| Description |
Observing galaxy clustering is an effective way to gain knowledge of galaxy formation and evolution and to constrain cosmology. Cosmology determines halo population and clustering (bias), and galaxy-halo relation connects halo clustering to galaxy clustering. However, traditional halobased models of galaxy clustering only consider the halo mass dependence and ignore any effect caused by halo assembly history, which may cause systematics in constraining the galaxy-halo relation and cosmology. My work is focused on investigating halo and galaxy assembly bias, aiming at providing insights to improve models of galaxy clustering. First, the joint dependence of halo bias on halo mass and other halo assembly variables is investigated. It is found that halo bias increases outward from a global minimum on the plane of halo mass and one assembly variable. Based on the joint dependence, halo assembly bias is unlikely to be fully absorbed by any combination of halo variables. Furthermore, dependence of halo bias on one assembly variable can be independent from that on another one even if the two variables are correlated. Additionally, assembly effects on halo kinematics are shown to correlate with those of spatial clustering. Another component in halo models, the galaxy-halo relation, is studied with a hydrodynamic simulation. The correlations between a set of galaxy properties and halo properties are analyzed. Then a simple model is developed to relate galaxy assembly bias and halo assembly bias through the correlation coefficient between halo and galaxy properties, which provides an effective prescription to incorporate galaxy assembly bias into halo models of galaxy clustering. Finally, a specific aspect of the galaxy-halo relation, the distribution of galaxy luminosity and color at a given halo mass (i.e. the conditional color magnitude distribution, CCMD) in galaxy formation models is investigated. In a semi-analytical galaxy formation model, the CCMD of central galaxies is found to be comprised of a red and a blue population, in a pattern consistent with that inferred from modeling the observed luminosity and color-dependent galaxy clustering. An attempt has been made to map galaxy color and luminosity onto halo assembly variables to figure out the physical origin of the two populations. |
