Star formation and quenching among the most massive galaxies at z~1.7
  We have conducted a detailed object-by-object study of a mass-complete
(M*>10^11 M_sun) sample of 56 galaxies at 1.4 < z < 2 in the GOODS-South field,
showing that an accurate de-blending in MIPS/24um images is essential to
properly assign to each galaxy its own star formation rate (SFR), whereas an
automatic procedure often fails. This applies especially to galaxies with SFRs
below the Main Sequence (MS) value, which may be in their quenching phase.
After that, the sample splits evenly between galaxies forming stars within a
factor of 4 of the MS rate (~45%), and sub-MS galaxies with SFRs ~10-1000 times
smaller (~55%). We did not find a well defined class of intermediate, transient
objects below the MS, suggesting that the conversion of a massive MS galaxy
into a quenched remnant may take a relatively short time (<1 Gyr), though a
larger sample should be analyzed in the same way to set precise limits on the
quenching timescale. X-ray detected AGNs represent a ~30% fraction of the
sample, and are found among both star-forming and quenched galaxies. The
morphological analysis revealed that ~50% of our massive objects are
bulge-dominated, and almost all MS galaxies with a relevant bulge component
host an AGN. We also found sub-MS SFRs in many bulge-dominated systems,
providing support to the notion that bulge growth, AGN activity and quenching
of star formation are closely related to each other.
