An extended stellar halo discovered in the Fornax dwarf spheroidal using
  Gaia EDR3
  We have studied the extent of the Red Giant Branch stellar population in the
Fornax dwarf spheroidal galaxy using the spatially extended and homogeneous
data set from Gaia EDR3. Our preselection of stars belonging to Fornax is based
on their proper motions, parallaxes and color-magnitude diagram. The latter
criteria provide a Fornax star sample, which we further restrict by color 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 to 0.3%), 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% of the stellar mass of Fornax, and behaves like an extended halo. The
absence of tidally elongated features at such an unprecedented depth
(equivalent to $37.94\pm0.16$ mag ${\rm arcsec}^{-2}$ in V-band) rules out a
possible role of tidal stripping. We suggest instead that Fornax is likely at
first infall, and has lost its gas very recently, which consequently leads to a
lack of gravity implying that residual stars have spherically expanded to form
the newly discovered stellar halo of Fornax.
