Investigating the clustering of halos and galaxies helps us learn about cosmology and galaxy formation physics. The clustering of dark matter halos is found to depend on not only halo mass but also halo properties related to their formation history or environment, which is called halo assembly bias. If galaxy properties depend on halo assembly properties in addition to halo mass, the clustering of galaxies would show the so-called galaxy assembly bias. Halo and galaxy assembly bias affects how accurate galaxy clustering can be modeled, and may lead to systematics in constraining cosmology and galaxy formation from galaxy clustering. In this talk, I will first review previous study of halo assembly bias and present an investigation of the joint dependence of halo bias on halo mass and halo assembly variables based on N-body simulations. Then I will discuss the possibility of constructing a combination of halo variables to absorb the halo assembly bias effect. Finally, I will present galaxy assembly bias of central galaxies in a hydrodynamic galaxy formation simulation and propose a simple way to incorporate the effect into the halo model of galaxy clustering.
Speaker:Xiaoju Xu, Univ. of Utah
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