On The Gas Temperature of Molecular Cloud Cores

TL;DR

This paper examines the factors influencing the temperature profiles of dense molecular cloud cores, highlighting the importance of radiative transfer effects and chemical depletion processes in understanding core conditions.

Contribution

It identifies key uncertainties affecting core temperature predictions and emphasizes the significance of non-local radiative transfer in modeling interstellar cloud cores.

Findings

Variations in gas abundances and grain sizes affect temperature by 1-2°C.

Non-local radiative transfer significantly influences temperature profiles.

Temperature uncertainties impact molecular depletion and core chemistry.

Abstract

We investigate the uncertainties affecting the temperature profiles of dense cores of interstellar clouds. In regions shielded from external ultraviolet radiation, the problem is reduced to the balance between cosmic ray heating, line cooling, and the coupling between gas and dust. We show that variations in the gas phase abundances, the grain size distribution, and the velocity field can each change the predicted core temperatures by one or two degrees. We emphasize the role of non-local radiative transfer effects that often are not taken into account, for example, when modelling the core chemistry. These include the radiative coupling between regions of different temperature and the enhanced line cooling near the cloud surface. The uncertainty of the temperature profiles does not necessarily translate to a significant error in the column density derived from observations. However, depletion processes are very temperature sensitive and a two degree difference can mean that a given molecule no longer traces the physical conditions in the core centre.