Detection of radio recombination lines of hydrogen ionized by cosmic-ray protons in the cool interstellar medium

摘要

The emission of hydrogen radio recombination lines from a cloud of cool interstellar matter toward the radio source Cassiopeia A has been detected. The formation of the radio recombination lines is initiated by cosmic rays. The rate of ionization of the interstellar hydrogen by cosmic-ray protons measured from the radio recombination lines using the most direct method is ζ_H = (1 ± 0.25) × 10~(-16) s~(-1). This value of ζ_H is compared with measurements obtained using other methods.