The Formation Of Blue Cluster In Local Universe

This dissertation combines Sloan Digital Sky Survey(SDSS)DR7 group catalog with Semi-Analytical Models(SAM)of galaxy formation to explore physical properties and large scale structures of clusters that have higher fraction of star-forming galaxies(blue fraction)in local Universe,and to find the differences from clusters which have lower blue fraction.This dissertation also combines the SAM that was established by Kang et al with the dark matter merger trees produced by Millennium Simulation(MS)to explore the performance of this model in simulating large-scale cosmology by com-paring with observational data.In chapter 1,I introduce cold dark matter model with dark energy(?CDM)and some basic observational facts of galaxies.These observational facts would construct a figure of cosmology and galaxies evolution.In chapter 2,I introduce the framework of L-Galaxies and Kang et al that are rep-resentatives of SAM,which include dark matter halo merger trees and main physical processes of galaxies formation and evolution.In chapter 3,I review previous works about blue fraction of clusters in the local Universe,and introduce the method used in this work to find galaxy clusters.In chapter 4,I present the main results of this dissertation.Overall,we find blue fraction decreases as increase of cluster halo mass and of formation time.We find four clusters whose blue fraction is larger than 0.5 in observation,while one of them is effected by large scale structures,and this cluster is at the intersection of filaments that seems to be merging.We split clusters into blue cluster and red clusters,and find that the age of blue clusters is younger than red clusters.We also find that blue fraction of galaxies within projected 2Rvir from cluster center are lower in blue clusters.In L-Galaxies,we split cluster member galaxies into central galaxy and satellite galaxies,then we find that satellite galaxies of blue clusters have more cold gas than those in red.We also find that the infalling time of satellites in blue clusters are later,which implies that formation of blue clusters is mainly governed by newly accreted blue satellites that still have cold gas.In chapter 5,I focus on the results using the SAM by Kang et al with the merger trees from the MS,we find that the stellar mass functions produced by model are consis-tent with observations at different redshifts.The model could also reproduce luminosity functions in different bands.The star formation rate function(SFRF)predicted by the model could fit the data at z<1,but the predictions are lower than observations at high redshift.The quench fraction and stellar mass relation produced by the model have distinct difference from observations at z=0.The cold gas fraction predicted by the model in low mass galaxies is larger than observations at z=0.These results suggest that this model could be further improved.In chapter 6,I summarize our current work and give prospect for future work.