Clumpy Galaxies in GOODS and GEMS: Massive Analogs of Local Dwarf
  Irregulars
  Clumpy galaxies in the GEMS and GOODS fields are examined for clues to their
evolution into modern spirals. The magnitudes of the clumps and the surface
brightnesses of the interclump regions are measured and fitted to models of
stellar age and mass. There is an evolutionary trend from clump clusters with
no evident interclump emission to clump clusters with faint red disks, to
spiral galaxies of the flocculent or grand design types. Along this sequence,
the interclump surface density increases and the mass surface density contrast
between the clumps and the interclump regions decreases, suggesting a gradual
dispersal of clumps to form disks. Also along this sequence, the bulge-to-clump
mass ratios and age ratios increase, suggesting a gradual formation of bulges.
All of these morphological types occur in the same redshift range, indicating
that the clump cluster morphology is not the result of bandshifting.
Comparisons to local galaxies with the same rest wavelength and spatial
resolution show that clump clusters resemble local dwarf Irregulars. This
resemblance is consistent with a model in which the clumpy morphology comes
from gravitational instabilities in gas with a high turbulent speed compared to
the rotation speed and a high mass fraction compared to the stars.
