Nuclear de-excitation line emissions from giant molecular clouds

¹ CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, School of Physical Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
² Deep Space Exploration Laboratory, Hefei 230088, China
³ School of Astronomy and Space Science, University of Science and Technology of China, Hefei, Anhui 230026, China
⁴ TIANFU Cosmic Ray Research Center, Chengdu, Sichuan, China

^★ Corresponding author; lbing@ustc.edu.cn

Received: 23 August 2024
Accepted: 6 November 2024

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.