High Redshift Galaxy Populations and their Descendants

We study model predictions for the abundance and clustering of high-redshift galaxies, and for the properties of their descendants. We focus on three high-redshift populations: Lyman break galaxies at z ∼ 3 (LBGs), optically selected star-forming galaxies at z ∼ 2 (BXs), and distant red galaxies at z ∼ 2 (DRGs). We select model galaxies from mock catalogues using the observationally defined colour and magnitude criteria. With plausible dust assumptions, our galaxy formation model can simultaneously reproduce the abundances, the redshift distributions and the clustering of all three observed populations. The star formation rates (SFRs) of model LBGs and BXs are lower than those quoted for the real samples, reflecting different initial mass functions and scatter in model dust properties. About 85% of model galaxies selected as DRGs are star-forming, with SFRs ranging up to ∼ 102M⊙/yr. Model LBGs, BXs and DRGs together account for less than half of all star formation over the range 1.5 < z < 3.2; many massive, star-forming galaxies are predicted to be too heavily obscured to appear in these populations. Model BXs have metallicities which agree roughly with observation, but model LBGs are only slightly more metal-poor, in disagreement with recent observational results. The model galaxies are predominantly disk-dominated. Stellar masses for LBGs and BXs are typically ∼ 109.9M⊙, and for DRGs are ∼ 10 10.7M⊙. Only about 30% of model galaxies with M > 1011M⊙ are classified as LBGs or BXs at the relevant redshifts, while 65% are classified as DRGs. Almost all model LBGs and BXs are the central galaxies of their dark halos, but about a quarter of DRGs are satellites. Half of all LBG descendants at z = 2 would be identified as BX’s, but very few as DRGs. Clustering increases with decreasing redshift for descendants of all three populations, becoming stronger than that of L galaxies by z = 0, when many have become satellite galaxies and their mean stellar mass has increased by a factor of 10 for LBGs and BXs, and by a factor of 3 for DRGs. This growth is dominated by star formation until z ∼ 1 and thereafter by mergers. Merging is predicted to be more important for LBG and DRG descendants than for BX descendants. Most LBGs and DRGs end up as red ellipticals, while BXs have a more varied fate. 99% of local galaxies with M∗ > 10 11.5M⊙ are predicted to have at least one LBG/BX/DRG progenitor, and over 70% above 1011M⊙