Massive and old quiescent galaxies at high redshift
  Massive quiescent galaxies at high redshift can shed light on the processes
of galaxy mass assembly and quenching of the star formation at early epochs. We
present observer-frame color-color diagrams designed to identify candidate
quiescent galaxies from z=2.5 up to the highest redshifts, that can be then be
selected for spectroscopic follow-up observations. The application to the
COSMOS2015 catalog shows that, after refining the selection with SED fitting,
the number of massive old quiescent galaxies exceeds the forecast of
state-of-the-art semi-analytic models, pointing out the need of an improvement
of the implemented quenching mechanisms at high redshifts.
