Evolution of spheroidal galaxies in the Hubble deep field

Using a new two-dimensional bulge-disk decomposition technique, which models the surface photometry of a galaxy with a two-component de Vaucouleurs and exponential light profile, we report on the photometry and structure of spheroidal galaxies in the Hubble Deep Field (HDF). The morphological analysis of the galaxies in the HDF indicate that the spheroidal galaxies, defined here as galaxies with a dominant bulge profile, make up only a small fraction of the galaxy population. This fraction is significantly smaller than seen among nearby galaxies, consistent with the idea that most of the nearby galaxies went through a past merger. The majority of those galaxies form a tight color-magnitude sequence extending to very red colors at faint magnitudes. By comparing with stellar population models, we note that the color range displayed by the spheroidal galaxies in the HDF is consistent with passive evolution.