Abstract
Aims. We intend to derive statistical properties of stochastic gas motion inside the dense, low-mass star-forming molecular cores that are traced by NH3(1, 1) and (2, 2) emission lines.
Methods. We use the spatial two-point autocorrelation (ACF) and structure functions calculated from maps of the radial velocity fields.
Results. The observed ammonia cores are characterized by complex intrinsic motions of stochastic nature. The measured kinetic temperature ranges between 8.8 K and 15.1 K. From NH3 excitation temperatures of 3.5-7.3 K, we determine H-2 densities with typical values of n(H2) similar to (1-6) x 10(4) cm(-3). The ammonia abundance, X = [NH3]/[H-2], varies from 2 x 10(-8) to 1.5 x 10(-7). We find oscillating ACFs, which eventually decay to zero with increasing lags on scales of 0.04 less than or similar to l less than or similar to 0.5 pc. The current paradigm supposes that the star-formation process is controlled by the interplay between gravitation and turbulence with the latter preventing molecular cores from a rapid collapse due to their own gravity. Thus, oscillating ACFs may indicate a damping of the developed turbulent flows surrounding the dense but less turbulent core, a transition to dominating gravitational forces and, hence, to gravitational collapse.