MOMENTUM-TRANSFER BY AN INTERNAL SOURCE OF IONIZING-RADIATION - AN IMPORTANT FEEDBACK PROCESS DURING GALAXY FORMATION

The role of momentum transfer ('radiation pressure') due to an internal source of ionizing radiation for the formation of baryonic structures is investigated. Fully ionized, self-gravitating gaseous objects can be radiation-pressure-supported on a characteristic length scale D-rp similar to 100 pc-3 kpc. On smaller scales momentum transfer due to ionizing radiation will be the dominant force, and for spherical collapsing objects of mass less than or similar to 10(10) M. a complete bounce is possible. A population of massive stars and/or accretion on to a central compact object are natural sources of ionizing radiation in newly forming baryonic structures. Radiation pressure is therefore likely to play an important role in the dynamical and thermal evolution of the intergalactic medium and the mass-to-light ratios of small galaxies. The effect will be especially important for hierarchical cosmogonies where galactic structures build up by merging of smaller objects. Radiation pressure due to ionizing radiation might, furthermore, be responsible for substructures of size D-rp in the stellar component of large galaxies.