PROBABILISTIC REPRESENTATION OF THE GAIA EXTRAGALACTIC REFERENCE FRAME

摘要

The Gaia extragalactic reference frame (GCRF) will be formed by about 500 000 quasars, to a positional precision reaching 50 μas. The GCRF is a key factor for several of the Gaia science goals, and it is important to access its sky and magnitude distribution before the mission launch. Despite recent in-depth investigations, such as the 2dF and SLOAN, there is no all-sky account to such. Hitherto, to the M = 20 limit, the USNO B1.0 and GSC2 catalogues attain completeness. They can thus be used to generate an accurate probabilistic description of the GCRF. Starting from those catalogues, the main strategies that are brought into play for the task involve determination of the quasars loci in the proper motions space; in the colour/colour space; in the broad-band spec-troscopy space; and in the probability space as given by the stars and extragalactic objects distribution models. Here we discuss such strategies and some of the obtained results.