Feedback from galaxy formation: Production and photodissociation of primordial H-2

We use one-dimensional radiative transfer simulations to study the evolutio n of H-2 gas-phase (H- catalyzed) formation and photodissociation regions i n the primordial universe. We find a new positive feedback mechanism capabl e of producing shells of H-2 in the intergalactic medium (IGM), which are o ptically thick in some Lyman-Werner bands. While these shells exist, this f eedback effect is important in reducing the H-2 dissociating background flu x and the size of photodissociation spheres around each luminous object. Th e maximum background opacity of the IGM in the H-2 Lyman-Werner bands is ta u (H 2)approximate to1-2 for a relic molecular fraction chi (H 2)=2x10-6, a bout 6 times greater than that found by Haiman, Abel, & Rees. Therefore, th e relic molecular hydrogen can decrease the photodissociation rate by about an order of magnitude. The problem is relevant to the formation of small p rimordial galaxies with masses M(DM)less than or similar to 10(8) M-circle dot that rely on molecular hydrogen cooling to collapse. Alternatively, the universe may have remained dark for several hundred million years after th e birth of the first stars, until galaxies with virial temperature T(vir)gr eater than or similar to 10(4) K formed.