EVOLUTION OF THE GALAXY POPULATION-BASED ON PHOTOMETRIC REDSHIFTS IN THE HUBBLE DEEP FIELD

This paper presents the results of a photometric redshift study of gal axies in the Hubble Deep Field (HDF). The method of determining redshi fts from broadband colors is described, and the dangers inherent in us ing it to estimate redshifts, particularly at very high z, are discuss ed. In particular, the need for accurate high-z spectral energy distri butions is illustrated. The validity of our photometric redshift techn ique is demonstrated both by direct verification with available HDF sp ectroscopic data and by comparisons of luminosity functions and lumino sity densities with those obtained from z < 1 spectroscopic redshift s urveys. Evolution of the galaxy population is studied over 0 less than or similar to z < 4. Brightening is seen in both the luminosity funct ion and the luminosity density out to z approximate to 3; this is foll owed by a decline in both at z > 3. A population of z < 0.5 star-formi ng dwarfs is observed to M(F450WAB) = -11. Our results are discussed i n the context of recent developments in the understanding of galaxy ev olution. (C) 1997 American Astronomical Society.