Rigorous Theory for Secondary Cosmic-Ray Ionization
Abstract
The energy spectrum of electrons produced in molecular gas by interstellar cosmic rays (CRs) is rigorously calculated as a function of gas column density N traversed by the CRs. This allows us to accurately compute the local value of the secondary ionization rate of molecular hydrogen, ${\zeta }_{\sec }(N)$ , as a function of the local primary ionization rate, ζp(N). The ratio ${\zeta }_{\sec }/{\zeta }_{p}$ increases monotonically with N, and can considerably exceed the value of ≈0.67 commonly adopted in the literature. For sufficiently soft interstellar spectra, the dependence ${\zeta }_{\sec }/{\zeta }_{p}$ versus N is practically insensitive to their particular shape and thus is a general characteristic of the secondary CR ionization in dense gas.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2021
- DOI:
- 10.3847/1538-4357/abdc27
- arXiv:
- arXiv:2101.05803
- Bibcode:
- 2021ApJ...909..107I
- Keywords:
-
- Secondary cosmic rays;
- Molecular clouds;
- 1438;
- 1072;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted to ApJ