Manuel Behrendt - February 3, 2016

Clusters of Small Clumps Can Explain The Peculiar Properties of Giant Clumps
in High-Redshift Galaxies

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 is in contrast to the common understanding that 
these giant clumps form first and then subfragment. 
Using a high resolution hydrodynamical simulation of an isolated, idealized 
gas disk we analyse the initial fragmentation process and the evolution of the 
clumps over several hundred Myrs. 
By mimicking the observations from Genzel et al. (2011) at z ~ 2 of the evolved
 disk, we find remarkable agreement in many details. The CCs appear as single 
entities of sizes R_HWHM ~0.9-1.4 kpc and masses of ~1.5-3 x 10^9 Msol 
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 ~50-100 km/s 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_grad ~8-27 km/s/kpc 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.