How to use molecular clouds to study the propagation of cosmic rays in the Galaxy

TL;DR

This paper discusses how gamma-ray observations of molecular clouds can be used to map cosmic ray distribution and diffusion in the Galaxy, providing a new method to study cosmic ray propagation.

Contribution

It introduces a novel approach to constrain cosmic ray diffusion coefficients using gamma-ray data from molecular clouds.

Findings

Gamma-ray emissions reveal cosmic ray spectra in clouds

Method constrains local cosmic ray diffusion coefficients

Supports using molecular clouds as cosmic ray probes

Abstract

Observations of molecular clouds in the gamma ray domain provide us with a tool to study the distribution of cosmic rays in the Galaxy. This is because cosmic rays can penetrate molecular clouds, undergo hadronic interactions in the dense gas, and produce neutral pions that in turn decay into gamma rays. The detection of this radiation allows us to estimate the spectrum and intensity of cosmic rays at the cloud's position. Remarkably, this fact can be used to constrain the cosmic ray diffusion coefficient at specific locations in the Galaxy.