Research interests:


 The distribution  and clustering of dark matter halos:

               According to current theory of structure formation, the matter content of the universe is dominated
               by cold dark matter (CDM). Because of  gravitational instability, perturbations in the CDM density
               distribution grow with time and form quasi-static clumps called dark matter halos. Luminous objects,
               such as galaxies and clusters of galaxies are assumed to form in the gravitational potential wells of
               CDM halos. Thus, a first step in understanding galaxy distribution in the universe is to understand
               how CDM halos are distributed in space. My interest here is to use both analytical models and   
               numerical simulations to understand how the distribution of dark matter halos is related to the underlying
               dark matter distribution, and how halo clustering depends on the intrinsic properties of dark halos.

 The structure of dark matter halos

               Cosmological numerical simulations have demonstrated that cold dark matter halos have structures
               that show  remarkable degree of regularity. My interest in this area is to understand the origin of such
               regularity: whether is it due to the formation history or is it a generic result of gravitational collapse?
               I am also interested in how to use gravitational lensing to probe dark matter halos and subhalos associated
               with galaxies and galaxy systems.

 Relation between galaxies and dark matter halos

               According to current theory of structure formation, galaxies are assumed to form in dark matter halos that
               are virialized clumps of dark matter. Since the properties of the dark halo population can be studied in great detail
               through numerical simulaions and analytical modeling, the first step in understanding how galaxies form in the
               cosmic density field is to establish the relationship between galaxies and dark matter halos. Two methods are
               currently used to establish the relationship between galaxies  and dark matter  halos. One is based the conditional
               luminosity function model, which links galaxies and dark matter halos by matching the number density and clustering
               properties of galaxies with those of dark matter halos in the current CDM model. The second is based on galaxy systems
               identified from large redshift surveys of galaxies.  I am particularly interested in studying the implications of  the
               galaxy/dark halo relationship for galaxy formation and evolution using analytical and semi-analytical models
               and numerical simulations.

 Large-scale clustering of galaxies

               With the advent of large galaxy redshift surveys, such as the Sloan Digital Sky Survey and the 2-degree Galaxy Redshift
               Survey, analyses of galaxy clustering can not only be made for the general galaxy population, but also for galaxies of
               different properties, such as luminosity, color, morphological type etc. My interest here is to develop statistical methods
               to characterize  the clustering  properties of galaxies and to understand  how the results can constrain galaxy formation
               and evolution.

 Galaxy formation and evolution

               Here my interest is in the formation of galaxy disks in dark matter halos,  what determine the luminosity, size,
               and scaling relations of spiral galaxies, and how the interactions between dark matter and baryonic matter affect the rotation
               curves of disk galaxies, and how star formation efficiency in a halo is affected by star formation feedback as well large-scale
               environmental effects. I am also interested in how to use quasar absorption line systems to probe the gas structure in protogalaxies
               and in the intergalactic medium.