Abstract:

Context. The ESA Gaia mission, to be launched during 2013, will observe billions of objects, among which many galaxies, during its 5 yr scanning of the sky. This will provide a large space-based dataset with unprecedented spatial resolution. <BR /> Aims: Because of its natural Galactic and astrometric priority, Gaia's observational strategy was optimized for point sources. Nonetheless, it is expected that \~10⁶ sources will be extragalactic, and a large portion of them will be angularly small galaxies. Although the mission was designed for point sources, an analysis of the raw data will allow the recovery of morphology of those objects at a \~0.2'' level. This may constitute a unique all-sky survey of such galaxies. We describe the conceptual design of the method adopted for the morphological analysis of these objects as well as first results obtained from data simulations of low-resolution highly binned data. <BR /> Methods: First, the raw Gaia 1D observations are used to reconstruct a 2D image of the object - this image is known to contain artifacts and reconstruction signatures. Then, parameters characteristic of the reconstructed image are measured, and used for a purely morphological classification. Finally, based on the classification, a light profile is selected (pure-disk, disk+bulge, pure bulge, point source+disk, etc.) and fitted to all Gaia 1D observations simultaneously in a global process using forward modeling. <BR /> Results: Using simulations of Gaia observations from official Gaia Data Processing and Analysis Consortium tools, we were able to obtain the preliminary classification of the simulated objects at the \~83% level for two classes (ellipticals, spirals/irregulars) or at the \~79%, \~56%, and \~74% levels for three classes (E, S, and I). The morphological parameters of simulated object light profiles are recovered with errors at the following levels: -9 \plusmn 36% for the bulge radius, 11 \plusmn 53% for the bulge intensity, 1 \plusmn 4% for the disk radius, and -1 \plusmn 7% for the disk intensity. From these results, we conclude that it is possible to push the limits of the Gaia space mission by analysing galaxy morphology.