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

Abstract

Aims. Falomo et al. (2005) 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 pointing up the existence of a new, rare, spiral lens candidate, despite no evident image splitting. Here we discuss the possible lensing effect of the galaxy in some 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 respective viability of an instrumental or a lensing origin of the observed QSO deformation. Results. After galaxy model subtraction, we found a residual image, likely not 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. Conclusion. Further observations are mandatory to progress in the study of this remarkable system, that could shed more light on the lensing behaviour of spiral galaxies.