The Fraction of Quiescent Massive Galaxies in the Early Universe
  Aims: The aim of this work is to collect a complete, mass--selected sample of
galaxies with very low specific star formation rate, for a comparison with the
prediction of recent theoretical models. Method: We use the 24/K flux ratio,
complemented by the SED fitting to the full 0.35-8.0 mum spectral distribution,
to select quiescent galaxies from z~0.4 to z~4 in the GOODS--MUSIC sample. Our
observational selection can be translated into thresholds on the specific star
formation rate SFR/M_*, that can be used to compare with the theoretical
predictions. Results: We find that, in the framework of the well known global
decline of the quiescent fraction with redshift, a non-negligible fraction
~15-20% of massive galaxies with very low specific star formation rate exists
up to z~4, including a tail of "Red&Dead" galaxies with SFR/M_*<10^{-11}/yr.
Recent theoretical models vary to a large extent in the prediction of the
fraction of galaxies with very low specific star formation rates, and are
unable to provide a global match to our data.
