A PIECEWISE PARABOLIC METHOD FOR COSMOLOGICAL HYDRODYNAMICS

We describe a hybrid scheme for cosmological simulations that incorporates a Lagrangean particle-mesh (PM) algorithm to follow the collisionless matter with the higher order accurate piecewise parabolic method (PPM) to solve the equations of gas dynamics. Both components interact through the gravitational potential, which requires the solution of Poisson's equation, here done by Fourier transforms. Due to the vast range of conditions that occur in cosmological flows (pressure differences of up to fourteen orders of magnitude), a number of additions and modifications to PPM were required to produce accurate results. These are described, as are a suite of cosmological tests.