Gas-dynamical processes in the theory of galaxy formation

The author has solved the hydrodynamical conservation equations, along with the rate equations for nonequilibrium ionization, recombination, and molecule formation and the equation of radiative transfer, for steady state shocks in a gas of primordial composition. His calculation self-consistently includes the effects of the diffuse postshock emission as well as a possible external radiation flux on the postshock flow. This study shows that the shocked gas cools faster than it can recombined and, as a result, is able to form an H2 concentration as high as 10-3 via the formation of H- and H2+ intermediaries due to the enhanced nonequilibrium ionization fraction at 104 K. He applies the shock calculation to explore the hypothesis that globular clusters were formed by gravitational instability behind radiative shocks inside protogalaxies. The results indicate that, in the absence of a strong external source of UV radiation, the shock-heated gas radiatively cools below 104 K as a result of H2 formation and cooling to ∼102 K before the globular cluster mass can be imprinted on the gas by Jeans instability. In this case the suggestion of globular cluster formation behind such protogalactic shocks fails. He has developed a 3D hydrodynamical N-body code, the merger of a Smoothed Particle Hydrodynamics code with a hierarchical N-body Particle-Mesh code. He has applied the code to the problem of pancake formation and compared our results to previous detailed, 1D, planar, numerical hydrodynamic simulations