Galaxy Formation in the Lambda-Cold Dark Matter Cosmology

Abstract

In this thesis I explore the effects of the various physical processes behind galaxy formation and evolution in hierarchical cosmologies by using semi-analytical modelling. I use the Durham semi-analytical model GALFORM. I first test the GALFORM model predictions using observations from the Sloan Digital Sky Survey (SDSS). I use two different variants of the model, Baugh et al (2005), which assumes a top-heavy initial mass function (IMF) in starbursts and superwind feedback, and Bower et al (2006), which incorporates AGN feedback with a standard IMF. I compare the luminosity function, colours, sizes and morphology distributions of present-day galaxies in the models and with the SDSS. The Bower et al model better reproduces the shape of the luminosity function, the morphology-luminosity relation and the colour bimodality observed in the SDSS data. The Baugh et al model is much more successful at predicting galaxy sizes for late-type galaxies. Both models have problems with the sizes of early-type galaxies, which are predicted to be too large for low luminosities and too small for high luminosities compared to SDSS. I tested the impact on the model predictions of varying the prescriptions for supernova feedback, disk instabilities and galaxy mergers. In the second part of the thesis I explore the connection between two high redshift star-forming galaxy populations and present-day galaxies and their contribution to the star formation history. I built galaxy merger trees and followed the evolution and properties of submillimetre galaxies (SMGs) and Lyman-break galaxies (LBGs) using the Baugh et al (2005) model. The model predicts that the descendants of SMGs (S_{nu} > 5 mJy) have a median stellar mass of ~10e11/h solar masses, and that more than 70% of these descendants are bulge-dominated. More than 50% of present-day galaxies with stellar masses larger than 7 x 10e11/h solar masses are predicted to be descendants of such SMGs. Somewhat controversially, the stellar mass produced in the submillimetre phase contributes only 0.2% of the total present-day stellar mass, and 2% of the stellar mass of SMG descendants. The descendants of z=3 LBGs are predicted to have a median stellar mass equal to that of the Milky Way (M = 4 x 10e10/h solar masses), while the descendants of z=6 LBGs are predicted to have a larger median stellar mass (M = 10e11/h solar masses). The model predicts that only one in every 16 and one in every 50 Milky Way mass galaxies have a Lyman-break galaxy progenitor at z=3 and z=6 respectively