  We investigate the properties of a clump-cluster galaxy at redshift 1.57. The
morphology of this galaxy is dominated by eight star-forming clumps in optical
observations, and has photometric properties typical of most clump-cluster and
chain galaxies. Its complex asymmetrical morphology has led to the suggestion
that this system is a group merger of several initially separate
proto-galaxies. We performed H_alpha integral field spectroscopy of this system
using SINFONI on VLT UT4. These observations reveal a large-scale velocity
gradient throughout the system, but with large local kinematic disturbances.
Using a numerical model of gas-rich disk fragmentation, we find that clump
interactions and migration can account for the observed disturbed rotation. On
the other hand, the global rotation would not be expected for a multiply
merging system. We further find that this system follows the stellar mass vs.
metallicity, star formation rate and size relations expected for a disk at this
redshift, and exhibits a disk-like radial metallicity gradient, so that the
scenario of internal disk fragmentation is the most likely one. A red and
metallic central concentration appears to be a bulge in this proto-spiral
clumpy galaxy. A chain galaxy at redshift 2.07 in the same field also shows
disk-like rotation. Such systems are likely progenitors of the present-day
bright spiral galaxies, forming their exponential disks through clump migration
and disruption and fueling their bulges. Our present results show that
disturbed morphologies and kinematics are not necessarily signs of galaxy
mergers and interactions, and can instead result from the internal evolution of
primordial disks.
