Giant clumps are a characteristic feature of observed high-redshift disk galaxies .
We propose that these kpc-sized clumps have a complex substructure and are the result of many smaller clumps self-organizing themselves into clump clusters ( CC ) .
This bottom-up scenario is in contrast to the common top-down view that these giant clumps form first and then sub fragment .
Using a high resolution hydrodynamical simulation of an isolated , fragmented massive gas disk and mimicking the observations from Genzel et al .
( 32 ) at z \sim 2 , we find remarkable agreement in many details .
The CCs appear as single entities of sizes R _ { \mathrm { HWHM } } \simeq 0.9 - 1.4 kpc and masses \sim 1.5 - 3 \times 10 ^ { 9 } \mathrm { M _ { \sun } } representative of high-z observations .
They are organized in a ring around the center of the galaxy .
The origin of the observed clumps ’ high intrinsic velocity dispersion \sigma _ { \mathrm { intrinsic } } \simeq 50 - 100 \mathrm { km s ^ { -1 } } is fully explained by the internal irregular motions of their substructure in our simulation .
No additional energy input , e.g .
via stellar feedback , is necessary .
Furthermore , in agreement with observations , we find a small velocity gradient V _ { \mathrm { grad } } \simeq 8 - 27 \mathrm { km s ^ { -1 } kpc ^ { -1 } } along the CCs in the beam smeared velocity residual maps which corresponds to net prograde and retrograde rotation with respect to the rotation of the galactic disk .
The CC scenario could have strong implications for the internal evolution , lifetimes and the migration timescales of the observed giant clumps , bulge growth and AGN activity , stellar feedback and the chemical enrichment history of galactic disks .