Nuclear de-excitation line emissions from giant molecular clouds

TL;DR

This paper analytically models cosmic ray propagation in giant molecular clouds, predicting nuclear de-excitation line emissions and ionization rates, and suggests future MeV observations can probe low-energy CR densities.

Contribution

It introduces an analytical framework for CR distribution in GMCs under various diffusion scenarios and links it to observable nuclear line emissions and ionization rates.

Findings

Future MeV observations can measure low-energy CR densities.

Different CR diffusion models produce distinct nuclear line emission signatures.

CR interactions significantly influence GMC heating and star formation processes.

Abstract

Understanding how cosmic rays (CRs) propagate within the giant molecular clouds (GMCs) is critical for studying the dynamics and chemical processes inside the clouds. The flux of low-energy CRs inside the dense cores of GMCs strongly affects the heating and ionization of the gases and further influences the star-forming process. We analytically calculated the CR distribution inside GMCs assuming different diffusion coefficients, and estimated the corresponding nuclear de-excitation line emission and the ionization rate resulting from the interaction between the penetrating CRs and gases. We find that future MeV observations can be used as a unique probe to measure the low-energy CR density in situ and test different CR propagation scenario inside GMCs.