Fornax dSph star members study with GaiaEDR3

Our pre-selection of stars belonging to Fornax is based on their proper motions, parallaxes, and colour-magnitude diagram. The latter criteria provide a Fornax star sample, which we further restrict by colour and magnitude to eliminate contaminations due to either Milky Way stars or QSOs.

The precision of the data has been sufficient to reach extremely small contaminations (0.02-0.3 per cent), allowing us to reach to a background level 12 magnitudes deeper than the central surface brightness of Fornax. We discover a break in the density profile, which reveals the presence of an additional component that extents 2.1 degree in radius, i.e. 5.4 kpc, and almost seven times the half-light radius of Fornax. The extended new component represents 10 per cent of the stellar mass of Fornax, and behaves like an extended halo.