Three-dimensional molecular line transfer: A simulated star-forming region

TL;DR

This paper introduces a novel 3D non-LTE radiative transfer method applied to a simulated star-forming region, producing high-resolution synthetic molecular line observations that match real data and support competitive accretion models.

Contribution

It presents the first non-LTE, co-moving frame molecular line calculations for a star-forming cluster using SPH simulations and adaptive mesh refinement.

Findings

The code's output closely matches other radiative transfer codes for various optical depths.

Synthetic line profiles align with observed velocity dispersions in star-forming regions.

The results support the viability of competitive accretion in star formation theories.

Abstract

We present the first non-LTE, co-moving 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 onto an adaptive mesh and self-consistently solved the equations of statistical equilibrium in the co-moving frame, using TORUS, a three-dimensional adaptive mesh refined (AMR) radiative transfer (RT) 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.