The sources of extended continuum emission towards Q 0151 + 048 A : The host galaxy and the Damped Ly α Absorber ⋆

We present deep imaging in the U, B and I bands obtained under excellent seeing conditions of the double quasar Q0151+048A,B and of the Damped Lyα (DLA) absorbing galaxy at zabs = 1.9342 named S4. We analyse the data employing two separate and independent methods. First we deconvolve the images using the MCS algorithm, secondly we decompose the images via an object based iteration process where we fit models to objects without any attempt to improve the resolution of the data. Our detailed analysis of the images reveals, somewhat surprisingly, that extended objects centred on the quasars themselves are much brighter continuum sources than the DLA galaxy. Due to the complexity caused by the many superimposed objects, we are unable to certify whether or not continuum emission from the DLA galaxy is detected. Continuum emission from the extended objects centred on the positions of the quasars is clearly seen, and the objects are tentatively identified as the “host galaxies” of the quasars. The flux of those host galaxies is of order 2–6% of the quasar flux, and the light profile of the brighter of the two is clearly best fit with a de Vaucouleurs profile. We discuss two alternative interpretations of the origin of the extended flux: i) the early stage of a massive elliptical galaxy in the process of forming the bulk of its stars, and ii) quasar light scattered by dust.