2007/01/05 by Debra Meloy Elmegreen, Bruce G. Elmegreen, Swara Ravindranath +1 · 1 citation
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1086/511667
40 pages, 13 figures, scheduled for ApJ Vol 658, April 1, 2007
arxiv created 2007/01/05 · arxiv updated 2015/06/24
The photometric redshift distributions, spectral types, Sersic indices, and sizes of all resolved galaxies in the Hubble Space Telescope Ultra Deep Field (UDF) are studied in order to understand the environment and nature of star formation in the early Universe. Clumpy disk galaxies that are bright at short wavelengths (restframe <5000 Angstroms) dominate the UDF out to z~5.5. Their uniformity in V/Vmax and co-moving volume density suggest they go even further, spanning a total time more than an order of magnitude larger than their instantaneous star formation times. They precede as well as accompany the formation epoch of distant red galaxies and extreme red objects. Those preceding could be the pre-merger objects that combined to make red spheroidal types at z~2 to 3. Clumpy disks that do not undergo mergers are likely to evolve into spirals. The morphology of clumpy disks, the size and separation of the clumps, and the prevalence of this type of structure in the early Universe suggests that most star formation occurs by self-gravitational collapse of disk gas.