High-redshift Galaxies Into Groups And Evolution

First, we investigate the feasibility of determining the pairwise velocity dispersion (PVD) for Lyman Break Galaxies, and of using this quantity as a discriminator among theoretical models. We find that within a given cosmological model different schemes of galaxy formation lead to significant changes of the PVD. We propose a simple phenomological model for the formation of Lyman break galaxies, determined by the formation interval parameter z and the halo mass threshold Mh. With a reasonable choice for these two parameters, our model predicts an occupation number distribution of galaxies in halos which agrees very well with the predictions of semi-analytical models. We also consider a range of galaxy formation models by adjusting the two model parameters. We find that model LBGs can have the same Two Point Correlation Funtion (TPCF) over the range of observable separations even though the cosmology and/or galaxy formation model are different. Moreover, with similar galaxy formation models, different cosmologies can result in both the same TPCF and the same PVD. However, with the same cosmology, different galaxy formation model may show quite different PVDs even though the TPCF is the same. Our test with mock samples shows furthermore that one can discriminate among such models already with currently available observational samples (if the measurement error of the redshift is negligible) which have a typical error of 80kms-1. The error will be reduced by a factor of 2 if the samples are increased four times. We also show that an errroneous assumption about the geometry of the universe and different infall models only slightly change the results. Therefore the PVD will become another promising statistic to test galaxy formation models with redshift samples of LBGs.Then, we analyse in detail the mass-accretion histories and structural properties of dark haloes in high-resolution N-body simulations. We model the density distribution in individual haloes using the NFW profile. For a given halo, there is a tight correlation between its inner scale radius rs and the mass within it. Ms, for all its main progenitors, which is the basic reason why halo structural properties are closely related to their mass-accretion histories. This correlation can be used to predict the structural properties of a dark halo at any time in its history. Since the scaling relation we found is intrinsic, this application is independant of how we define haloes, when we do observation and which cosmogony we choose. The build-up of dark haloes in CDM models generally consists of an early phase of fast accretion [where the halo mass Mh increases with time much faster than the expansion rate of the universe] and a late phase of slow accretion [where Mh increases with time approximately the same as the expansion rate]. These two phases are separated at a time when the halo concentration parameter c ~ 5 and the binding energy of the halo is approximately equal to that of a singular isothermal sphere with the same circular velocity. Haloes in the two accretion phases show systematically different properties, for example, the circular velocity vh increases rapidly withtime and approximately equals the inner circular velocity vs in the fast accretion phase, but remain almost constant and less than vs in the slow accretion phase: the inner properties of a halo, such as rs and Ms increase rapidly with time in the fast accretion phase but change only slowly in the slow accretion phase: the halo concentration changes slow in the fast accretion phase, but increases rapidly with the Hubble expansion in the slow accretion phase. The inner structure and potential well associated with a halo is built up mainly in the fast accretion phase, while a large amount of mass can be accreted in the slow accretion phase without changing significantly the inner properties and the potential well. Our results are much helpful for us to understand the building-up mechanism of the universal density profile, galaxy formation and high redshift Tully-Fisher relation...