Near-Infrared Bright Galaxies at z~=2. Entering the Spheroid Formation Epoch?
Cimatti, A.; Daddi, E.; Tozzi, P.; Rosati, P.; Fontana, A.; di Serego Alighieri, S.; Nonino, M.; Mignoli, M.; Zamorani, G.; Pozzetti, L.; Broadhurst, T.; Renzini, A.; Conselice, C.; Vernet, J.
Germany, Italy, United States, Israel
Abstract
Spectroscopic redshifts have been measured for nine 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 (GOODS) area. Star formation rates (SFRs) of ~100-500 Msolar yr-1 are derived when dust extinction is taken into account. The fitting of their multicolor spectral energy distributions indicates stellar masses of M>~1011 Msolar 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 r0~9-17 h-1 Mpc (1 σ range). Current semianalytical models of galaxy formation appear to underpredict by a large factor (>~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.
Based on observations collected at the European Southern Observatory, Chile (ESO programs 70.A-0140 and 168.A-0485), and with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc, under NASA contract NAS5-26555.