The cosmic assembly of stellar haloes in massive Early-Type Galaxies
  Using the exquisite depth of the Hubble Ultra Deep Field (HUDF12 programme)
dataset, we explore the ongoing assembly of the outermost regions of the most
massive galaxies ($\rm M_{\rm stellar}\geq$ 5$\times$10$^{10}$ M$_{\odot}$) at
$z \leq$ 1. The outskirts of massive objects, particularly Early-Types Galaxies
(ETGs), are expected to suffer a dramatic transformation across cosmic time due
to continuous accretion of small galaxies. HUDF imaging allows us to study this
process at intermediate redshifts in 6 massive galaxies, exploring the
individual surface brightness profiles out to $\sim$25 effective radii. We find
that 5-20\% of the total stellar mass for the galaxies in our sample is
contained within 10 $< R <$ 50 kpc. These values are in close agreement with
numerical simulations, and higher than those reported for local late-type
galaxies ($\lesssim$5\%). The fraction of stellar mass stored in the outer
envelopes/haloes of Massive Early-Type Galaxies increases with decreasing
redshift, being 28.7\% at $< z > =$ 0.1, 15.1\% at $< z > =$ 0.65 and 3.5\% at
$< z > =$ 2. The fraction of mass in diffuse features linked with ongoing minor
merger events is $>$ 1-2\%, very similar to predictions based on observed close
pair counts. Therefore, the results for our small albeit meaningful sample
suggest that the size and mass growth of the most massive galaxies have been
solely driven by minor and major merging from $z =$ 1 to today.
