The surface brightness of the Galaxy at the solar neighbourhood

We present a new determination of the surface brightness of our Galaxy at the Solar Neighbourhood as observed from outside the Galaxy. We rely on various existing optical and infra-red surveys to obtain a multiwavelength estimate. On the one hand, scattered light does not contribute significantly to the surface brightness. On the other hand, optical and infrared integrated all-sky surveys ( Pioneer 10/11 and COBE/DIRBE) show a systematically larger value than our synthetic local estimate based on Hipparcos data. This local estimate is also compatible with our Galactic simulations normalised at the Solar Neighbourhood and assuming a homogeneous stellar distribution. We interpret this disagreement as a signature of the presence of a local minimum of the stellar density compatible with Gould's belt. According to this result, the global luminosity of the MilkyWay should follow the Tully-Fisher relation established for external galaxies.