Detection of Evolved High-Redshift Galaxies in Deep NICMOS/VLT Impages

Abstract

A substantial population of high-redshift, early-type galaxies is detected in very deep UBVRIJHK images. Four elliptical profile galaxies are identified in the redshift range 1<z<2, with very red spectral energy distributions implying ages of >~2 Gyr for standard passive evolution. We also find later type IR-luminous galaxies at similarly high redshift (10 objects with z>1, H<25), with weak UV emission implying single-burst ages of >~1 Gyr. The number and luminosity densities of these galaxies are comparable to the local E/S0-Sbc populations for Ω_m>0.2, suggesting that the major fraction of luminous Hubble sequence galaxies has evolved little since z~2. A highly complete photometric redshift distribution is constructed to H=25 (69 galaxies) that shows a broad spread of redshift, peaking at z~1.5, in reasonable agreement with some analyses of the Hubble Deep Field. Four ``dropout'' galaxies are detected at z~3.8 and are compact in the IR, ~0.5 kpc h^-1 at rest frame 3500 Å. No example of a blue IR-luminous elliptical galaxy is found, thus restricting the star formation epoch of elliptical galaxies to z>=5-10 for a standard initial mass function and modest extinction.