1. Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-77, Japan

Correspondence to: Masafumi Noguchi¹ Correspondence and requests for materials should be addressed to M.N. (e-mail address: Email: noguchi@astroa.astr.tohoku.ac.jp).

Abstract

Many high-redshift galaxies have peculiar morphologies and photometric properties^{1, 2, 3, 4, 5}. It is not clear whether these peculiarities originate in galaxy–galaxy interactions (or mergers) or are intrinsic to the galaxies, a natural consequence of the star formation process in primeval systems. Here I report the results of numerical simulations of protogalaxy 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 clumps, thereby providing a natural explanation for the peculiar morphology of high-redshift galaxies. The dynamical evolution of these young systems is dominated by the clumps and ultimately leads to structures resembling present-day galaxies, with a spheroidal bulge and an exponential disk. I interpret the differences between the Hubble types of galaxies as resulting from different timescales of disk formation. Finally, the model provides a causal link between the emergence of quasar activity and the dynamical evolution of the host galaxy.

1. Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-77, Japan

Correspondence to: Masafumi Noguchi¹ Correspondence and requests for materials should be addressed to M.N. (e-mail address: Email: noguchi@astroa.astr.tohoku.ac.jp).