COLLAPSE OF ROTATING PRIMORDIAL CLOUDS AND CRITERIA FOR FRAGMENTATION

Abstract

The collapse of the rotating clouds is investigated using three-dimensional self-gravitating hydrodynamical simulations. We take into account of the detailed nonequilibrium chemical reactions for primordial gas that consists of pure hydrogen. The property of the collapse and condition of the fragmentation is compared with that of isothermal clouds. It is shown that the geometrical flatness of the central region of the disk is a good indicator to predict whether the clouds fragment or not. If the flatness is greater than the critical value 〜 4π, a cloud fragments into filaments and blobs. On the other hand, if the flatness is smaller than the critical value, the fragmentation is not expected before the central core formation even if the cooling is efficient and the total mass becomes much greater than the local Jeans mass at the center. For the primordial gas, the flatness is increasing function of the mass. The critical mass is found to be 3 × 10^6M_⊙. If the initial cloud mass is smaller than this critical value, fragmentation before the central core formation is not expected. For the typically estimated first collapsing cosmological baryonic object, M≲10^6M_⊙, the central core formation is expected and it will have a significant effect to the later evolution of the whole system.