Abstract
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 are single homogeneous objects. Using a high resolution hydrodynamical
simulation of an isolated, fragmented massive gas disk and mimicking the
observations from Genzel et al. (2011) at $z 2$, we find remarkable
agreement in many details. The CCs appear as single entities of sizes $R_HWHM
0.9-1.4$ kpc and masses $1.5-3 10^9 \ M_ødot$
representative of high-z observations. They are organized in a ring around the
center of the galaxy. The origin of the observed clump's high intrinsic
velocity dispersion $\sigma_intrinsic 50 - 100 \ km \ s^-1$ 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 $V_grad 8 - 27 \ km \ s^-1 \ kpc^-1$ 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.
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