Direct N-Body Simulation with Graphic Processing Units : Dynamical Evolution of Galaxy Cluster Collisions and a Dynamaical Fossil in Ursa Minor Dwarf Spheroidal Galaxy

In this paper, we discuss the density distribution of DM halo. We want to understand that if the core size of the dark matter halo will change with different initial conditions of merging. We use NFW model with two param- eters to describe the DM halo, and these two parameters are concentration and the mass of the total halo. Concentration is the ratio between the size of DM halo and the core. In order to speed up the computing time, our lab use the GPU parallel computing process to simulate, thus it is 300 times faster than CPU code( [1]Chen 2007). The merging simulation is only consider the grav- itational interaction. We let the halos merge to others with different relative velocities and also the free falling case. The result shows that when we let the DM halos free fall to each other, the concentration of the new DM halo will increase 8%. On the other hand, if the relative kinetic energy increase 30%, the total mass of the new halo will decrease 8% and the concentration also decrease 5
On the other hand, we try to simulate the star clump underlie in the Ursa Minor dwarf spheroidal. We try to use our BEC dark matter, ψDM, to explain the possible orbits of the clump,which are all on the sky surface or with a small radius velocity 1km/s. We also give the upper limit of velocity of the clump that the halo can not move faster than 6km/s on the sky surface.