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 (15)

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• The cosmic-ray ionisation rate in the pre-stellar core L1544
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• Cosmic Ray Interstellar Propagation Tool using Itô Calculus (criptic): software for simultaneous calculation of cosmic ray transport and observational signatures
• The Effects of Cosmic Rays on the Chemistry of Dense Cores
• Cosmic-ray-induced H${}_2$ line emission: Astrochemical modeling and implications for JWST observations
• Self-discharge by streaming cosmic rays
• The first detection of cosmic-ray excited H${}_2$ in interstellar space
• A low cosmic-ray ionisation rate in the prestellar core Ophiuchus/H-MM1. Mapping of the molecular ions ortho-H2D+, N2H+, and DCO+
• Are Stellar Embryos in Perseus Radio-Synchrotron Emitters? Statistical data analysis with Herschel and LOFAR paving the way for the SKA