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 their redshifts and absolute magnitudes using photometric redshifts derived from the multicolor catalogs and are compared with the cold dark matter (CDM) predictions. Extending to the lower luminosities and to the higher z that our previous analysis performed on the NTT field alone, we find the distribution of the galaxy disk sizes at different cosmic epochs is within the range 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 similar to 0.5. The excess persists up to z similar to 3 and involves brighter galaxies. Such an excess may be reduced if luminosity-dependent effects, like starburst activity in interacting galaxies, are included in the physical mechanisms governing the star formation history in CDM models.