Stellar halo of a galaxy preserves most of the information and assembly history and it could play a crucial role to understand the hierarchical structure formation. The nonlinear nature of the hierarchical structure formation and the wide range of physical processes involved, demand full physics computational models but covering full dynamic range is restricted by extremely high computational cost.
CoSANG (coupling semi-analytic and N-body galaxies) is a new approach in cosmological simulation, specifically designed for the stellar halo studies. In the first phase of CoSANG we have coupled a fast N-body model, Gadget 3 with a semi-analytic model, Sage. The semi-analytic model extracts baryonic information and CoSANG calculates the dynamical effects of baryons and feeds them back into the colissionless model. CoSANG is a self-consistent model and interacts with the simulation in all time-steps while it is running. We also use a comprehensive semi-analytic model which includes many physical processes with a possibility of exploring the parameter space more efficiently. Lower computational cost of CoSANG will let us to explore the structure formation in much higher resolution and resolve much smaller substructures. We study the inner structure of the halo and the subhalo distribution in the first phase. Using more realistic dynamics in CoSANG can provide more than dark matter only simulations using a newer, under development, particle tagging feature. In this phase CoSANG tags particles, according to their dynamical properties. The semi-analytic model provides more than full phase space information and we can paint particles and study metallicity, age, stellar mass of the stellar halo. This new approach could produce more realistic results in a higher resolution and could be calibrated by observations and hydrodynamic models.