The role of ambipolar diffusion in the fragmentation of condensations of the primordial gas

We consider the evolution and fragmentation of cylindrical filaments of the primordial gas. The filaments are formed following shock compression and heating, occurring subsequent to the gravitational collapse of condensations of the primordial medium. The role of ambipolar diffusion is studied, under circumstances where the magnetic energy density is comparable with the thermal energy density in the filaments, prior to their collapse. It is shown that ambipolar diffusion reduces the masses of the fragments by about an order of magnitude when the fractional ionization of the gas n (H+ )/n (H) is of the order of 10(-8) or less. Under these conditions, ambipolar diffusion is sufficiently rapid for the fragment masses to be similar to those computed neglecting the magnetic field. Attention is drawn to the importance of the H+ (H-2 , hnu) H+ (3) reaction, whose rate coefficient is very uncertain.