The evolution of galactic discs

We use recent observations of high-redshift galaxies to study the evolution of galactic discs over the redshift range 0 < z less than or similar to 1. The data are inconsistent with models in which discs were already assembled at z = 1 and have evolved only in luminosity since that time. Assuming that disc properties change with redshift as powers of 1 + z and analysing the observations assuming an Einstein-de Sitter universe, we find that for given rotation speed, disc scalelength decreases with z as similar to(1 + z)(-1), total B-band mass-to-light ratio decreases with z as similar to(1 + z)(-1), and disc luminosity (again in B) depends only weakly on z. These scalings are consistent with current data on the evolution of disc galaxy abundance as a function of size and luminosity. Both the scalings and the abundance evolution are close to the predictions of hierarchical models for galaxy formation. If different cosmogonies are compared, the observed evolution in disc size and disc abundance favours a hat low-Omega(0) universe over an Einstein-de Sitter universe.