Fast evolving size of early-type galaxies at z>2 and the role of
  dissipationless (dry) merging
  We present the analysis of a large sample of early-type galaxies (ETGs) at
0<z<3 aimed at tracing the cosmic evolution of their size and compare it with a
model of pure dissipationless (dry) merging in the LambdaCDM framework. The
effective radius R_e depends on stellar mass M as R_e(M) \propto M}^{alpha}
with alpha ~ 0.5 at all redshifts. The redshift evolution of the mass- or
SDSS-normalized size can be reproduced as \propto (1+z)^beta with beta ~ -1,
with the most massive ETGs possibly showing the fastest evolutionary rate (beta
~ -1.4). This size evolution slows down significantly to beta ~ -0.6 if the
ETGs at z>2 are removed from the sample, suggesting an accelerated increase of
the typical sizes at z>2, especially for the ETGs with the largest masses. A
pure dry merging LambdaCDM model is marginally consistent with the average size
evolution at 0<z<1.7, but predicts descendants too compact for z>2 progenitor
ETGs. This opens the crucial question on what physical mechanism can explain
the accelerated evolution at z>2, or whether an unclear observational bias is
partly responsible for that.
