  Spectroscopic redshifts have been measured for 9 K-band luminous galaxies at
1.7 < z < 2.3, selected with Ks < 20 in the "K20 survey" region of the Great
Observatories Origins Deep Survey area. Star formation rates (SFRs) of ~100-500
Msun/yr are derived when dust extinction is taken into account. The fitting of
their multi-color spectral energy distributions indicates stellar masses M ~
10^11 Msun for most of the galaxies. Their rest-frame UV morphology is highly
irregular, suggesting that merging-driven starbursts are going on in these
galaxies. Morphologies tend to be more compact in the near-IR, a hint for the
possible presence of older stellar populations. Such galaxies are strongly
clustered, with 7 out of 9 belonging to redshift spikes, which indicates a
correlation length r_0 ~ 9-17 h^-1 Mpc (1 sigma range). Current semianalytical
models of galaxy formation appear to underpredict by a large factor (about 30)
the number density of such a population of massive and powerful starburst
galaxies at z ~ 2. The high masses and SFRs together with the strong clustering
suggest that at z ~ 2 we may have started to explore the major formation epoch
of massive early-type galaxies.
