Molecular Emission Line Formation in Prestellar Cores

TL;DR

This paper explores how molecular lines form in prestellar cores using radiative transfer simulations, providing tools and insights for interpreting observed molecular spectra in star-forming regions.

Contribution

It introduces a detailed scheme for understanding emission line formation, including a contribution chart and analysis of physical effects on line profiles in uniform and non-uniform cores.

Findings

Line profiles depend on density, temperature, and molecular column density.

The contribution chart helps identify cloud regions contributing to specific spectral features.

Physical factors interact cooperatively to shape molecular emission characteristics.

Abstract

We investigate general aspects of molecular line formation under conditions which are typical of prestellar cores. Focusing on simple linear molecules, we study formation of their rotational lines by radiative transfer simulations. We present a thermalization diagram to show the effects of collisions and radiation on the level excitation. We construct a detailed scheme (contribution chart) to illustrate the formation of emission line profiles. This chart can be used as an efficient tool to identify which parts of the cloud contribute to a specific line profile. We show how molecular line characteristics for uniform model clouds depend on hydrogen density, molecular column density, and kinetic temperature. The results are presented in a 2D plane to illustrate cooperative effects of the physical factors. We also use a core model with a non-uniform density distribution and chemical stratification to study the effects of cloud contraction and rotation on spectral line maps. We discuss the main issues that should be taken into account when dealing with interpretation and simulation of observed molecular lines.