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We run "cosmological" simulations (where the volume is an appreciable fraction of the observable universe) with the new code AREPO. This is a second-order finite volume method that solves the Euler equations with the Godunov approach for numerical fluxes with the well-known MUSCL-Hancock scheme. AREPO discretizes space with an unstructured mesh corresponding to the Voronoi tessellation of 3D space. This arises from a set of mesh-generating points whose motion we tie to the motion of the hydrodynamical flow, giving the scheme a quasi-Lagrangian and automatically adaptive character.

My interest is the nature of gas flows as matter is accreted on to dark matter halos (not shown, but represented here by the sphere). This interactive visualization renders gas fluid quantities such as temperature, density, and entropy at one instant in time for a small region of space surrounding one halo. It shows four strong filamentary gas structures which are connected to a "cold accretion mode" of galaxy growth. We study this mode, its nature and its importance, particularly in comparison of AREPO results to previous work which has largely been done with the smoothed particle hydrodynamics (SPH) technique.

Dylan Nelson (Grad Student @ Harvard)