Cosmic-ray heating of molecular cloud cores

TL;DR

This paper investigates how cosmic rays influence the heating and chemical structure of dense molecular cloud cores, using detailed observations of the L1544 core to estimate a lower cosmic-ray ionization rate than in diffuse clouds.

Contribution

It demonstrates that high-resolution temperature data can constrain cosmic-ray ionization rates in prestellar cores, revealing lower rates than in the diffuse interstellar medium.

Findings

L1544's thermal and chemical data support a cosmic-ray ionization rate of ~10^{-17} s^{-1}

The method can be applied to molecular clouds in other galaxies

Cosmic-ray heating significantly impacts core chemistry and temperature structure

Abstract

Cosmic rays are an important source of heating in the interstellar medium, in particular in dense molecular cloud cores shielded from the external ultraviolet radiation field. The limits placed on the cosmic-ray ionization rate from measurements of the gas temperature in dense clouds are unaffected by the uncertainties associated to the traditional methods based on the analysis of molecular abundances. However, high-resolution data are required to determine with sufficient accuracy the spatial temperature distribution within prestellar cores. In this contribution we illustrate in detail the case of the well-studied prestellar core L1544, showing that both its thermal structure and chemical composition are consistent with a cosmic ray ionization rate of $\sim 10^{-17}$~s$^{-1}$, significantly smaller than the value measured in the diffuse interstellar medium. We also briefly discuss possible applications of this method to molecular clouds of other galaxies