Evolution of Disk Galaxies in the Goods-south Field: Number Densities and Size Distribution.1

We examine the evolution of the sizes and number densities of disk galaxies using the high resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). The multiwavelength images are used to classify galaxies based on their rest–frame B-band morphologies out to redshift z ∼ 1.25. In order to minimize the effect of selection biases, we confine our analysis to galaxies which occupy the region of magnitude-size plane where the survey is ∼ 90% complete at all redshifts. The observed size distribution is consistent with a log–normal distribution as seen for the disk galaxies in the local Universe and does not show any significant evolution over the redshift range 0.25≤ z ≤ 1.25. We find that the number densities of disk galaxies remains fairly constant over this redshift range, although a modest evolution by a factor of four may be possible within the 2σ uncertainties. Subject headings: galaxies: evolution — galaxies: formation — galaxies: fundamental parameters — galaxies: structure