A PIECEWISE PARABOLIC METHOD FOR COSMOLOGICAL HYDRODYNAMICS

We describe a hybrid scheme for cosmological simulations that incorpor ates a Lagrangean particle-mesh (PM) algorithm to follow the collision less 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 P oisson's equation, here done by Fourier transforms. Due to the vast ra nge of conditions that occur in cosmological flows (pressure differenc es of up to fourteen orders of magnitude), a number of additions and m odifications to PPM were required to produce accurate results. These a re described, as are a suite of cosmological tests.