2010MNRAS.407..986R

We present the first non-local thermodynamic equilibrium (non-LTE), comoving frame molecular line calculations of a star-forming cluster simulated using smoothed particle hydrodynamics (SPH), from which we derive high-resolution synthetic observations. We have resampled a particle representation on to an adaptive mesh and self-consistently solved the equations of statistical equilibrium in the comoving frame, using torus, a three-dimensional adaptive mesh refined radiative transfer code. We verified the applicability of the code to the conditions of the SPH simulation by testing its output against other codes. We find that the level populations obtained for optically thick and thin scenarios closely match the ensemble average of the other codes. We have used the code to obtain non-LTE level populations of multiple molecular species throughout the cluster and have created three-dimensional velocity-resolved spatial maps of the emergent intensity. Line profiles of cores traced by N₂H⁺ (1-0) are compared to probes of low-density gas, ¹³CO (1-0) and C¹⁸O (1-0), surrounding the cores along the line of sight. The relative differences of the line centre velocities are shown to be small compared to the velocity dispersion, matching recent observations. We conclude that one cannot reject competitive accretion as a viable theory of star formation based on observed velocity profiles.