The Formation of Stellar Clusters: Gaussian Cloud Conditions I

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 which peaks approximately at the average Jeans mass of the system. Scaled to physical conditions typical for star-forming molecular clouds, the mass function is in good agreement with the IMF of multiple stellar systems. 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.