The number density of superdense early-type galaxies at 1<z<2 and the
  local cluster galaxies
  Many of the early-type galaxies observed so far at z>1 turned out to have
smaller radii with respect to that of a typical present-day early-type galaxy
with comparable mass. This has generated the conviction that in the past
early-type galaxies were more compact, hence denser, and that as a consequence,
they should have increased their radius across the time to reconcile with the
present-day ones. However, observations have not yet established whether the
population of early-types in the early Universe was fully represented by
compact galaxies nor if they were so much more numerous than in the present-day
Universe to require an evolution of their sizes. Here we report the results of
a study based on a complete sample of 34 early-type galaxies at
0.9<z_{spec}<1.92. We find a majority (62 per cent) of normal early-type
galaxies similar to typical local ones, co-existing with compact early-types
from ~2 to ~6 times smaller in spite of the same mass and redshift. The
co-existence of normal and compact early-type galaxies at <z>~1.5 suggests that
their build-up taken place in the first 3-4 Gyr, followed distinct paths. Also,
we find that the number density of compact early-types at <z>~1.5 is consistent
with the lower limits of the local number density of compact early-types
derived from local clusters of galaxies. The similar number of compact
early-types found in the early and in the present day Universe frustrates the
hypothesized effective radius evolution while provides evidence that also
compact ETGs were as we see them today 9-10 Gyr ago. Finally, the fact that (at
least) most of the compact ETGs at high-z are accounted for by compact
early-types in local cluster of galaxies implies that the former are the direct
progenitors of the compact early-type cluster galaxies establishing a direct
link between environment and early phases of assembly of ETGs.
