3-D structure of the Galactic interstellar matter: A contribution from GAIA

We investigate the possibilities for tracing interstellar extinction with the ESA's astrometric space mission GAIA. The analysis is based on detailed simulations of the GAIA photometry, which are used to derive the distribution of interstellar matter in a modelled Galaxy. We find that `small' diffuse clouds (diameter D = 4 pc, EB-V = 0.06) will be easily traced with GAIA up to the distances of similar to 800 pc. `Large' diffuse interstellar clouds (D = 10 pc, EB-V = 0.13) will be located up to the distances of similar to 2.5 kpc. This holds for the reddening tracers of spectral types O - K2 brighter than V = 17. In most cases, due to their low spatial density, the early type stars (O - A2) cannot provide reliable information about the distribution of interstellar matter. None of the reddening tracers measured by GAIA will provide reliable identification of the individual interstellar clouds beyond the distances of similar to 3 kpc. Therefore, we conclude that the information available from photometric observations will be not sufficient for the detailed reconstruction of the 3-D distribution of Galactic interstellar matter. It is therefore extremely important to define the new strategies which would allow to combine all the available information, including the earlier space- and/or ground-based investigations, together with the information which will be provided by GAIA itself (parallaxes, EB-V etc.).