Hydromagnetic waves in an expanding universe – cosmological MHD code tests using analytic solutions

ABSTRACT We describe how analytic solutions for linear hydromagnetic waves can be used testing cosmological magnetohydrodynamic (MHD) codes. start from the comoving MHD equations and derive amplitude evolution of in a matter-dominated, flat Einstein-de-Sitter (EdS) universe. The considered are comoving, linearly polarized Alfvén magnetosonic (fast) modified by self-gravity. solution compressible is found general adiabatic index we consider limits hydrodynamics without self-gravity addition to full solution. In these solutions, linearized solved numerically Λ cold dark matter cosmology. use numeric compare with results obtained using code arepo find good agreement when sufficient number grid points. interpret numerical damping clearly evident simulations few points further deriving wave including physical Navier–Stokes viscosity. A comparison between theory reveals that dissipation described viscosity coefficient ηnum ∝ a−5/2, where scale factor. envision our examples could useful developing new or regression existing