* Astronomy

Title: A sharp look at the gravitationally lensed quasar SDSS J0806+2006 with Laser Guide Star Adaptive Optics
Authors: D. Sluse, F. Courbin, A. Eigenbrod, G. Meylan (Laboratoire d'astrophysique, Ecole Polytechnique Fédérale de Lausanne-EPFL)

We present the first VLT near-IR observations of a gravitationally lensed quasar, using Adaptive Optics and Laser Guide Stars. These observations can be considered as a test bench for future systematic observations of lensed quasars with Adaptive Optics, even when bright natural guide stars are not available in the nearby field. With only 14 minutes of observing time, we derive very accurate astrometry of the quasar images and of the lensing galaxy, with 0.05\arcsec spatial resolution, comparable with the HST. In combination with deep VLT optical spectra of the quasar images, we use our Adaptive Optics images in order to constrain simple models for the mass distribution in the lensing galaxy. We find that the latter is almost circular and does not need any strong external shear to fit the data, hence making SDSS J0806+2006, a clean lens for cosmological applications. The time delay predicted for SDSS J0806+2006, assuming a singular isothermal ellipsoid model and the concordance cosmology, is \Delta t ~= 36.5 days. Our optical spectra indicate a flux ratio between the quasar images of A/B=1.3 in the continuum and A/B=2.2 both in the MgII and in the CIII] broad emission lines. This suggests that microlensing affects the continuum emission. However, the constant ratio between the two emission lines indicates that the BEL are not microlensed. Finally, we see no evidence for reddening by dust in the lensing galaxy.

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