Comparing the evolution of the galaxy disk sizes with cold dark matter models: The Hubble Deep Field

The intrinsic sizes of the field galaxies with I I 26 in the Hubble and ESO New Technology Telescope (NTT) Deep Fields are shown as a function of thei r redshifts and absolute magnitudes using photometric redshifts derived fro m the multicolor catalogs and are compared with the cold dark matter (CDM) predictions. Extending to the lower luminosities and to the higher z that o ur previous analysis performed on the NTT field alone, we find the distribu tion of the galaxy disk sizes at different cosmic epochs is within the rang e predicted by typical CDM models. However, the observed size distribution of faint (M-B > -19) galaxies is skewed with respect to the CDM predictions , and an excess of small-size disks (R-d < 2 kpc) is already present at z s imilar to 0.5. The excess persists up to z similar to 3 and involves bright er galaxies. Such an excess may be reduced if luminosity-dependent effects, like starburst activity in interacting galaxies, are included in the physi cal mechanisms governing the star formation history in CDM models.