Work

Constraining the low-energy cosmic ray flux in the central molecular zone from MeV nuclear deexcitation line observations

Year: 2024

Type: article

Abstract: Low-energy cosmic rays (LECRs) dominate the ionization in dense regions of molecular clouds in which other ionizers such as UV or x-ray photons are effectively shielded. Thus, it was argued that the high ionization rate at the central molecular zone (CMZ) of our Galaxy is mainly caused by LECRs. However, the required LECR flux is orders of magnitude higher than the extrapolation of GeV cosmic ray (CR) flux derived from GeV $\ensuremath{\gamma}$-ray observations. In this paper, we considered two types of additional LECR components and found that only very soft anomalous CR components can explain such a high ionization rate. This LECR component will inevitably produce MeV nuclear deexcitation lines due to their inelastic scattering with the ambient gas. We calculated the MeV line emission and discussed the detectability of next-generation MeV instruments. We found that future MeV observations can be used to pin down the origin of the high ionization rate in the CMZ.

Source: Physical review. D/Physical review. D.

DOI: 10.1103/physrevd.110.063033

Authors: Bing Liu, Ruizhi Yang

Institutions: University of Science and Technology of China, Deep Space Exploration Laboratory

Language: English

Topic: Astrophysics and Cosmic Phenomena

Subfield: Nuclear and High Energy Physics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: green

Funder: National Natural Science Foundation of China

Awards: G4808638889, G4905711022, G5776882564