Satellites around massive galaxies since z$\sim$2: confronting the
  Millennium simulation with observations
  Minor merging has been postulated as the most likely evolutionary path to
produce the increase in size and mass observed in the massive galaxies since
z$\sim$2. In this Letter, we test directly this hypothesis comparing the
population of satellites around massive galaxies in cosmological simulations
versus the observations. We use state-of-the-art, publically available,
Millennium I and II simulations and the associated semi-analytical galaxy
catalogues to explore the time evolution of the fraction of massive galaxies
that have satellites, the number of satellites per galaxy, the projected
distance at which the satellite locate from the host galaxy, and the mass ratio
between the host galaxies and their satellites. The three virtual galaxy
catalogues considered here, overproduce the fraction of galaxies with
satellites by a factor ranging between 1.5 and 6 depending on the epoch,
whereas the mean projected distance and ratio of the satellite mass over host
mass are in closer agreement with data. The larger pull of satellites in the
semi-analytical samples could suggest that the size evolution found in previous
hydrodynamical simulations is an artifact due to the larger number of infalling
satellites compared to the real Universe. These results advise to revise the
physical ingredients implemented in the semi-analytical models in order to
reconcile the observed and computed fraction of galaxies with satellites, and
eventually, it would leave some room to other mechanisms explaining the galaxy
size growth not related to the minor merging.
