DETECTION OF EVOLVED HIGH-REDSHIFT GALAXIES IN DEEP NICMOS/VLT IMAGES

摘要

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 > l, H < 25), with weak UV emission implying single-burst ages of > = I Gyt The number and luminosity densities of these galaxies are comparable to the local E/SO-Sbc populations for OMEGA-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 ~ l.5, in reasonable agreement with some analyses of the Hubble Deep Field. Four "dropout" galaxies are detected at z appro. = 3.8 and are compact in the IR, ~0.5 kpc h~-1 at rest frame 3500 A. 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.