Quantitative Morphology of Galaxies in the Hubble Deep Field

Abstract

We measure quantitative structural parameters of galaxies in the Hubble deep field (HDF) on the drizzled F814W images. Our structural parameters are based on a two-component surface brightness made up of a Sérsic profile and an exponential profile. We compare our results to the visual classification of van den Bergh et al. and the C-A classification of Abraham et al. Our morphological analysis of the galaxies in the HDF indicates that the spheroidal galaxies, defined here as galaxies with a dominant bulge profile, make up for only a small fraction, namely, 8%, of the galaxy population down to m_F814W(AB) = 26.0. We show that the larger fraction of early-type systems in the van den Bergh sample is primarily due to the difference in classification of 40% of small round galaxies with half-light radii less than 0.31". Although these objects are visually classified as elliptical galaxies, we find that they are disk dominated with bulge fractions less than 0.5. Given the existing large data set of HDF galaxies with measured spectroscopic redshifts, we are able to determine that the majority of distant galaxies (z > 2) from this sample are disk dominated. Our analysis reveals a subset of HDF galaxies that have profiles flatter than a pure exponential profile.