Star formation in High Redshift Galaxies

The Hubble Space Telescope for optical and near-infrared light has opened up a view of star formation in young galaxies that has never been possible before. Because the most distant galaxies are viewed as they were when light left them long ago, we can see the various steps of galaxy formation through time. Our work in the last five years has concentrated on the
nature of star formation in these galaxies, many of which are peculiar by the standards of our own neighborhood. The dominant peculiarity is the presence of enormous young clusters and star complexes in the disk systems. These complexes are 100 times more massive than star forming regions in galaxies today, and yet they appear to form by standard processes, which begin with a localized collapse of disk gas. Highly turbulent conditions are required. Numerical simulations suggest that clump formation is followed by clump migration to the center of the galaxy, where the largest clumps can merge into a bulge. This process seems to accompany the growth of galaxy disks over cosmic time, indicating that the growth occurs primarily by the rapid accretion of gas for systems that end up as spirals. Clumpy disk star formation precedes the formation of spirals and ellipticals, going back to at least a redshift of 5. Thus most star formation in the Universe appear to begin in disk systems, and from these, all of today's Hubble types eventually form.