SUPERMASSIVE BLACK HOLE FORMATION AT HIGH REDSHIFTS THROUGH A PRIMORDIAL MAGNETIC FIELD

It has been proposed that primordial gas in early dark matter halos, with virial temperatures T-vir greater than or similar to 10(4) K, can avoid fragmentation and undergo rapid collapse, possibly resulting in a supermassive black hole. This requires the gas to avoid cooling and to remain at temperatures near T similar to 10(4) K. We show that this condition can be satisfied in the presence of a sufficiently strong primordial magnetic field, which heats the collapsing gas via ambipolar diffusion. If the field has a strength above vertical bar B vertical bar greater than or similar to 3.6 (comoving) nG, the collapsing gas is kept warm (T similar to 10(4) K) until it reaches the critical density n(crit) approximate to 10(3) cm(-3) at which the rotovibrational states of H-2 approach local thermodynamic equilibrium. H-2 cooling then remains inefficient and the gas temperature stays near similar to 10(4) K, even as it continues to collapse at higher densities. The critical magnetic field strength required to permanently suppress H-2 cooling is somewhat higher than the upper limit of similar to 2 nG from the cosmic microwave background. However, it can be realized in the rare greater than or similar to(2-3)sigma regions of the spatially fluctuating B field; these regions contain a sufficient number of halos to account for z approximate to 6 quasar black holes.