CLUMPY STAR-FORMING REGIONS AS THE ORIGIN OF THE PECULIAR MORPHOLOGY OF HIGH-REDSHIFT GALAXIES

Many high-redshift galaxies have peculiar morphologies and photometric properties(1-5). It is not clear whether these peculiarities originat e in galaxy-galaxy interactions (or mergers) or are intrinsic to the g alaxies, a natural consequence of the star formation process in primev al systems. Here I report the results of numerical simulations of prot ogalaxy evolution, which show that the gas-rich disk of a young galaxy becomes gravitationally unstable and fragments into massive clumps of sub-galactic size. Most of the stars are formed in these discrete clu mps, thereby providing a natural explanation for the peculiar morpholo gy of high-redshift galaxies. The dynamical evolution of these young s ystems is dominated by the clumps and ultimately leads to structures r esembling present-day galaxies, with a spheroidal bulge and an exponen tial disk I interpret the differences between the Hubble types of gala xies as resulting from different timescales of disk formation. Finally , the model provides a causal link between the emergence of quasar act ivity and the dynamical evolution of the host galaxy.