Molecular processes and gravitational collapse in intergalactic shocks

The thermal and gravitational consequences of molecular formation behind 20-200 km/s intergalactic shocks produced by explosions at large redshift or by cloud collisions during infall into gravitational potential wells are examined. It is shown that significant abundances of H2/H, roughly 0.001, can be formed behind the shocks in the primordial intergalactic medium (IGM), significantly larger than those needed to radiate away the energy of gravitational collapse. Molecular cooling therefore solves the problem of obtaining gravitationally bound fragments from explosions in the primordial IGM. The sensitivity of the molecular formation to the preshock density, shock velocity, and ambient quasar radiation field is discussed.