The role of submillimetre galaxies in hierarchical galaxy formation

We study the role of submillimetre galaxies (SMGs) in the galaxy formation process in the Lambda cold dark matter cosmology. We use the Baugh et al. semi-analytical model, which matches the observed SMG number counts and redshift distribution by assuming a top-heavy initial mass function (IMF) in bursts triggered by galaxy mergers. We build galaxy merger trees and follow the evolution and properties of SMGs and their descendants. Our primary sample of model SMGs consists of galaxies which had 850 mu m fluxes brighter than 5 mJy at some redshift z > 1. Our model predicts that the present-day descendants of such SMGs cover a wide range of stellar masses similar to 1010-1012 h-1 M-circle dot, with a median similar to 1011h-1 M-circle dot, and that more than 70 per cent of these descendants are bulge-dominated. More than 50 per cent of present-day galaxies with stellar masses larger than 7 x 1011 h-1 M-circle dot are predicted to be descendants of such SMGs. We find that although SMGs make an important contribution to the total star formation rate at z similar to 2, the final stellar mass produced in the submillimetre phase contributes only 0.2 per cent of the total present-day stellar mass, and 2 per cent of the stellar mass of SMG descendants, in stark contrast to the popular picture in which the SMG phase marks the production of the bulk of the mass of present-day massive ellipticals.