Near-infrared bright galaxies at z≃2.: Entering the spheroid formation epoch

Spectroscopic redshifts have been measured for nine K-band luminous galaxies at 1.7<z<2.3, selected with K-s<20 in the K20 survey region of the Great Observatories Origins Deep Survey (GOODS) area. Star formation rates (SFRs) of similar to 100-500 M-circle dot yr(-1) are derived when dust extinction is taken into account. The fitting of their multicolor spectral energy distributions indicates stellar masses of M greater than or similar to 10(11) M-circle dot 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 seven out of nine belonging to redshift spikes, which indicates a correlation length of r(0)similar to 9-17 h(-1) Mpc (1 sigma range). Current semianalytical models of galaxy formation appear to underpredict by a large factor (greater than or similar to 30) the number density of such a population of massive and powerful starburst galaxies at z similar to 2. The high masses and SFRs, together with the strong clustering, suggest that at z similar to 2 we may have started to explore the major formation epoch of massive early-type galaxies.