COLLAPSE OF POPULATION III OBJECTS INDUCED BY COLD COLLISIONLESS DARK MATTER

We study the formation of Population III objects that can be formed by cold collisionless dark matter. We assume that at the beginning of the recombination era there exist perturbations only in the dark matter. We take into account photon drag, photon cooling, recombination, photoionization, collisional ionization, Lyman-alpha cooling, and the formation and cooling of hydrogen molecules in the baryonic matter. We find, for example, that for a universe that contains a greater quantity of dark matter (i.e., a larger OMEGA-d, the ratio of the present density of dark matter to the critical density), the collapse occurs faster for a given perturbed dark matter mass, M(d), but a smaller quantity of baryonic mass is carried with it. For a given universe (i.e., OMEGA-b and OMEGA-d given) we find that for larger M(d) a greater fraction of baryonic matter, M(bc)/M(bi), follows the dark matter collapse, where M(bi) is the baryonic mass in the perturbed dark matter region at the beginning of the recombination era and M(bc) is the baryonic mass in the perturbed dark matter region after turnaround at the time of collapse. We previously showed that the minimum mass to collapse from the recombination era without dark matter was approximately 10(4) M.; we show here that our calculations indicate that with dark matter the minimum mass is reduced to approximately 10(3) M. if virialization occurs at approximately 0.01r(ta); and is approximately 10(4) M. if virialization occurs at approximately 0.5 r(ta), where r(ta) is the turnaround radius.