Puffing up early-type galaxies by baryonic mass loss: numerical
  experiments
  Observations performed in the last few years indicate that most massive
early-type galaxies (ETGs) observed at redshift z>1 exhibit sizes smaller by a
factor of a few than local ETGs of analogous stellar mass. We present numerical
simulations of the effect of baryonic mass loss on the structure of a
spheroidal stellar system, embedded in a dark matter halo. This process,
invoked as a possible explanation of the observed size increase of ETGs since z
\sim 2, could be caused either by QSO/starburst driven galactic winds, promptly
ejecting from Early Type Galaxies (ETGs) the residual gas and halting star
formation (galactic winds), or by stellar mass returned to the ISM in the final
stages of stellar evolution. Indeed, we find that a conceivable loss of about
50% of the baryonic mass can produce a significant size increase. However, the
puffing up due to galactic winds occurs when the stellar populations are much
younger than the estimated ages >0.5 Gyr of compact high-z ETGs. Therefore,
while it may have had a role in deciding the final structure of ETGs, it cannot
explain the evolution observed so far of their size-mass relation; its
signature should be searched for in much younger systems. Conversely, the mass
loss due to stellar evolution could cause a relatively modest expansion of
passively evolving stellar systems later on, contributing to, without
dominating, the observed evolution of their mass-size relationship.
