The nature of high-redshift galaxies

Using semi-analytic models of galaxy formation, we investigate the properti es of z similar to 3 galaxies and compare them with the observed population of Lyman-break galaxies (LBGs). In addition to the usual quiescent mode of star formation, we introduce a physical model for starbursts triggered by galaxy-galaxy interactions. We find that with the merger rate that arises n aturally in the CDM-based merging hierarchy, a significant fraction of brig ht galaxies identified at high redshift (z greater than or similar to 2) ar e likely to be low-mass, bursting satellite galaxies. The abundance of LBGs as a function of redshift and the luminosity function of LBGs both appear to be in better agreement with the data when the starburst mode is included , especially when the effects of dust are considered. The objects that we i dentify as LBGs have observable properties including low velocity dispersio ns that are in good agreement with the available data. In this "Bursting Sa tellite" scenario, quiescent star formation at z greater than or similar to 2 is relatively inefficient and most of the observed LBGs are starbursts t riggered by satellite mergers within massive halos. In high-resolution N-bo dy simulations, we find that the most massive dark matter halos cluster at redshift z similar to 3 much as the Lyman-break galaxies (LBGs) are observe d to do. This is true for both the Omega = 1 CHDM model and low-Omega Lambd a CDM and OCDM models, all of which have fluctuation power spectra P(k) con sistent with the distribution of low-redshift galaxies. The Bursting Satell ite scenario can resolve the apparent paradox of LBGs that cluster like mas sive dark matter halos but have narrow linewidths and small stellar masses. (C) 1998 Elsevier Science B.V. All rights reserved.