Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2009-01-08
Astrophys.J.694:257-267,2009
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
13 pages, 4 figures, 3 tables, accepted by ApJ
Scientific paper
10.1088/0004-637X/694/1/257
Diffuse interstellar clouds show large abundances of H_3^+ which can be maintained only by a high ionization rate of H_2. Cosmic rays are the dominant ionization mechanism in this environment, so the large ionization rate implies a high cosmic-ray flux, and a large amount of energy residing in cosmic rays. In this paper we find that the standard propagated cosmic-ray spectrum predicts an ionization rate much lower than that inferred from H_3^+. Low-energy (~10 MeV) cosmic rays are the most efficient at ionizing hydrogen, but cannot be directly detected; consequently, an otherwise unobservable enhancement of the low-energy cosmic-ray flux offers a plausible explanation for the H_3^+ results. Beyond ionization, cosmic rays also interact with the interstellar medium by spalling atomic nuclei and exciting atomic nuclear states. These processes produce the light elements Li, Be, and B, as well as gamma-ray lines. To test the consequences of an enhanced low-energy cosmic-ray flux, we adopt two physically-motivated cosmic-ray spectra which by construction reproduce the ionization rate inferred in diffuse clouds, and investigate the implications of these spectra on dense cloud ionization rates, light element abundances, gamma-ray fluxes, and energetics. One spectrum proposed here provides an explanation for the high ionization rate seen in diffuse clouds while still appearing to be broadly consistent with other observables, but the shape of this spectrum suggests that supernovae remnants may not be the predominant accelerators of low-energy cosmic rays.
Fields Brian D.
Indriolo Nick
McCall Benjamin J.
No associations
LandOfFree
The Implications of a High Cosmic-Ray Ionization Rate in Diffuse Interstellar Clouds does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Implications of a High Cosmic-Ray Ionization Rate in Diffuse Interstellar Clouds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Implications of a High Cosmic-Ray Ionization Rate in Diffuse Interstellar Clouds will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-543991