The evolution of the galaxy sizes in the New Technology Telescope Deep Field: A comparison with cold dark matter models

The sizes of the held galaxies with I less than or equal to 25 have been me asured in the New Technology Telescope (NTT) Deep Field. Intrinsic sizes ha ve been obtained after deconvolution of the point-spread function with a mu lti-Gaussian method. The reliability of the method has been tested using bo th simulated data and Hubble Space Telescope (HST) observations of the same held. The distribution of the half-light radii is peaked at r(h1) similar or equal to 0." 3, in good agreement with that derived from HST images at t he same magnitude. An approximate morphological classification has been obt ained using the asymmetry and concentration parameters. The intrinsic sizes of the galaxies are shown as a function of their redshifts and absolute ma gnitudes using photometric redshifts derived from the multicolor catalog. W hile the brighter galaxies with morphological parameters typical of the nor mal spirals show a flat distribution in the range r(d) = 1 - 6 kpc, the fai nter population at 0.4 < z < 0.8 dominates at small sizes. To explore the s ignificance of this behavior, an analytical rendition of the standard cold dark matter model for the disk size evolution has been computed. The model showing the best fit to the local luminosity function and the Tully-Fisher relation is able to reproduce at intermediate redshifts a size distribution in general agreement with the observations, although it tends to underesti mate the number of galaxies fainter than M-B similar to -19 with disk sizes r(d) similar to 1-2 kpc.