated a galaxy Einstein radius (for a point mass) of comparable size, thus suggesting the existence of a new, rare, spiral lens candidate, despite no evident image splitting. We discuss the possible lensing effect of the galaxy in more detail.

Methods.We performed two-dimensional surface photometry on the VLT image of the galaxy, confirming its spiral nature. We then verified if simple mass models, partially constrained by observational data, require unrealistic parameters to produce a still hidden second quasar image. We also evaluated the viability of an instrumental or a lensing origin of the observed QSO deformation.

Results.After galaxy model subtraction, we found a residual image, which we consider unlikely to be related to gravitational lensing. Existing data are not sufficient to assess the presence of image splitting, nor to constrain the number of images or discriminate between galaxy mass models.

Conclusions.Further observations are mandatory to progress in the study of this remarkable system, which could shed more light on the lensing behavior of spiral galaxies.