The Evolution of Field Spiral Galaxies over the Past 8 Gyr

We have performed a large observing campaign of intermediate–redshift disk galaxies including multi–object spectroscopy with the FORS instruments of the Very Large Telescope and imaging with the Advanced Camera for Surveys onboard the Hubble Space Telescope. Our data set comprises 113 late–type galaxies in the redshift range 0.1 2 m in rest– frame B. Numerous tests applied to the data confirm that this trend is unlikely to arise from an observational bias or systematic errors. Discrepancies between several previous studies could be explained as a combination of selection effects and small number statistics on the basis of such a mass–dependent luminosity evolution. On the other hand, this evolution would be at variance with the predictions from numerical simulations. For a given Vmax, the disks of the distant galaxies are slightly smaller than those of their local counterparts, as expected for a hierarchical structure growth. Hence, the discrepancy between the observations and theoretical predictions is limited to the properties of the stellar populations. A possible explanation could be the suppression of star formation in low–mass disks which is not yet properly implemented in models of galaxy evolution.