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We investigate the properties of a clump-cluster galaxy at redshift 1.57. Themorphology of this galaxy is dominated by eight star-forming clumps in opticalobservations, and has photometric properties typical of most clump-cluster andchain galaxies. Its complex asymmetrical morphology has led to the suggestionthat this system is a group merger of several initially separateproto-galaxies. We performed H_alpha integral field spectroscopy of this systemusing SINFONI on VLT UT4. These observations reveal a large-scale velocitygradient throughout the system, but with large local kinematic disturbances.Using a numerical model of gas-rich disk fragmentation, we find that clumpinteractions and migration can account for the observed disturbed rotation. Onthe other hand, the global rotation would not be expected for a multiplymerging system. We further find that this system follows the stellar mass vs.metallicity, star formation rate and size relations expected for a disk at thisredshift, and exhibits a disk-like radial metallicity gradient, so that thescenario of internal disk fragmentation is the most likely one. A red andmetallic central concentration appears to be a bulge in this proto-spiralclumpy galaxy. A chain galaxy at redshift 2.07 in the same field also showsdisk-like rotation. Such systems are likely progenitors of the present-daybright spiral galaxies, forming their exponential disks through clump migrationand disruption and fueling their bulges. Our present results show thatdisturbed morphologies and kinematics are not necessarily signs of galaxymergers and interactions, and can instead result from the internal evolution ofprimordial disks.

Observations and modelling of a clumpy galaxy at z=1.6: Spectroscopic clues to the origin and evolution of chain galaxies