On the formation of massive galaxies: A simultaneous study of number
  density, size and intrinsic colour evolution in GOODS
  The evolution of number density, size and intrinsic colour is determined for
a volume-limited sample of visually classified early-type galaxies selected
from the HST/ACS images of the GOODS North and South fields (version 2). The
sample comprises 457 galaxies over 320 arcmin2 with stellar masses above 3E10
Msun in the redshift range 0.4<z<1.2. Our data allow a simultaneous study of
number density, intrinsic colour distribution and size. We find that the most
massive systems (>3E11 Msun) do not show any appreciable change in comoving
number density or size in our data. Furthermore, when including the results
from 2dFGRS, we find that the number density of massive early-type galaxies is
consistent with no evolution between z=1.2 and 0, i.e. over an epoch spanning
more than half of the current age of the Universe. Massive galaxies show very
homogeneous **intrinsic** colour distributions, featuring red cores with small
scatter. The distribution of half-light radii -- when compared to z=0 and z>1
samples -- is compatible with the predictions of semi-analytic models relating
size evolution to the amount of dissipation during major mergers. However, in a
more speculative fashion, the observations can also be interpreted as weak or
even no evolution in comoving number density **and size** between 0.4<z<1.2,
thus pushing major mergers of the most massive galaxies towards lower
redshifts.
