Evolution of morphology in the Chandra Deep Field South

Abstract

We studied the morphology of galaxies in the Chandra Deep Field South using ACS multi-wavelength data from the Great Observatories Origin Deep Survey and 524 spectroscopic redshifts from the VIMOS VLT Deep Survey completed with 2874 photometric redshift computed from COMBO-17 multi-color data. The rest-frame B-band makes it possible to discriminate two morphological types in an asymmetry-concentration diagram: bulge- and disk-dominated galaxies. The rest-frame color index $B-I$ is found to be very correlated with the morphological classification: wholly bulge-dominated galaxies are redder than disk-dominated galaxies. However color allowed us to distinguish a population of faint blue bulge-dominated galaxies ($B-I<0.9$), whose nature is still unclear. Using the rest-frame B-band classification from $z\sim0.15$ up to $z\sim1.1$, we quantified the evolution of the proportion of morphological types as a function of the redshift. Our large sample allowed us to compute luminosity functions per morphological type in rest-frame B-band. The bulge-dominated population is found to be composite: on the one hand the red ($(B-I)\_{AB}>0.9$), bright galaxies, which seem to increase in density toward low redshifts. On the other hand the blue, compact, faint bulge-dominated galaxies, strongly evolving with the redshift.