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, ${\zeta }_p(N)$. The ratio ${\zeta }_{\sec }/{\zeta }_p$ increases monotonically with $N$, and can considerably exceed the value of $\approx 0.67$ 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.

Accepted to ApJ

References in corpus (4)

• The Different Structures of the Two Classes of Starless Cores
• Decoupling of Magnetic Fields in Collapsing Protostellar Envelopes and Disk Formation and Fragmentation
• Chemistry and Radiative Transfer of Water in Cold, Dense Clouds
• Diffusive Versus Free-Streaming Cosmic Ray Transport in Molecular Clouds