Abstract
A detailed, numerical hydrodynamical calculation is presented of the growth of a combined neutrino-baryon pancake in a postrecombination Friedmann universe dominated by massive neutrinos. The purpose of this calculation is to test the hypothesis that galaxies can form within the adiabatic, or so-called pancake, scenario, if the universe is neutrino-dominated. First, we present the results of a detailed, numerical, three-dimensional collisionless particle simulation which demonstrates that one-dimensional, plane-symmetric pancakes are a generic form for the structure which develops from a general, three-dimensional perturbation spectrum with a short-wavelength cutoff. The evolution of an individual pancake is then calculated by numerically solving the hydrodynamical conservation equations for the baryonic fluid, together with the Poisson equation for the combined neutrino-baryon gravitational potential and the Vlasov equation for the collisionless neutrinos, all in a homogeneous, isotropically expanding universe described by the Robertson-Walker metric. The effects of ionization, recombination, and radiative cooling are explicitly included.
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