Restrictions to the galaxy evolutionary models from the Hawaiian Deep Fields SSA13 and SSA22

Abstract

Quantitative structural analysis of the galaxies present in the Hawaiian Deep Fields SSA13 and SSA22 is reported. The structural parameters of the galaxies have been obtained automatically by fitting a two-component model (Sersic r^{1/n} bulge and exponential disc) to the surface brightness of the galaxies. The galaxies were classified on the basis of the bulge-to-total luminosity ratio (B/T). The magnitude selection criteria and the reliability of our method have been checked by using Monte Carlo simulations. A complete sample of objects up to redshift 0.8 has been achieved. Spheroidal objects (E/S0) represent ~33% and spirals ~41% of the total number of galaxies, while mergers and unclassified objects represent ~26%. We have computed the comoving space density of the different kinds of objects. In an Einstein-de Sitter universe a decrease in the comoving density of E/S0 galaxies is observed as redshift increases (a ~30% less at z=0.8), while for spiral galaxies a relatively quiet evolution is reported. The framework of hierarchical clustering evolution models of galaxies seems to be the most appropriate to explain our results.