The Composition of Cosmic Rays and the Mixing of the Interstellar Medium |
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Authors: | R E Lingenfelter J C Higdon |
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Institution: | (1) Center for Astrophysics and Space Sciences, University of California San Diego, La Jolla, CA 92093, USA;(2) W.M. Keck Science Center, Claremont Colleges, Claremont, CA 91711-5916, USA |
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Abstract: | The differences between the composition of Galactic cosmic rays and that of the interstellar medium are manifold, and they
contain a wealth of information about the varying processes that created them. These differences reveal much about the initial
mixing of freshly synthesized matter, the chemistry and differentiation of the interstellar medium, and the mechanisms and
environment of ion injection and acceleration. Here we briefly explore these processes and show how they combine to create
the peculiar, but potentially universal, composition of the cosmic rays and how measurements of the composition can provide
a unique measure of the mixing ratio of the fresh supernova ejecta and the old interstellar medium in this initial phase of
interstellar mixing.
In particular, we show that the major abundance differences between the cosmic rays and the average interstellar medium can
all result from cosmic ray ion injection by sputtering and scattering from fast refractory oxide grains in a mix of fresh
supernova ejecta and old interstellar material. Since the bulk of the Galactic supernovae occur in the cores of superbubbles,
the bulk of the cosmic rays are accelerated there out of such a mix. We show that the major abundance differences all imply
a mixing ratio of the total masses of fresh supernova ejecta and old interstellar material in such cores is roughly 1 to 4.
That means that the metallicity of ∼3 times solar, since the ejecta has a metallicity of ∼8 times that of the present interstellar
medium. |
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Keywords: | Cosmic rays Dust ISM: abundances ISM: bubbles Stars: Wolf Rayet Supernovae: general |
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