About the origin of extinction in the gravitational lens system MG J0414+0534

Photometric measurements of the highly reddened gravitational mirage MG J0414+0534 have been carried out either by PSF subtraction or by applying accurate deconvolution algorithms to optical (R, I) and near-infrared (K) images obtained at CFHT and NOT under sub-arcsecond seeing conditions. It is confirmed that the close pair of images A1-A2 suffers a larger extinction than B and C. While the colours of image A2 obtained from ground-based data seem inconsistent with a simple reddening law, higher resolution images available from HST archives reveal an additional extended component (arc) which introduces significant errors in the photometric decomposition. When the arc component is properly taken into account, the colours of the 4 nucleus images do agree with a classical reddening law, with A2 being by far the most obscured component. Such a differential extinction (maximum difference Delta E(R-I) =~ 0.6) is likely due to the lensing galaxy. This does not mean that {all} the extinction occurs into the lens. Indeed, the fact that the arc is much less red than the images of the nucleus suggests that an important part of the reddening is intrinsic to the source. Finally, no significant variability is observed within this data set, i.e. between 1994 and 1997, while a discrepancy from earlier data is noticed for (A1 + A2). Based on observations collected with the Canada-France-Hawaii Telescope at Mauna Kea (Hawaii, USA), the Nordic Optical Telescope (Canary, Spain) and archive data from the Hubble Space Telescope (NASA/ESA