Program: GS-2005B-Q-4

The structure of the outer parts of galactic disks and the nature of their stellar populations are central to understanding the formation and evolution of spiral galaxies. We want to know how and when the outermost regions of the disks are assembled, so we need to know the age and metallicity distribution of the stars in these outermost regions. Our GMOS pilot observations showed that the stellar disk of NGC 300 continues its exponential decline without break out to a radius of at least 10 scalelengths, where the surface brightness is about 32 B mag arcsec^{-2}. This is the deepest observation of its kind to date. We now propose to study the stellar age and metallicity distribution in the outer disks of the pure disk galaxies NGC 300 and NGC 7793, using deep g' and i' images with GMOS.