Fragmentation of Molecular Clouds II: The Standard Model
Abstract
The isothermal dynamical evolution of a clumpy and turbulent molecular cloud region and its fragmentation into a protostellar cluster is investigated numerically. The effect of different initial density and velocity distributions, generated from different realizations of a Gaussian random field with power spectrum P(k)~k^{-2} is investigated. As a result of the interplay between gas pressure and gravitational forces, a quasi-equilibrium clump mass spectrum emerges with a power-law distribution dN/dM ~ M^{-1.5}, independent of the initial conditions. Being part of a complex network of filaments, individual clumps are elongated, centrally condensed objects with 2:1 to 4:1 axis ratios with outer r^{-2} density distributions. Dense, Jeans-unstable gas clumps collapse and form protostellar cores which evolve through competitive accretion and N-body interactions with other cores. In contrast to the clumps, the core mass spectrum is best described by a log-normal distribution with a peak and a width that is in excellent agreement with observations of multiple stellar systems if one adoptes a core star formation efficiency of order 15%. The final dynamical state of the newly formed stellar cluster closely resembles observed young stellar clusters. It has a core/halo structure which is typical for collision dominated N-body systems. The 2-point correlation function of the spatial stellar distribution can be described by two power-laws with a break in the slope at the transition point from the binary to the large-scale clustering regime. The protostellar cluster is marginally bound and would be easily disrupted, if the conversion of cores into stars is inefficient.Keywords
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