Stellar haloes of disc galaxies at z~1
  Taking advantage of the ultra-deep near-infrared imaging obtained with the
Hubble Space Telescope on the Hubble Ultra Deep Field, we detect and explore
for the first time the properties of the stellar haloes of two Milky Way-like
galaxies at z~1. We find that the structural properties of those haloes (size
and shape) are similar to the ones found in the local universe. However, these
high-z stellar haloes are approximately three magnitudes brighter and exhibit
bluer colours ((g-r)<0.3 mag) than their local counterparts. The stellar
populations of z~1 stellar haloes are compatible with having ages <1 Gyr. This
implies that the stars in those haloes were formed basically at 1<z<2. This
result matches very well the theoretical predictions that locate most of the
formation of the stellar haloes at those early epochs. A pure passive
evolutionary scenario, where the stellar populations of our high-z haloes
simply fade to match the stellar halo properties found in the local universe,
is consistent with our data.
