Simulating the Magnetic Field in the Local Supercluster

We construct the first realistic map of deflections of ultra-high energy cosmic rays by extragalactic magnetic fields, using a magneto-hydrodynamical simulation of cosmic structure formation that reproduces the positions of known galaxy clusters in the local universe. Large deflection angles occur in cluster regions, which however cover only an insignificant fraction of the sky. More typical deflections of order ∼ 1 arcdeg are caused by crossings of filaments. For protons with energies E ≥ 4×10^{19} eV, deflections do not exceed a few degrees over most of the sky up to a propagation distance of 500 Mpc. Given that the field strength of our simulated intergalactic magnetic field forms a plausible upper limit, we conclude that charged particle astronomy is in principle possible.