DENSE CORE FORMATION AND COLLAPSE IN GIANT MOLECULAR CLOUDS

In this thesis we present a unified model for dense core formation and collapse within post-shock dense layers inside giant molecular clouds. Supersonic converging flows col-lide to compress low density gas to high density clumps, inside which gravitational col-lapse can happen. We consider both spherically symmetric and planar converging flows, and run models with inflow Mach numberM ≡ v/cs = 1.1−9 to investigate the relation between core properties and the bulk velocity dispersion of the mother cloud. Four stages of protostar formation are identified: core building, core collapse, envelope infall, and late accretion. The core building stage takes 10 times as long as core collapse, which lasts a few ×105yr, consistent with observed prestellar core lifetimes. We find that the density profiles of cores during collapse can be fitted by Bonnor-Ebert sphere profiles, and that the density and velocity profiles approach the Larson-Penston solution at the core collapse instant. Core shapes change from oblate to prolate as they evolve. Cores with masses varying by three orders of magnitude ( ∼ 0.05−50 M) are identified in our high-M simulations, and a much smaller mass range for models having lowM. The me-dian core mass versusM lies between the minimum mass that can collapse in late time