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

Abstract

A substantial population of high redshift early-type galaxies is detected in very deep UBVRIJHK images towards the HDF-South. Four elliptical profile galaxies are identified in the redshift range z=1-2, all with very red SEDs, implying ages of >2 Gyrs for standard passive evolution. We also find later type IR-luminous galaxies at similarly high redshift, (10 objects with z>1, H<25), whose weak UV emission implies single burst ages of >1 Gyr. The number and luminosity-densities of these galaxies are comparable with the local E/SO-Sbc populations for Ω_m>0.2, and in the absence of a significant cosmological constant, we infer that the major fraction of luminous Hubble-sequence galaxies have evolved little since z~2. A highly complete photometric redshift distribution is constructed to H=25 (69 galaxies) showing a broad spread of redshift, peaking at z~1.5, in reasonable agreement with some analyses of the HDF. Five `dropout&#39; galaxies are detected at z~3.8, which are compact in the IR, ~0.5 kpc/h at rest 3500Å. No example of a blue IR luminous elliptical is found, restricting the star-formation epoch of ellipticals to z>10 for a standard IMF and modest extinction.